Showing papers in "Ecological Entomology in 1981"

Plant tannins and insect herbivores: an appraisal.

Abstract: . 1. The bioassays with tannins and insects, and the ecological studies on insects implicating tannins, are summarized and discussed. 2. Because of the great variation now shown in all aspects of the insect-tannin relationship, the difficulty of making generalizations is stressed. 3. The significance of plant tannins for insect herbivores is reconsidered in the light of recent work and little-known older work, which illustrate the very varied nature of its effects.

Foraging ecology of hoverflies: morphology of the mouthparts in relation to feeding on nectar and pollen in some common urban species

Abstract: . 1. Previous accounts of the feeding behaviour of hoverflies (Diptera: Syrphidae) are contradictory and in many cases do not correspond with field observations. 2. Patterns of feeding on nectar and pollen differ between species: these patterns are correlated with morphological differences. 3. The data indicate that there are two correlates of increasing tongue length: first, the proportion of pollen in the diet decreases; and second, the flies concentrate on visiting flowers with longer corollae, which contain more nectar sugar. 4. Reasons for these effects are discussed.

The sex ratio in ectoparasitic insects

Abstract: 1 The sex ratio in 379 collections, each consisting of more than 100 individuals, of 250 different species of ectoparasite belonging to seven orders of insects is recorded The data are gathered from a broad survey of published literature 2 In general, ectoparasitic insects emerge as adults in equal numbers of each sex, although there are certain exceptions 3 The sex ratio in natural populations may alter with numerous factors, but in general it is unbalanced, females usually predominating Out of 359 collections from the host's body or home, the sex ratio of 30% showed no significant departure from unity, 63% contained significantly more females, and 7% significantly more males 4 These imbalances could be due to sampling methods but this is rare Generally they are due to one sex, usually the male, being shorter lived than the other This may be because males are often more active and smaller than females, and thus more likely to be separated from the host's body or home, succumb to host predation, or be killed by adverse climatic or nutritional conditions

The sex ratio of ectoparasitic insects

Abstract: Abstract. 1. The sex ratio in 379 collections, each consisting of more than 100 individuals, of 250 different species of ectoparasite belonging to seven orders of insects is recorded. The data are gathered from a broad survey of published literature.

Intraspecific variability in herbivore performance and host quality: a field study of Uroleucon caligatum (Homoptera: Aphididae) and its Solidago hosts (Asteraceae)

Abstract: . 1. Performances of two clones of Uroleucon caligatum on eleven clones of Solidago were measured by caging aphids on plants in the field. 2. Several measures were obtained, including developmental time from birth to adulthood, size of first instar nymphs, adult weight, and total colony weight. 3. All measures of performance were strongly affected by plant clone. 4. Effect of aphid clone-plant clone interaction was significant only for first instar size. 5. In a subsequent screenhouse experiment, plant clones were subjected to uniform conditions and still exhibited large differences in host quality.

Habitat segregation among African treehole mosquitoes

Abstract: The division of macrohabitats, seasons and microhabitats among mosquitoes which inhabit water-filled treeholes was investigated in a wet/dry seasonal environment near the coast of Kenya. Twenty-two species from four genera &Aedes fourteen, Culex three, Eretmapodites three, Toxorhynchites two& were identified from treeholes and bamboo traps. These included five which were more abundant in other microhabitats: leaf axils, fruit husks, or abandoned snail shells. 2. Trapping in different vegetation zones or heights in forests revealed that all seventeen species examined showed oviposition preferences for one or more macrohabitats. Segregation of related species by macrohabitat was apparent among members of the subgenus Stegomyia of Aedes which accounted for 57% of individuals identified from one locality. 3. Seasonal overlap was low between Aedes, which tracked rainfall patterns, and Culex and Eretmapodites. Aedes bromeliae differed from other Aedes found in treeholes in that maximal larval numbers did not follow heavy rainfall. 4. Negative associations between Aedes fulgens and two congeners which co-occur in the same forest and season were attributed to preferences for tree- holes of different sizes. Positive associations between Aedes aegypti and several other Aedes were reduced when root buttresses, a subclass of larger treeholes containing more species, were removed. 5. Separation of species by growth stages may be accomplished by two schemes of egg hatching which desynchronize larval cohorts in the same tree- hole: the early pattern of Stegomyia whereby 50-95% of all eggs hatch at first immersion, and the delayed pattern of other subgenera &Diceromyia, Finlaya, Pseudarmigeres& in which less than one-third of all eggs hatch at first immersion. 6. The number of wet treeholes changed seasonally. During one year five or six periods occurred when 50% or more of the censused holes contained suffi- cient water for larval survival. The number of individuals and species of mos- quitoes in treeholes were positively correlated with treehole volume. In a com- parison of treeholes and theix mosquito fauna from two forests, treehole volume and mean number of species per hole differed significantly, but mosquito density did not. 7. Ecotonal trapping sites of mixed grasses, trees, and scrub yielded the highest mean numbers of species per sample, and traps placed outside a village, the lowest. Specific dominance was significantly less in the ecotone than else- where. The predatory larvae of Toxorhynchites brevipalpis in ecotonal and forested traps were not correlated with species richness.

The role of cereal growth stages and crowding in the induction of alatae in Sitobion avenae and its consequences for population growth

Abstract: . 1. Alatiform nymphs of Sitobion avenae were first recorded on wheat in 1977 and 1978 when there were 0.6 aphids per tiller and reached a maximum proportion of 0.9 of the population despite a seventeen-fold difference in aphid density between years. 2. At the same aphid density per tiller there was a higher proportion of alatiform nymphs on the tillers at an advanced than at an earlier stage of plant growth. 3. Both pre- and post-natal crowding, and late stages of plant growth, were important in inducing the development of alatae in the laboratory. 4. Changes in the quality of the host plant through its previously reported effect on reproductive and survival rates, and its effect on alate induction and emigration was important in shaping the population dynamics of S.avenae on cereals.

Effects of linear furanocoumarins on an adapted specialist insect (Papilio polyxenes).

Abstract: . 1. Examination of phytochemical literature reveals that a disproportionately large number of hostplants for species in the genus Papilio Section II, and in particular the machaon complex, contain linear furanocoumarins. 2. Although the linear furanocoumarin xanthotoxin is known to be toxic to generalist lepidopterous larvae, it failed to affect adversely the growth and survivorship of Papilio polyxenes, a member of the P.machaon complex that feeds primarily on Umbelliferae containing furanocoumarins, when incorporated into an artificial diet. 3. On the contrary, growth rate and weight gain were significantly improved in the presence of xanthotoxin. 4. It is proposed, based on this experimental evidence and on hostplant utilization patterns, that furanocoumarins play a significant role in the behavioural and biochemical adaptation of Papilio species to their umbelliferous hosts.

Adaptations to low temperature in high altitude insects from Mount Kenya

Abstract: . 1. The strategies for low temperature survival in insects on Mount Kenya were investigated. The insects were collected from their natural habitats and their supercooling points and low temperature tolerances determined. 2. Most insects showed no special adaptations to low temperature survival and seem to depend on spending the cold nights in protected habitats, such as beneath stones and fallen trunks of plants, as well as within the wet frills of dead leaves of alpine plants, where they are protected by the heat released from freezing water. 3. Some insects, e.g. Collembola, aphids and a curculionid beetle, which live in relatively unprotected habitats, had low supercooling points, allowing them to remain unfrozen when exposed to low night temperatures. A nucleator free diet is apparently essential for the survival of such species. 4. Two species of curculionid beetles were found to withstand freezing down to -7dC. These beetles had nucleating agents in their haemolymph and higher supercooling points than most of the other species studied. 5. A moderate freezing tolerance was found in larvae of a midge that lives in the watery liquid between the leaves of Senecio brassica.

Host plant associations, diversity and species—area relationships of mesophyll‐feeding leafhoppers of trees and shrubs in Britain

Abstract: . 1. Sixty-two British species of Typhlocybine leafhoppers are known to feed on the leaf-mesophyll tissue of trees and shrubs. British host records for fifty-five of these are given. 2. The leafhopper faunas of thirty-six species of native and introduced trees and shrubs are described. 3. The Shannon-Wiener equation was used to calculate species diversity for adult samples collected from twenty different species at sixteen different localities in Wales, southern England and northern Scotland. 4. Sorensen's coefficients were calculated for rearing data from Britain generally, and subjected to cluster analysis. Most trees have low similarities with respect to leafhopper faunas and are quite distinct. Taxonomic relationships of trees appear to be relatively unimportant in determining the similarities of their leaf-hopper faunas. 5. Using the same data, species—area relationships were calculated for thirty-four different tree and shrub species and their associated leaf-hoppers. A significant regression was obtained, but it explained only 16% of the variation. It is thus suggested that host plant range is relatively unimportant in determining the numbers of these species associated with different trees in Britain. 6. Some introduced species of trees, particularly the recently planted Nothofagus, have acquired large leafhopper faunas.

Some aspects of the rate of increase of a coccinellid

Abstract: . 1. Fecundity, growth and development were determined at a range of feeding levels and temperatures and compared with the component models for the predator rate of increase. 2. Fecundity and growth rate show a linear dependence on rate of consumption, while development rate conforms to an alternative non-linear model. The non-linearity of development rate is due to a dependence of weight gain during an instar on rate of consumption. 3. The primary influence of temperature is on the rate of consumption, limiting fecundity and growth rate at temperatures below the optimum for the stage, while higher temperatures have a deleterious effect. Temperature has a more direct influence on development rates, allowing comparable growth despite the variation in rates of consumption.

Spatial variations in egg density and the intensity of parasitism in a neotropical chrysomelid (Cephaloleia consanguinea)

Abstract: . 1 The chrysomelid beetle, Cephaloleia consanguinea (Hispinae), is a monophagous herbivore of Heliconia imbricata (Zingiberales: Heliconiaceae) in wet lowland forests of eastern Costa Rica. 2 Within the study area parasitism by eulophids and trichogrammatids (Hymenoptera: Chalcidoidea), the most common source of C. consanguinea egg mortality, varied in intensity from 35% to 50% during 1974–77. 3 Spatial relationships between the probability of parasitism and egg density per leaf were the net result of two opposing trends. The probability of at least one egg on an egg-bearing H. imbricata leaf being encountered and parasitized (here termed a ‘discovery’ of that leaf by parasitoids) increased significantly as egg density per leaf increased. The conditional probability of parasitism for other eggs present, given an attack on one egg, decreased with increasing egg density. 4 The net result was a decrease in the overall probability of parasitism as egg density per leaf increased. Host aggregation appears beneficial in reducing the intensity of parasitoid attacks. 5 Despite this inverse relationship between the overall probability of parasitism and egg density per leaf, a model based on the binomial distribution provides a good description of the spatial aspects of this host—parasitoid interaction.

The life cycles and age of Carabus glabratus Paykull and C.problematicus Herbst (Col.: Carabidae) on moorland in northern England

Abstract: . 1. The life cycles of C.glabratus and C.problematicus on moorland in northern England were studied in 1967. C.glabratus was a spring/summer breeder whilst C.problematicus was a late summer/autumn breeder and both had biennial life cycles. 2. Mandible wear and reproductive condition were used to indicate the age of the adults; some females lived for at least 2 years and probably three, with a distinct regression of their ovaries between each breeding season. 3. Mandible wear affected their ability to feed and thus build up fat reserves or develop eggs. Individuals with extreme mandible wear may die of starvation.

Host searching and oviposition behaviour of some parasitoids of aphidophagous Syrphidae

Abstract: 1 An analysis of host searching behaviour suggests that female parasitoids respond to aphid odours bringing them to the region of an aphid colony 2 Syrphid hosts are located within the aphid colony by response to contact chemicals on the larval integument 3 The behavioural mechanisms used by syrphid larvae to resist attacks and the subsequent responses made by parasitoids are described 4 Oviposition behaviour and host size preferences of parasitoids are described

Capture does affect probability of recapture in a butterfly species.

Abstract: In contrast to students of vertebrates (refs. in Southwood, 1978, p. 95) biologists who capture, mark, release and recapture invertebrates usually assume that their capture and marking techniques do not affect the subsequent behaviour of their study animals in ways which would invalidate use of the data for population size estimates. In many cases their confidence is supported by high recapture rates, with discrete populationstructures or ‘traplining’ phenomena (Refs. in Gilbert & Singer, 1975). Where recapture rates are low, however, data may be considered ‘poor’ and remain unpublished, or authors may infer extremely low survival rates, as did Cook er al. (1971), working with neotropical Papilionid butterflies of the genus Parides. Like these authors, we also obtained low recapture rates for a tropical Papilionid, Graphium sarpedon L. marked in Gunong Mulu National Park, Sarawak. About 2% of butterflies captured, marked and immediately released were recaptured on subsequent daysflable 1). Such alow recapture rate could be due to: (1) large population size or low survival; ( 2 ) directional migration; (3) ‘periodicity in availability of subcategories’ (Southwood, 1978, p. 95) which in this case could result from intermittent need of individuals for the resource at the site of capture; this site was a riverside beach where the butterflies were ‘puddling’ (Arms at al., 1974); (4) changes in behaviour of the insects as a result of marking; (5) changes in behaviour of the insects as a result of capture. In this case we were able to show experimentally that explanations in category (5 )

Why a cicada, Mogannia minuta Matsumura, became a pest of sugarcane: an hypothesis based on the theory of ‘escape’

Abstract: . 1. Life tables were constructed for natural populations of a cicada. Mogannia minuta, during an outbreak in sugarcane fields at Okinawa to determine possible reasons for the outbreak. 2. The highest mortality during the life cycle was during the beginning of the nymphal stage, and was mainly due to predation by ants. 3. The estimated rate of natural increase based on a survivorship—fecundity schedule in sugarcane fields was near unity, but during the increasing period the rate was estimated to be substantially higher than unity. 4. The rate of natural increase in Miscanthus-grassland was slightly negative, suggesting that the grassland population was maintained by immigration of adults from sugarcane fields. 5. Escape from predation may be the main cause of the special distribution pattern and the maintenance of extraordinarily high densities for many years.

Physiological correlates of the availability of Glossina morsitans centralis Machado to different sampling methods

Abstract: . 1 The feeding cycle for male tsetse flies and the pregnancy cycle for females are used as frameworks for investigating the field behaviour of Glossina morsitans centralis Machado in Zambia, and hence the sampling biases of different capture devices. 2 Flies were collected in the field using hand nets and an electric back pack on foot patrols, and hand nets, hand-catching and an electric screen on landrover patrols. They were analysed for wing-fray, vein-length, chloroform-extractable fat and haematin. In addition, samples of laboratory-bred females killed daily during their second pregnancy cycle were analysed for the last two parameters. 3 The daily flying time of males is estimated from the fat—haematin curve to be about 32 min/day, which is identical to previous estimates for G. morsitans from Tanzania. 4 From the varying numbers and fat content of male flies caught by the different sampling methods during the course of the feeding cycle it is concluded that both haematin levels and fat reserves influence fly behaviour. 5 Comparison of the frequency distribution of wild-caught and laboratory-bred females along the corrected residual dry weight axis of the pregnancy cycle suggests that the results of combined electric-trap and hand-net sampling reflect the actual frequency distribution in the wild population at least for the first 7 days of the pregnancy cycle; but females in the last 2 days of their pregnancy cycle are apparently unavailable to sampling devices, perhaps because of their reduced flight activity. 6 The very variable percentage female catch (10.9–43.4%) returned by the different sampling methods is discussed in the light of the detailed analysis of the differential availability of male and female flies to each capture device.

Effects of voltinism, interspecific competition and parasitism on the population dynamics of the hemlock scales, Fiorinia externa and Tsugaspidiotus tsugae (Homoptera: Diaspididae)

Abstract: . 1 Life tables were constructed for solitary and coexisting populations of univoltine Fiorinia externa Ferris and bivoltine Tsugaspidiotus tsugae (Marlatt) (Homoptera: Diaspididae), two exotic scale pests of eastern hemlock, Tsuga canadensis Carriere, in the northeastern United States. 2 Solitary and coexisting populations of F. externa had similar survivorship and population growth rates resulting in an annual increase in density of 7–16%. Survivorship of solitary and coexisting populations of T. tsugae also was similar, but growth rates differed substantially. While solitary populations increased their density by 68% annually, populations coexisting with F. extema were reduced 74% each year. 3 The annual reduction in T. tsugae density where it coexists with F. externa was due in part to interspecific competition which resulted in higher mortality to nymphs from dispersal and starvation and in lower fecundity of adult females relative to solitary populations. A host shift by the parasitoid, Aspidiotiphagus citrinus (Crawford) (Hymenoptera: Aphenlinidae) from F. externa to T. tsugae in autumn also accounted for 71% of the annual decrease in T. tsugae numbers. Therefore, F. externa adversely affects the growth of T. tsugae populations not only because of its superior competitive ability but also because adult para-sitoids which emerge from it subsequently attack nymphs of T. tsugae in autumn. 4 Parasitism and starvation of nymphs resulting from competition were the key mortality factors in the population dynamics of these exotic hemlock scales.

Adult Lepidop tera ‘feeding’ at withered Heliotropium plants (Boraginaceae) in East Africa

Abstract: There are several records, mainly anecdotal, of adult Lepidoptera ‘feeding’ at withered plants containing pyrrolizidine alkaloids (PAS) as secondary substances. Most records come from Asia, America and Australia (e.g. Morrell, 1955; Pliske, 1975; Goss, 1979; Edgar, 1975). From Africa only two Danainae (Amauris niavius and Danaus chrysippus) have been reported to ‘feed’ at withered Heliotropium (Sevastopulo, 1969; Owen, 1971; Schneider et al., 1975). In the course of two safaris in Kenya, East Africa, in 1979 and 1980 I conducted baiting experiments with withered plant material in various habitats in order to search for further African species of Lepidoptera attracted to such plants. Entire plants of various species of Heliotropium (Boraginaceae) (mainly H.pectinatum Vaupel, H.steudneri Vatke, H.indicum L., H.gorinii Chiv.) were air-dried and subsequently used as baits. About 20 g of the plant material, usually kept in nylon gauze bags, was placed either on the ground (Figs. 1 and 3), in bushes, or in hanging traps (Fig. 2). In all, twenty-seven species of Lepidoptera representing the families Arctiidae (sixteen ssp.), Ctenuchiidae (two ssp.) and Danainae (nine ssp.) were found attracted to and ‘feeding’ at the withered Heliotropiurn (Table 1). Also, males only of a new species of chrysomelid’ beetle of the genus Gabonia visited the baits at dusk (Boppre & Scherer, 1981). Various other moths (mainly Pyralidae) were occasionally found at the baits but since these came in small numbers and appeared disorientated, specific attraction is

The adaptive and evolutionary significance of wing polymorphism and parthenogenesis in Ptinella Motschulsky (Coleoptera: Ptiliidae)

Abstract: . 1The incidence of wing polymorphism varies seasonally in field populations of Ptinella aptera and Ptinella errabunda with alatae increasing in abundance in summer. 2In laboratory cultures of P. aptera alate development varies with temperature. This implies that morph determination is based on a physiological switch sensitive to temperature and possibly other adaptively relevant environmental factors. 3Alate P. aptera produce a higher proportion of alate offspring than do apterous parents suggesting an inherited component in polymorphism control, or some form of maternal effect. 4The female biased sex ratio expected of a regularly inbreeding species was found only in the alate morph. Apterous beetles show a 1:1 sex ratio which is explained by the females' limited capacity to store sperm, the enormous size of the sperm, and the consequent need for multiple insemination. 5Ptinella errabunda is thelytokous but fails to realize the potentially doubled fecundity associated with parthenogenesis. Both the number of eggs produced and their viability is lower than in bisexual congeners. 6Enhanced colonizing ability, rather than energy economy, is considered to be the most important selective advantage of parthenogenesis to Ptinella in the subcortical habitat. 7The spatial and temporal heterogeneity of the subcortical habitat is considered to have favoured the evolution and maintenance of parthenogenesis and wing polymorphism in Ptinella.

The influence of age and season on dispersal and recapture of Anopheles culicifacies in Sri Lanka

Abstract: . 1. Three mark—release—recapture experiments with Anopheles culicifacies were carried out at different seasons in Sri Lanka. Blood fed females were collected daily in cattle baited huts, marked with fluorescent powder and released in the same village. In two of the experiments males and females were reared, marked when newly emerged, and released. The recapture rates were recorded in the same village and in a second village 2 km away. 2. The mosquitoes marked when already mature yielded an estimate that 2–7% of the mosquitoes in the second village had flown from the first. The recapture rate of reared mosquitoes in the first village was much lower than with those marked when already mature. This difference could be at least partly attributed to a tendency to disperse when young, as shown by the considerable number of recaptures of young mosquitoes in the second village. 3. By varying the colour used for marking, estimates were made of the amount of dispersal from hut to hut in the first village, the daily survival rate and the proportion of the wild population resting in the collecting huts each day. 4. Using the latter two estimates equations have been solved predicting the rate of build-up of the proportion of recaptures. These predictions were compared with the observed results. The data on dispersal are discussed in relation to possible method for delaying the build-up of insecticide resistance.

Host tree influences on the dispersal of first instar gypsy moths, Lymantria dispar (L.)

Abstract: . 1. In laboratory tests, first instar gypsy moths attempted dispersal more frequency when exposed to less acceptable foliage. 2. First instars from small eggs attempted dispersal less frequently than larvae from large eggs when exposed to foliage from highly acceptable or marginally acceptable hosts. Dispersal rates of larvae from medium sized eggs were intermediate. 3. These results (1–2) confirm and expand upon the findings of Capinera & Barbosa (1976). 4. In the field, data on the relative densities of larvae on different host species support the conclusion that the frequency of dispersal attempts is inversely related to host acceptability. 5. The implications of these findings for the population dynamics of the gypsy moth are discussed.

Colour patterns of Syrphidae. III. Sexual dimorphism in Eristalis arbustorum

Abstract: . 1. The hoverfly Eristalis arbustorum L. (Diptera, Syrphidae) is a sexually dimorphic Batesian mimic of bees and wasps. 2. This dual mimicry entails good mimicry of several small, dark bees (mainly mining bees) by female E.arbustorum, and less specific mimicry of wasps and other yellow and black Hymenoptera by males. 3. There is also variability of colour pattern within both sexes of E.arbustorum. 4. Seasonal fluctuations in the pattern frequencies of males occur because the temperature during pupal development influences the coloration of the adult. 5. Temporal changes in the pattern frequencies of females are attributable to developmental darkening of the abdomen. 6. These effects can be explained by the fact that the phenotypic requirements for thermoregulation and protection against predation will be different for males and females, and will also vary with time. 7. Behavioural differences between males and females are a component of the sexual dimorphism in this species.

Population fluctuations of mosquitoes in the non-seasonal tropics.

Abstract: . 1 Seasonal and annual fluctuations in abundance of a number of species of mosquitoes were studied in a relatively non-seasonal climate near Almirante, Panama. 2 The fluctuations observed were large, but did not have a period of 1 year and should be classified as non-seasonal. 3 At each site the various species were not synchronous in their fluctuation pattern, but the fluctuations of each species were synchronous over an area of at least 4 km long, in spite of large differences in habitat. 4 Changes in abundance from year to year observed in these mosquitoes are large compared with those of insects, including mosquitoes, in other areas of Panama. 5 The importance of such large and unpredictable fluctuations in abundance for planning control measures is discussed.

An ecological interaction between citrus fruit, Penicillium moulds and Drosophila immigrans Sturtevant (Diptera: Drosophilidae)

Abstract: . 1. Potential Drosophila breeding sites were collected from a fruit market, and the adults allowed to emerge from them. 2. D.immigrans and D.melanogaster were the species with the highest frequency of emergences from citrus fruit. 3. D.immigrans was especially associated with citrus fruits infected with Penicillium italicum or P.digitatum, two specialist moulds of citrus. D.melanogaster was more often found in uninfected fruit. 4. In the laboratory D.immigrans larvae survived better than D.melanogaster larvae on Penicillium-infected citrus fruit. 5. These adaptations suggest that D.immigrans may have originally evolved as a citrus specialist, becoming a domestic species as these fruits were exploited commercially.

Patterns of Abundance, Distribution, and Alary Polymorphism among the Salt Marsh Delphacidae (Homoptera: Fulgoroidea) of Northwest Florida

Abstract: . 1. The species of Delphacidae captured in nearly 16000 sweeps of salt marsh vegetation in Northwest Florida, U.S.A., are examined. Individuals belonging to fourteen species were captured during the 15-month study, a somewhat larger number than is found in most locations. 2. Abundances ranged from one to 1064 individuals per species. The abundances, habitat preferences, and patterns in wing-polymorphism among the species collected were similar to those reported previously from other locations, but important differences were found which reflect the vegetational composition typical of our study area. 3. Wing-morph ratio differences between delphacid populations may reflect strategies for dealing with differences in stability and distribution of their respective habitats. The ratio of macropter/brachypter individuals in various populations of delphacids investigated correlates with the probability that a dispersing individual will find a more suitable habitat patch. The phenomenon is illustrated with a comparison of wing-morph ratios in populations of Prokelisia marginata (Van Duzee) from locations which differ in the extent, distribution, and stability of their stands of Spartina alterniflora Loisl. (smooth cordgrass), the common host of P.marginata. 4. Macroptery is favoured in Atlantic Coast marshes, where habitat patches are differentially suitable, but extensive and predictable. The probability of finding a better patch by dispersing is therefore high. 5. Brachyptery predominates at Cedar Key, Florida, where habitat patches are extensive, stable, and equally suitable during most of the year; and at St Marks, Florida, where resource patches are small, infrequent, isolated, and regularly disturbed. Under these conditions, the probability of finding a better patch by dispersal is low. 6. The conditions at St Marks may have promoted a local host expansion by P.marginata at this location.

The effect of temperature on the growth and reproduction of two closely related aphid species on sycamore

Abstract: . 1. Egg hatch in the two species of sycamore aphid was temporally separated: the median time to hatch was 30 days later in Drepanosiphum acerinum than in D.platanoidis. 2. D.platanoidis was larger at egg hatch than D.acerinum. Progeny of D.platanoidis adults were also larger than those of D.acerinum. 3. D.platanoidis was the larger of the two species as an adult, as a consequence of its greater birth weight. 4. Over a range of temperatures, development rates in the two species were the same, while the growth rate in D.acerinum was significantly higher at high temperatures. 5. The reproductive rate of the two species was significantly different at 6dC and 20dC.

Nest construction and larval behaviour of Bubas bison (L.) and Bubas bubalus (01.) (Coleoptera, Scarabaeidae)

Abstract: . 1 Female beetles working alone or in cooperation with a male excavated vertical, tunnel-shaped brood chambers. Each chamber was filled with dung to form a cylindrical brood mass which contained two eggs, one near each pole. 2 To examine the possible relationship with other Onitini (which lay either one or several eggs per brood mass) factors that influence the two-egg programme were studied. Brood masses with only a single egg were formed if excavation was resumed prematurely. Conversely, when excavation was suppressed several oviposition programmes fused to produce a multi-egg brood mass. 3 The larvae repaired their chambers in the typical Scarabaeine manner by building a self-supporting wall formed from their own excrement. This behaviour also prevented direct contact and fighting between adjacent larvae in the same brood mass, and it allowed the larvae to survive inside artificial brood balls. Similar behaviour was observed in larvae of Onthophagus taunts and Ontho-phagus vacca (which develop in one-egg brood masses). The evolution of nesting habits that involve multi-egg brood masses or free-standing brood balls may depend on the pre-existence of this larval repair behaviour.

A 9-year study of the life cycle of Ephemera danica Müll. (Ephemeridae: Ephemeroptera) in the River Lambourn, England

Abstract: . 1. The life cycle of the mayfly, Ephemera danica, was studied on two contrasted sites on the River Lambourn between 1971 and 1979. 2. Quantitative samples of nymphs were taken on the five major biotopes of the river bed, gravel, silt, Ranunculus, Berula and Callitriche. Exposed areas of gravel and silt held significantly lower densities of nymphs than the three macro-phytes with their underlying substrata. The sandy substratum underlying beds of Berula frequently held significantly higher densities than the other macrophytes. 3. Monthly samples from March 1971 to April 1972 followed by samples in June and December from 1972 to 1979 indicated that the nymphal phase normally took 2 years in the River Lambourn. 4. All odd-numbered years from 1971 to 1979 produced weak year-classes. In contrast, all even-numbered years between 1970 and 1978, with the exception of 1972, produced relatively strong year-classes. 5. Meteorological data for the period of flight activity in E.danica indicated that conditions were colder and damper in 1972 than in the other even-numbered years of the study, when recruitment was more successful.

Successful and unsuccessful development of colonies of Vespula vulgaris (Linn.) (Hymenoptera: Vespidae)

Abstract: . 1 Six categories of immature and five categories of mature colonies are described and their developmental relationships suggested. 2 Mature brood destroyed by the workers became numerous in 46.4% of the immature colonies. Most of these formed unsuccessful colonies (36.9%) producing few or no queens. The remaining 9.5% recovered to form successful colonies. 3 Successful colonies either reared queens only (mean 356 queens), or queens (mean 1461) and males (mean 254) in their large cells. 4 The number of small cells in mature colonies correlated with the number of cells built by the founder queen. 5 The greater the number of large cells in a mature colony the greater were the chances that a larger proportion of these cells would be used to rear adults. 6 The number of small and large cells are correlated in mature successful colonies. 7 Queen activity and quality are important factors in the control of colony size and success. 8 Selective destruction of male sealed brood in the large cells is linked to worker, rather than queen, control.