Showing papers in "Ecological Entomology in 2014"

Specialisation of bacterial endosymbionts that protect aphids from parasitoids

Abstract: 1. Infection by the bacterial endosymbiont Hamiltonella defensa is capable of protecting the pea aphid from parasitism by Aphidius ervi and the black bean aphid from parasitism by Lysiphlebus fabarum. Here we investigate protection of a third aphid species, the cowpea aphid, Aphis craccivora, from four parasitoid species: Binodoxys communis, B. koreanus, Lysiphlebus orientalis, and Aphidius colemani. 2. We compared parasitism of A. craccivora lines that were either infected with, or cured of H. defensa separately for the four parasitoid species. Infection by H. defensa almost completely eliminated parasitism of A. craccivora by B. communis and B. koreanus, but had no effect on parasitism by L. orientalis and A. colemani. 3. This indicates at least genus-level specificity of protective effects by H. defensa and we discuss implications of our findings on the known world-wide distribution of this host/symbiont interaction.

Self-medication in insects: current evidence and future perspectives

Abstract: 1. Self-medication is an ability to consume or otherwise contact biologically active organic compounds specifically for the purpose of helping to clear a (parasitic) infection or reduce its symptoms. Consumption of these compounds may either take place before the infection is contracted (prophylactic consumption) or after the infection is contracted (therapeutic consumption). 2. An important insight is that self-medication is a form of adaptive plasticity, and as such, consumption of the medicinal substance when uninfected must impose a fitness cost (otherwise the substance would be universally consumed). This distinguishes self-medication from several closely related phenomena such as microbiome effects or compensatory diet choice. 3. A number of recent studies have convincingly demonstrated self-medication within several different, distantly-related, insect taxa. Here I review evidence of self-medication in the wooly bear caterpillar Grammia incorrupta Edwards, the armyworm Spodoptera Guenee, the fruit fly Drosophila melanogaster Meigen, the monarch butterfly Danaus plexippus Kluk, and the honey bee Apis mellifera Linnaeus. 4. These studies show not only that self-medication is possible, but that the target of the medication behaviour may in some cases be kin rather than self. They also reveal very few general patterns. I therefore end by discussing future prospects within the field of insect self-medication. (Less)

Effects of altered precipitation on insect community composition and structure in a meadow steppe

Abstract: Precipitation can be a key driver of ecosystem functioning in semi-arid and arid grasslands. Altered precipitation patterns had significant impacts on plant community dynamics, which in turn influenced the community composition and structure of higher trophic levels, especially insects, in grasslands. A field experiment was conducted by manipulating the amount of natural precipitation (control, +30% rainfall, and −30% rainfall) to examine the effects of altered precipitation patterns on insect diversity, abundance, and trophic structure in a meadow steppe over 3 years (2007–2009). The results showed that the increased precipitation treatment significantly enhanced above-ground biomass of the entire plant community and particularly grasses, whereas the decreased precipitation treatment significantly reduced them. There were year-to-year changes in species richness, Shannon–Wiener index, and abundance of the whole insect community. Both increased and decreased precipitation caused declines in insect species richness and abundance owing to potentially complex vegetation-mediated effects and direct habitat effects. The abundance of each trophic guild in the insect community responded differently to altered precipitation patterns, with lower herbivore abundance and unchanged abundance of predators and parasitoids. Thus changes in precipitation may generate an insect community that is increasingly dominated by secondary consumers. The present results suggest that altered precipitation causes a declines in insect diversity and shifts in trophic structure, potentially influencing ecosystem functioning in grasslands. Additionally, the inter-annual variation in the insect community under altered precipitation highlights the importance of long-term experiments for drawing correct conclusions about the impacts of climate change on grassland ecosystems.

Floral resources, body size, and surrounding landscape influence bee community assemblages in oak‐savannah fragments

Abstract: Fragmentation of natural habitats due to urban development is predicted to have negative impacts on species diversity. The surrounding landscape (or ‘matrix’) of urban or semi-natural habitats can sometimes support biodiversity, but the amount of support will depend on species-specific traits, and on the resources available in the fragment and the matrix. Using data on bees collected from 19 oak-savannah fragments, the question of whether bee communities differ when fragments are embedded in different landscapes (Douglas-fir forest vs. urban residential neighbourhoods) was investigated, and also whether these differences could be attributed to species-specific traits of bees (e.g. body size, specialization) and/or within-fragment floral resources. No differences were found in overall richness or abundance of bees, but there were distinct differences in plant and bee community composition between matrix types. Common wood-nesters and late-flying, small-bodied bees tended to be found in urban-associated fragments, which also had a lower availability of within-fragment floral resources. Forest-associated fragments, on the other hand, had a greater density and richness of early-flowering native plant species, and supported a higher abundance of large-bodied bee species. Bumble bee abundance, in particular, increased with increasing proportion of forest cover in the surrounding landscape. Large-bodied bees appear to respond to increased availability of within-fragment floral resources, but it was also hypothesised that nesting and floral resources in matrix habitat drive the differences in bee community assemblages.

Priority effects on the life-history traits of two carrion blow fly (Diptera, Calliphoridae) species

Abstract: Third instars of the invasive blow fly Chrysomya rufifacies are facultative predators on larvae of the native blow fly Cochliomyia macellaria. 2. The effects of priority arrival time on the survivorship and fitness of C. rufifacies andC. macellaria were investigated in laboratory experiments. 3. Cochliomyia macellaria colonising a resource within 1-2 days after C. rufifacies resulted in a 20-70% reduction in survivorship, pupal weight and fecundity compared with those colonising a resource more than 2 days before or after C. rufifacies .I nv erly , C. rufifacies exhibited a 50% increase in survivorship and fecundity when closely (∼2 days) associated temporally on the resource with C. macellaria and was negatively affected by disparate arrival. 4. These results demonstrate that arrival sequence significantly affects the fitness of both C. rufifacies andC. macellaria. Early colonisation may allow C. macellaria to persist in a community, while there are fitness benefits for C. rufifacies colonising after C. macellaria. 5. The 60% reduction in C. macellaria survivorship when in close temporal association with C. rufifacies may act as an agent of selection for C. macellaria to colonise a resource early and develop quickly to avoid predation on resources colonised by C. rufifacies . 6. Selection for such traits may explain how C. macellaria is able to persist despite intraguild predation by this invasive species. In contrast, the 50% increase in survivorship and fecundity exhibited by C. rufifacies when arriving after C. macellaria may select for C. rufifacies to delay colonisation.

Parasitoid genus-specific manipulation of orb-web host spiders (Araneae, Araneidae)

Abstract: Araneid spiders of genus Araniella are attacked by three polysphinctine parsitoid wasps Polysphincta boopsTschek, P. tuberose (Gravenhorst), and Sinarachna pallipes (Holmgren). In the present study, the trophic niche of sympatrically occurring parasitoids and the host manipulation they induced were studied. The aim was to identify whether the variation in host response to manipulation is as a result of differences among parasitoids or among host species. It was found that final instar larva forced the spider host to build a three-dimensional (3D) ‘cocoon web’ to protect the parasitoid during pupation. The behaviour of parasitoid larva and the induced modification of the web architecture differed between wasps of genus Polysphincta and Sinarachna but not among three spider species. The larvae of genus Polysphincta forced the spider host to build the ‘cocoon web’ with a high thread density within which the pupa was positioned horizontally. The larvae of Sinarachna forced the spider host to build web with sparse threads and the pupa was positioned vertically in the middle of the ‘cocoon web’. There seems to be an investment trade-off in parasitoid wasps: some species manipulate the host to build a dense protective web, while pupating in a sparse cocoon, whereas others make the spider produce a sparse web but build a dense pupa wall.

The volatile organic compounds of introduced and native dung and carrion and their role in dung beetle foraging behaviour

Abstract: 1. The decomposition of biological material produces a plethora of volatile organic compounds (VOCs), which are implicated in the foraging behaviour of coprophagous and necrophagous insects. Dung beetles (Coleoptera: Scarabaeidae: Scarabaeinae) have an acute olfactory system used to locate food resources. Accordingly, identification of food resource VOCs potentially used in food location is integral to understanding dung beetle foraging ecology. 2. In this study, volatile emissions from dung and carrion of native and introduced animals in New Zealand were analysed using solid-phase microextraction (SPME) and gas chromatography-mass spectrometry (GC-MS). Volatile profiles were compared via principal component analyses (PCAs) and cluster solutions based on attractiveness using canonical discriminant analysis (CDA). 3. A total of 115 compounds were detected from 21 food types. Statistical analyses showed that dung and carrion volatile profiles clustered according to attractiveness to the dung beetle Saphobius edwardsi, and that different dung types formed distinct clusters and grouped separately from carrion. 4. This study suggests that volatile profiles emitted by food resources used by dung beetles are complex, producing distinct odours, which potentially mediate foraging decisions.

Natural enemies of natural enemies: the potential top‐down impact of predators on entomopathogenic nematode populations

Abstract: Top-down population regulation can influence the success of biological control agents when they are released into the field. Entomopathogenic nematodes (EPNs) are used commonly in biological control programmes, but their efficacy suffers from poor persistence. Although abiotic soil conditions have been shown to reduce EPN persistence, consumption of infected insects by scavengers and of infective juvenile (IJ) nematodes by predators may also regulate these populations. In the present study, the effects of different soil arthropods on EPNs in laboratory conditions were measured. It was hypothesised that arthropods commonly found in soil communities where EPNs are applied would consume cadavers of insects parasitised by the nematodes and the IJs themselves. Some species of scavengers consume EPN-infected insects. Crickets (Gryllus bimaculatus De Geer), American cockroaches [Periplaneta Americana (Linnaeus)], ants [Tetramorium chefketi Forel and Pheidole pallidula (Nylander)], earwigs (Labidura riparia Pallas), mites (Sancassania polyphyllae Zachvatkin), and springtails (Sinella curviseta Brook and Folsomia candida Willem) have different responses to nematode-killed insects. Results suggested that ants (T. chefketi), cockroaches, mites, and earwigs fed on Steinernema-killed insects whereas neither crickets nor springtails consumed them. In the second part of the study, experiments were conducted to determine whether mites and springtails consumed IJ EPNs. Results showed that S. polyphyllae mites do not consume infective juveniles in soil, whereas both springtail species consumed significant numbers of the IJs. Top-down regulatory processes can be a limiting factor for EPN populations under laboratory conditions. Both host cadavers and IJs are consumed (albeit by different arthropods), so these results may help explain the difficulties associated with the persistence of EPN application to soil.

Effects of predation risk and plant resistance on Manduca sexta caterpillar feeding behaviour and physiology

Abstract: Because predation risk typically alters how prey forage for food, interactions between predation risk and food availability are commonly found. Less is known about how host plant quality and predation risk interact to affect prey behaviour and physiology. Using the caterpillar, Manduca sexta, and its predator, Podisus maculiventris, the effects of predation risk and host plant quality on caterpillar feeding, growth, assimilation efficiency, and resting metabolic rate were tested. Overall, caterpillars on low-resistance tomato plants (jasmonate-insensitive) gained 14% more mass than caterpillars on high-resistance plants (wild-type tomato). On low-resistance plants, the presence of predators caused caterpillars to eat 32% less, but they gained the same mass as unthreatened caterpillars (i.e. a 19% increase in assimilation efficiency). In addition, caterpillars showed a 17% increase in resting metabolic rate in the presence of predators. On high-resistance plants, predation risk caused a decrease in feeding, but did not alter assimilation efficiency or resting metabolic rate. The reduction in physiological responses to predation risk on high- versus low-resistance plants demonstrates a tradeoff between the ability to respond to predation risk and the ability to grow, especially on well-defended plants.

Patterns of parasite infection in bumble bees (Bombus spp.) of Northern Virginia

Abstract: In recent decades, several North American bumble bee (Bombus spp.) species have undergone precipitous declines. It is suspected that a parasite or pathogen may be responsible, yet few studies have examined the extent of parasitism and the ecology of host–parasite relationships in U.S. bumble bee populations. A season-long survey of bumble bees in seven grassland meadows of the northern Shenandoah Valley and Piedmont regions in Virginia was conducted in 2011 to ascertain the local prevalence and predictors of parasitism by the internal parasites Nosema and Crithidia, and by parasitoid conopid flies. In total, 835 bumble bees representing six species were examined. Using visual detection methods, we determined that 25% of bees were infected with parasitoid larvae, 17.4% with Crithidia, and 7.3% with Nosema. Nosema infections were more prevalent and intense in locally rare than locally common species, with the two rarest bumble bees [B. fervidus (Fabricius) and B. auricomus (Robertson)], newly suspected to be in decline, having the highest frequencies of infection (11–17.8%). Crithidia was generally more prevalent in common bumble bee species (11–35%). With fewer than 5% of individuals infected, the two rarest species had the lowest frequencies of Crithidia. Conopid fly larvae were more prevalent in common species. Body size significantly influenced the probability of parasitism by conopids and Crithidia. Smaller bees were more likely to be parasitised by Crithidia. Larger bees were more likely to be parasitised by conopid flies, although the largest bee species (B. auricomus) was not infected by conopids in this study.

Body size and elevation: do Bergmann's and Rensch's rule apply in the polytypic bushcricket Poecilimon veluchianus?

Abstract: 1. One of the most fundamental differences between animals are size differences that are often prominent when comparing species, as well as the sexes within species. One important aim of evolutionary and ecological studies is therefore to understand the pattern of size variation. 2. Bergmann’s rule and Rensch’s rule are two ideas that describe such general patterns. But whether or not these rules apply only in homoeothermic animals, or also in insects, is unclear because previous studies have shown opposing results. 3. For two subspecies of Poecilimon veluchianus Ramme (Orthoptera: Tettigoni- idae), we demonstrate a pattern that is opposite to what is predicted by Bergmann’s rule. Rensch’s rule also does not seem to apply, as sexual size dimorphism (SSD) does not change even though body size decreases with elevation in these two taxa. Our data adds to an emerging pattern that the two rules are not universally applicable in insects.

Tree diversity promotes predator but not omnivore ants in a subtropical Chinese forest

Abstract: 1. Epigeic ants are functionally important arthropods in tropical and subtropical forests, particularly by acting as predators. High predation pressure has been hypothesised to be a mechanism facilitating high diversity across trophic levels. 2. In this study, standardised pitfall traps were used in a highly diverse subtropical forest to test if and how ant species richness is related to tree species richness and a comprehensive set of other environmental variables such as successional age, soil properties or elevation. 3. A total of 13 441 ant individuals belonging to 3839 species occurrences and 71 species were collected, of which 26 species were exclusive predators and 45 species were omnivores. 4. Occurrence and species richness of total and omnivore ants were positively related to soil pH. Predator ant occurrence was unrelated to all environmental variables tested. 5. The species richness of predator ants increased with tree species richness but decreased with leaf functional diversity and shrub cover. Elevation negatively influenced only total ant species richness. 6. The evenness of predators increased with tree species richness, while the evenness of all ants decreased with shrub cover. Omnivore ant evenness decreased with tree evenness, but increased with successional age. 7. The results highlight the value of diverse forests in maintaining species richness and community evenness of a functionally important predator group. Moreover, the results stress the importance of analysing trophic groups separately when investigating biodiversity effects.

Thermal change alters the outcome of behavioural interactions between antagonistic partners

Abstract: 1. Concerns about climate change often trigger the question whether physiological and behavioural responses of species will enable them to persist. However, species do not exist alone and are largely dependent on interactions with others within communities. 2. In the present study, a mechanistic approach is used to test the hypothesis that inter-specific differences in metabolic response to unpredictable short-term thermal changes can change the outcome of host–parasitoid behavioural interactions. 3. The effect of a drop or a rise of 5 °C on resting metabolic rates (RMR) of the main aphid pest of cereal crops in Western Europe, the host Sitobion avenae Fabricius and its main natural enemy, the parasitoid Aphidius rhopalosiphi De Stefani-Perez was measured. Also, defence and attack behaviours were measured for host and parasitoid separately as well as in interaction, since behavioural strategies of both species largely determine parasitism success. 4. The results showed that, when no change in temperature occurred, parasitoids had the highest oviposition rate. However, only with a rise of temperature behavioural interactions were disrupted: the parasitoid attack rate decreased whereas the aphid defence rate increased. This alteration in behaviour was associated with a stronger thermal response of RMR in hosts than in parasitoids, suggesting that species-specific thermal responses of RMR could give valuable information on changes in the outcome of species interactions under warm spells but not under cold ones. 5. It was shown that relatively modest thermal changes with non-lethal effects can have profound consequences for interacting co-evolved species which may affect ecosystem services, such as biological control of pest populations.

Food plant and herbivore host species affect the outcome of intrinsic competition among parasitoid larvae

Abstract: 1. In nature, several parasitoid species often exploit the same stages of a common herbivore host species and are able to coexist despite competitive interactions amongst them. Less is known about the direct effects of resource quality on intrinsic interactions between immature parasitoid stages. The present study is based on the hypothesis that variation in the quality or type of plant resources on which the parasitoids indirectly develop may be complementary and thus facilitate niche segregation favouring different parasitoids in intrinsic competition under different dietary regimes. 2. The present study investigated whether two herbivore species, the cabbage butterflies Pieris brassicae and Pieris rapae (Pieridae), and the quality of two important food plants, Brassica oleracea and Brassica nigra (Brassicaceae), affect the outcome of intrinsic competition between their primary larval endoparasitoids, the gregarious Cotesia glomerata (Braconidae) and the solitary Hyposoter ebeninus (Ichneumonidae). 3. Hyposoter ebeninus is generally an intrinsically superior competitor over C.glomerata. However, C.glomerata survived more antagonistic encounters with H.ebeninus when both developed in P.brassicae rather than in P.rapae caterpillars, and while its host was feeding on B.nigra rather than B.oleracea. Moreover, H.ebeninus benefitted from competition by its higher survival in multiparasitised hosts. 4. These results show that both plant and herbivore species mediate the battleground on which competitive interactions between parasitoids are played out and may affect the outcomes of these interactions in ways that enable parasitoids to segregate their niches. This in turn may promote coexistence among parasitoid species that are associated with the same herbivore host.

Parental care influences social immunity in burying beetle larvae

Abstract: 1. We provide evidence for social immunity in offspring of a sub-social species, the burying beetle, Nicrophorus vespilloides. 2. N. vespilloides is a carrion breeder, and in a similar fashion to the adult beetles, the offspring produce exudates that exhibit lytic activity, which are used to coat the breeding resource. This strategy defends against the microbial community. 3. The lytic activity in larval exudates declines as the brood develops, perhaps being most beneficial at the start of the breeding bout. 4. Changing levels of parental care through widowing/orphaning affects lytic activity in the larval exudates, with levels decreasing in the absence of both parents.

Seed handling behaviours of native and invasive seed-dispersing ants differentially influence seedling emergence in an introduced plant

Abstract: Myrmecochory, or ant-mediated seed dispersal, is an important ecological interaction in which ants benefit by gaining nutrition from lipid-rich elaiosomes attached to seeds and plants benefit from having their seeds dispersed away from parent plants. Most research on the benefits of myrmecochory focuses on primary dispersal, in which ants move seeds to nests, or secondary dispersal, in which ants deposit intact seeds in middens after consuming elaiosomes. Less is known about how ants handle seeds inside nests and if handling influences plant fitness. The seed handling behaviours of a native ‘keystone disperser’, Aphaenogaster rudis s.l., and an invasive seed-disperser, Myrmica rubra L., on an introduced herb, Chelidonium majus L., were compared. We conducted a greenhouse experiment to test if handling by ants, manual removal of elaiosomes, or no handling (controls) influenced seedling emergence. Colony-level differences in handling behaviours and plant responses were also examined. Aphaenogaster rudis retained seeds inside nests longer than M. rubra, but there was no difference in the amount of elaiosome removed by the two species. There was no difference in the proportion of seedlings that emerged among treatments, but seedlings emerged earlier when handled by A. rudis. Additionally, more seedlings emerged and seedlings emerged earlier the longer seeds were retained inside ant nests. This study suggests that handling by ants may be a benefit of myrmecochory. This is probably not due to elaiosome removal; rather favourable nest conditions may enhance emergence. Also, functional differences in ant species may result in different outcomes for plant partners.

The developmental strategies and related profitability of an idiobiont ectoparasitoid Sclerodermus pupariae vary with host size

Abstract: Parasitoids can encounter patches of hosts of varying sizes. Trade-offs may result in different developmental strategies and fitness characteristics in parasitoids. To explore developmental strategies and host suitability of a bethylid parasitoid, Sclerodermus pupariae, in relation to the size of oak long-horned beetle larvae, Massicus raddei, effects of host size on parasitoid fitness parameters were tested under laboratory conditions. Maternal parasitoids obtained lower rates of parasitism when inoculating small or large hosts due to early host death and parasitoid injury, respectively, indicating significant fitness costs associated with paralysing those host sizes. Host size was shown to have highly variable effects on selected fitness parameters. For maternal females, increasing initial host size led to increasing host handling time, and fertility exhibited a parabolic relationship with host size. The highest fertility was exhibited when parasitoids oviposited on medium-sized hosts. Host size effects were very apparent for parasitoid offspring, with the largest hosts producing later-emerging but larger females. Parasitoid offspring sex ratios in all host size classes were significantly female-biased, and exhibited a quadratic function with increasing host size. Assessment of host profitability revealed that medium-sized hosts presented the best fitness return for the parasitoids. The findings suggest that this bethylid parasitoid can achieve a compromise in optimisation of the two most important fitness functions when encountering an abundance of different-sized hosts.

Photoperiod and variation in life history traits in core and peripheral populations in the damselfly Lestes sponsa

Abstract: In order to predict evolutionary responses to environmental changes one needs to identify the evolutionary potential in terms of genetic variation of traits and of the traits' plasticity. We studie ...

Time of the season: the effect of host photoperiodism on diapause induction in an insect herbivore, Leptinotarsa decemlineata

Abstract: Diapause, seasonal physiological dormancy, is the primary life history strategy used by insect species inhabiting temperate climates for seasonal synchronisation. Biotic signals for diapause induction originating from host plants may provide dependable cues for insects expanding from subtropical regions. We investigated the effect of plant-mediated photoperiod cues on diapause initiation within the Colorado potato beetle, Leptinotarsa decemlineata Say. The effect of photoperiod changes on potato leaf composition and its subsequent correlation with diapause initiation was tested. Analyses revealed a significant effect of short-day (LD 8 : 16 h and LD 10 : 14 h) photoperiod growth regimens on both nitrogen content in potato leaves and diapause initiation within L. decemlineata. Potato plants grown under short day conditions displayed significantly higher levels of leaf nitrogen compared with long-day treated plants. Over 65% of beetles feeding upon short-day treated plants initiated diapause compared with < 20% of beetles placed upon long-day treated plants. The observation of seasonality-induced diapause signals by host plants signifies an important addition to the current array of plant–insect interactions. The present results suggest that seasonal synchrony may be the result of a more integrated system whereby host plant photoperiodism acts as an intermediate or supplementary physiological cue for diapause initiation.

Terrestrial deposition of aquatic insects increases plant quality for insect herbivores and herbivore density

Abstract: 1. Mobile organisms such as emergent aquatic insects can subsidise land with aquatic nutrients, creating a link between terrestrial and aquatic ecosystems. 2. Deposition of aquatic insects on land produces bottom-up effects in arthropod detritivore communities and may also affect plants and plant–herbivore interactions. 3. To investigate the effects of insect deposition on plant–herbivore interactions, we conducted a field experiment and surveys of tealeaf willow (Salicaceae; Salix phylicifolia Coste) and July highflyer caterpillars (Geometridae; Hydriomena furcata Thunberg) at lakes in Northeast Iceland with either high- or low-midge density and deposition to land. 4. It was found that willow at high-midge lakes had 8–11% higher nitrogen content compared with willow at low-midge lakes. In addition, natural caterpillar density was 4–6 times higher and caterpillars were 72% heavier at high-midge lakes than low-midge lakes. 5. A fully reciprocal caterpillar transplant experiment among willow at high- and low-midge lakes was performed to separate the influence of habitat and midge effects on caterpillar performance. 6. After transplant, pupae of July Highflyer caterpillars were on average 11% heavier at high-midge sites compared with low-midge sites. However, this difference was not statistically significant. 7. The present findings indicate that cross-ecosystem subsidies in the form of aquatic insects can increase plant foliar quality and the abundance of insect herbivores in recipient ecosystems.

Intra‐population genetic variation in diapause incidence of adult‐diapausing Tetranychus pueraricola (Acari: Tetranychidae)

Abstract: Diapause is an important seasonal adaptation for arthropods in temperate regions. Recent global warming has had a profound effect on the timing of diapause induction, but the potential for evolutionary changes in diapause attributes remains largely unknown because of a scarcity of information about genetic architecture in these traits. Genetic variation in diapause incidence within a population and the genetic correlation with different environmental conditions are both important for predicting evolutionary responses to climatic changes. The main aim of this study was to determine these parameters at temperatures representative of the winter season (stationary 18–20 °C) by using 12 isofemale lines established from females of a single population of the adult-diapausing spider mite Tetranychus pueraricola (Acari: Tetranychidae). To compare the response between field and laboratory, their ancestral phenotypes were randomly chosen from diapausing (eight) or non-diapausing (four) females. Diapause incidence was investigated at 18, 19, and 20 °C under LD 10:14 h conditions with two to five replicates for each strain. At 18 °C, more than 90% of the females entered diapause, and the genetic variation among strains (intraclass correlation coefficient; ICC) was relatively small (44%), whereas highly variable diapause incidences were observed for the warmer conditions (both 87% ICC). The correlation between temperatures was as high as 0.79 between 19 and 20 °C, whereas the correlation estimates between 18 and either 19 or 20 °C were still positive, but not significant. In addition, the analyses demonstrated the existence of variation in the entire response curves (significant genotype × environment interaction). These results demonstrate that significant genetic variation in response curves is maintained in this population, and accordingly this population has a capacity to respond to climatic changes. Crossing reaction curves across temperatures may prevent the fixation of a single optimal response curve, and maintain genetic variation at each temperature.

Emergent effects of ground beetles size diversity on the strength of prey suppression

Abstract: Determining how multiple predators provide better prey suppression is a key step towards developing conservation biological control strategies. While numerous previous studies have demonstrated that diverse predator assemblages can be more effective in controlling pest populations, others have shown that it is the presence or absence of competitively superior species that is critical to pest biological control (i.e. selection effect). The present study investigated how increasing ground beetle body size diversity increases prey suppression. A mesocosm experiment was conducted to compare invertebrate prey suppression between nine created ground beetle assemblages. Size diversity of these assemblages was manipulated according to three diversity levels: low, medium, and high diversity. Partitioning of the diversity effects revealed that increasing the ground beetle size diversity had no effect on the strength of prey suppression. The absence of an effect of ground beetle size diversity may be because of the absence of resource partitioning among different-sized ground beetles. The amount and range of prey consumed increased with increasing ground beetle body size. Thus, prey suppression was strongly strengthened by the presence of large ground beetles in the assemblages. The present results suggest that for biological pest control, Agri-managers should emphasise practices that promote the presence of large carabids. This is not only because promoting the presence of large carabids could be at least as effective as conserving a diverse ground beetle community, but also because large ground beetles are more vulnerable to environmental disturbances and to predation than ground beetles of the other size classes.

Survivability and post‐diapause fitness in a scolytid beetle as a function of overwintering developmental stage and the implications for population dynamics

Abstract: 1. It has recently been suggested that expected increases in temperature might lead to an additional generation per season in bark beetles. Thus, populations would grow more rapidly. However, an additional but not fully developed generation could lead to high winter mortality in the pre-imaginal stages. 2. Winter survivability and post-diapause fitness as a function of the overwintering developmental stage of the spruce bark beetle Ips typographus L. were studied along an altitudinal cline. Fitness was tested in terms of weight, lipid content and flight capacity. 3. Mortality was significantly lower and emergence per brood system significantly higher for fully developed adults that entered overwintering than for larvae, pupae or callow adults. 4. Post-diapause fitness in terms of dry weight and flight capacity was significantly higher in individuals that completed development before winter, and lipid contents also showed a trend for being higher in those individuals. 5. In conclusion, in a scenario where effective temperature sums are not adequate for the complete development of an additional generation, models may overestimate population growth by neglecting increased mortality and reduced post-diapause fitness. The results highlight the importance of considering life-history traits and indirect effects in addition to abiotic factors such as temperature when modelling population dynamics.

The seasonal dynamic of ant‐flower networks in a semi‐arid tropical environment

Abstract: Several studies have recently focused on the structure of ecological networks involving ants and plants with extrafloral nectaries; however, little is known about the effects of temporal variation in resource abundance on the structure of ant-plant networks mediated by floral nectar. 2. In this study, it was evaluated how strong seasonality in resource availability in a semi-arid tropical environment affects the structure of ant-flower networks. We recorded ants collecting floral nectar during two seasons (from December 2009 to January 2013): dry and green seasons. Then, we built interaction networks for flower-visiting ants in the Brazilian Caatinga separately for each combination of transect and season. 3. In general, strong seasonality directly influenced patterns of ant-flower interactions and the overall complexity of these ecological networks. During the dry season, networks were more connected, less modular, and exhibited greater niche overlap of flower-visiting ants than during the green season. Moreover, resource utilisation by ants during the dry season tended to be more aggregated. These findings indicate that during the dry season, ant species tended to share many resource bases, probably owing to lower overall resource availability during this season. Species composition of the ant network component was highly season specific; however, a central core of highly generalised ants was present during both seasons. 4. The stability of this central core between seasons could strongly affect the ecological and evolutionary dynamics of these interaction networks. This study contributes to the understanding of the structure and dynamics of ant-flower interactions in extremely seasonal environments.

Size and sex of cricket prey predict capture by a sphecid wasp

Abstract: Female-biased predation is rare in nature; however, sphecid wasps often take more female than male prey, including Isodontia mexicana, which hunt Oecanthus tree crickets. This study tests the hypothesis that wasps prefer females because they are larger than males. This predicts a female sex bias only for sexually size-dimorphic prey. Prey from artificial I. mexicana nest holes in Central Ontario were compared with surviving crickets sampled from the hunted population. Sex ratios of prey and survivors were examined and compared with the occurrence of female-biased sexual size dimorphism. Logistic regression was used to determine whether body size, sex, species, and life stage of crickets predicted capture by wasps. As predicted, wasps took a disproportionate number of adult females only of sexually size-dimorphic prey Oecanthus nigricornis. No sex bias was found in adult prey of Oecanthus quadripunctatus or in nymphal prey of either species. However, female-biased sexual size dimorphism did not necessitate female-biased predation: even though female O. nigricornis nymphs were larger than males, female nymphs were not hunted more often. Body size was a significant predictor of predation, but this relationship was non-linear. There was also evidence of an interaction among sex, life stage, and body size of prey in relation to predation risk. These results support the size-preference hypothesis, but do not rule out alternative hypotheses. For example, sex differences in behaviour or life-history traits that develop in adulthood may also contribute to differences in predation risk. Predation that consistently targets large adult females of a population may result in evolutionary changes in the behaviour or life history of the prey species.

Optimal progeny body size in a solitary bee, Osmia bicornis (Apoidea: Megachilidae)

Abstract: 1. Females of solitary, nest‐constructing bees determine both sex (haplo‐diploidy) as well as body size (by amount of provision) of each single offspring.

Bumble bee workers drift to conspecific nests at field scales

Abstract: 1. Workers in several bee species travel to conspecific nests (‘drifting’), enter them, and produce male offspring inside them, so acting as intra-specific social parasites. This adds a new dimension to bees' reproductive behaviour and spatial ecology, but the extent to which drifting occurs over field scales, i.e. at natural nest densities in field conditions, has been unclear. 2. Using the bumble bee Bombus terrestris (Linnaeus) as a model system, we sought to determine rates of worker drifting at field scales and the frequency of potential drifter workers in wild nests. 3. A field experiment with 27 colonies showed that workers travelled to, and became accepted in, conspecific nests that were up to 60 m away, although the number of accepted drifter workers within nests fell significantly with distance. The rate at which nests were entered by drifters was relatively high and significantly exceeded the rate at which drifters became accepted. 4. Microsatellite genotyping of eight field-collected nests from Greater London, U.K., showed that a low frequency (3%) of workers were not full sisters of nestmate workers and hence were likely to have been drifter workers. 5. It is therefore concluded that workers can drift to conspecific nests over field scales and confirmed that successful drifting occurs in natural populations. Drifting appears to be a natural but low-frequency behaviour permitting B. terrestris workers to gain direct fitness.

Oviposition habitat selection by container-dwelling mosquitoes: responses to cues of larval and detritus abundances in the field.

Abstract: Insects’ oviposition responses to resource and larval densities can be important factors determining distributions and competitive interactions of larvae. Aedes albopictus (Skuse) and Aedes aegypti (L.) (Diptera: Culicidae) show aggregated distributions of larvae in the field, larval interactions that are affected by detritus resources, and oviposition responses to resource and density cues in the laboratory. We conducted field experiments testing whether these species choose oviposition sites in response to chemical cues indicating detritus resource quantity and quality or larval abundances. In experiment 1, both species showed interactive responses to water conditioned with high or low quantities of senescent live oak leaves and density combinations of A. albopictus and A. aegypti larvae. Aedes aegypti preferred high-detritus containers when conspecifics were absent. Aedes albopictus tended to prefer high-detritus containers when larval density was low. We found no evidence of interspecific differences in oviposition preferences. In experiment 2, A. albopictus preferred high detritus over low or no detritus, and rapidly-decaying, high-quality detritus over low-quality detritus. Oviposition choices by these Aedes are mainly determined by resource quantity and quality, with larval densities having minor, variable effects. Oviposition responses of these species are unlikely to lead to resource partitioning. Aggregated distributions of these species in the field are unlikely to be products of oviposition choices based on larval densities. Keywords: oviposition choice, resource abundance, larval density, Aedes aegypti, Aedes albopictus, aggregation, resource partitioning Introduction Habitat selection theory predicts that organisms will disperse and colonize habitats in a way that maximizes expected fitness (Resetarits 1996, Binckley & Resetarits 2005, 2008, Resetarits & Binckley 2009). For species that provide no parental care to offspring deposited in discrete patches, selection on the ability to discriminate favorable and unfavorable patches should be particularly strong because offspring are confined to a patch until some developmental milestone is reached (Resetarits & Wilbur 1989). In many patchy-systems such as Drosophila-colonized fruits and mushrooms (e.g., Atkinson 1985) and aquatic container communities (e.g., Juliano 1998), resource competition within a patch is important and may be a significant source of larval mortality, hence female oviposition decisions should minimize the future experience of competition by her larvae. Container-dwelling mosquitoes seem particularly capable of responding to volatile chemical cues that may reflect current or future intensity of larval competition. For example, the presence of con- and heterospecific competitors (Zahiri et al. 1997, Edgerly et al. 1999) or the quantity and type of resources present in a container (Ponnusamy et al. 2008, Reiskind et al. 2009) can influence oviposition choices in these systems. Aedes aegypti and Aedes albopictus are container-dwelling mosquitoes that inhabit human-dominated landscapes throughout the world. Both are competent vectors of multiple arboviruses and thus their reproductive and oviposition behaviours have received much attention (e.g., Sucharit et al. 1980, Allan & Kline 1998, Sharma et al. 2008). Aedes aegypti responds to cues from eggs and larvae of both conspecifics and heterospecifics, including A. albopictus (Zahiri et al. 1997, Allan & Kline 1998). Behavioural assays often test the response of gravid females to water conditioned by larvae or eggs although specific chemical cues have also been isolated and assayed in oviposition trials (Zahiri et al. 1997, Ganesan et al. 2006, Seenivasagan et al. 2009). Aedes aegypti females respond positively to chemical cues derived from well-fed and healthy larvae, but may be repelled by chemical cues from larvae at very high densities or from starved larvae (Zahiri et al. 1997, Allan & Kline 1998, Zahiri & Rau 1998, Seenivasagan et al. 2009). Cues indicating resource availability in a container also elicit oviposition responses from these species. Chemical cues associated with microorganisms from decaying organic matter elicit positive oviposition responses from both A. albopictus (Trexler et al. 2003) and A. aegypti (Benzon & Apperson 1988, Ponnusamy et al. 2008). Reiskind et al. (2009) reported oviposition preference of A. albopictus for containers with oak leaves over containers with grape leaves or plain water. In larval competition experiments oak leaves are a superior resource compared to grape leaves, suggesting that A. albopictus selects oviposition sites that will reduce larval competition and maximize expected fitness (Reiskind et al. 2009). These observations suggest that ovipositing container-dwelling Aedes accurately respond to container conditions, including larval density and resources, as predicted by habitat selection theory. However, most studies have tested oviposition behaviour in the laboratory, under carefully controlled conditions. For example, oviposition assays have been conducted on multi-well plates with water volumes of only a few ml, and water treatments separated by several centimeters or less (Zahiri et al. 1997). Others have used electroantennogram techniques and Y-maze olfactometers to assess the mechanisms eliciting attraction to cues (i.e., behavioural orientation vs. stimulation to oviposit; Seenivasagan et al. 2009). These are effective methods for understanding the proximate causes of these behaviours and the range and strength of responses that can be expected in these species. These studies, as well as a select few field studies (e.g., Trexler et al. 1998), have been largely motivated by the goal of developing attractants or repellents for mosquito control and monitoring, important goals given the human health importance of these species. However, relatively little is known about the importance of such chemical cues in the presence of natural variability, and how they might influence distributions of mosquito eggs across oviposition sites and resulting ecological interactions among larvae. The strong and species-specific responses observed in laboratory experiments may be important drivers of species distributions in wild populations, particularly as they affect densities of individuals relative to local resource availability, and spatial variation of competitive interactions. Understanding responses to these cues in the field and their potential for affecting actual distributions of species, is the goal of this paper. Aedes albopictus and A. aegypti coexist in some areas of the southern United States (O’Meara et al. 1995) despite competitive asymmetry usually favoring A. albopictus (Juliano 1998, 2009, 2010). A leading hypothesis to account for this pattern is condition-specific competition which suggests that the outcome of competition depends on the conditions within larval containers (Juliano 2009, 2010). For example the abundance of rapidly decaying detritus releases A. aegypti from interspecific resource competition with A. albopictus (Daugherty et al. 2000, Murrell & Juliano 2008, Juliano 2010, O’Neal & Juliano 2013). Based on the oviposition experiments discussed above, one hypothesis for coexistence of these species postulates that A. aegypti females select container habitats with higher levels of high-quality resources, stabilizing coexistence via resource partitioning (Shorrocks & Sevenster 1995, Adler et al. 2007). This hypothesis predicts that the two species will show different oviposition responses to detritus resource quantity and quality in the field, and negative correlations of egg numbers. Another coexistence hypothesis in this system is the ‘aggregation model’ of coexistence (Atkinson 1985, Ives 1991) that postulates that intraspecifically aggregated or clumped distributions of larvae among containers will increase intraspecific competition relative to interspecific competition, facilitating coexistence (Ives 1991, Shorrocks & Sevenster 1995, Fader & Juliano 2013). This hypothesis predicts that one or both species preferentially oviposit in containers containing conspecifics in the field. Both A. aegypti and A. albopictus preferentially oviposit in laboratory containers with conspecific larvae or eggs (Allan & Kline 1998) and if this behaviour is prevalent in nature this would directly increase intraspecific aggregation in the field and the likelihood of coexistence (Ives 1991). Aggregated spatial distributions of these species have been observed in the field suggesting aggregation may affect interspecific competition and coexistence (Leisnham & Juliano 2009, Fader & Juliano 2013). These predictions center on oviposition behaviour in response to ecologically realistic cues from detritus or conspecifics at relevant spatial scales in the field. In this paper we describe two experiments testing these hypotheses about oviposition responses of naturally-occurring A. albopictus and A. aegypti females to larval abundance and detritus resource quantity and quality cues at levels likely to be encountered in nature.

Elevated volatile concentrations in high-nutrient plants: do insect herbivores pay a high price for good food?

Abstract: 1. A tritrophic perspective is fundamental for understanding the drivers of insect–plant interactions. While host plant traits can directly affect insect herbivore performance by either inhibiting or altering the nutritional benefits of consumption, they can also have an indirect effect on herbivores by influencing rates of predation or parasitism. 2. Enhancing soil nutrients available to trees of the genus Eucalyptus consistently modifies plant traits, typically improving the nutritional quality of the foliage for insect herbivores. We hypothesised that resulting increases in volatile essential oils could have an indirect negative effect on eucalypt-feeding herbivores by providing their natural enemies with stronger host/prey location cues. 3. Eucalyptus tereticornis Smith seedlings were grown under low- and high-nutrient conditions and the consequences for the release of volatile cues from damaged plants were examined. The influence of 1,8-cineole (the major volatile terpene in many Eucalyptus species) on rates of predation on model caterpillars in the field was then examined. 4. It was found that the emission of cineole increased significantly after damage (artificial or herbivore), but continued only when damage was sustained by herbivore feeding. Importantly, more cineole was emitted from high- than low-nutrient seedlings given an equivalent amount of damage. In the field, predation was significantly greater on model caterpillars baited with cineole than on unbaited models. 5. These findings are consistent with the hypothesis that any performance benefits insect herbivores derive from feeding on high-nutrient eucalypt foliage could be at least partially offset by an increased risk of predation or parasitism via increased emission of attractive volatiles.

Hunger-dependent and sex-specific antipredator behaviour of larvae of a size-dimorphic mosquito

Abstract: 1. Modification of behaviours in the presence of predators or predation cues is widespread among animals. The costs of a behavioural change in the presence of predators or predation cues depend on fitness effects of lost feeding opportunities and, especially when organisms are sexually dimorphic in size or timing of maturation, these costs are expected to differ between the sexes. 2. Larval Aedes triseriatus (Say) (Diptera: Culicidae) were used to test the hypothesis that behavioural responses of the sexes to predation cues have been selected differently due to different energy demands. 3. Even in the absence of water-borne predation cues, hungry females (the larger sex) spent more time browsing than did males, indicating a difference in energy needs. 4. In the presence of predation cues, well-fed larvae of both sexes reduced their activity more than did hungry larvae, and males shifted away from high-risk behaviours to a greater degree than did females, providing the first evidence of sex-specific antipredator behaviour in foraging mosquito larvae. 5. Because sexual size dimorphism is common across taxa, and energetic demands are probably correlated with size dimorphism, this research demonstrates the importance of investigating sex-specific behaviour and behavioural responses to enemies, and cautions against generalising results between sexes.