Showing papers on "Aphid published in 1990"
TL;DR: Host-mediated interactions were explored for two aphid species that feed on plants of the genus Cheno- podium that shared a common resource, the phloem sap of their host, and results emerged that resistance to leaf-galling aphids is not correlated with resistance to root-feeding aphids in this system.
Abstract: While the competitive interactions of herbivores are often debated, rarely have the resistance traits of their host plants been considered as an important factor that might determine the outcome of an interaction. In the study reported here, host-mediated interactions were explored for two aphid species that feed on plants of the genus Cheno- podium. Pemphigus betae feeds underground on roots, while Hayhurstia atriplicis feeds aboveground where it forms leaf galls. Although they never encountered one another directly, these two aphid species shared a common resource, the phloem sap of their host. We examined the effects of each of these herbivore species on their host plants and on one another through several garden and growth chamber experiments. Four major results emerged. First, the root-feeding aphid P. betae had no significant effects on its hosts. In contrast, leaf galling by H. atriplicis reduced overall host mass by an average of 54% and seed set by an average of 60%. Second, competitive interactions between the herbivore species depended on the level of host resistance to leaf galling by H. atriplicis. On susceptible plants, leaf-galling colonies of H. atriplicis reduced P. betae numbers by an average of 9 1%, often eliminating the root feeders entirely. In contrast, on plants resistant to galling, H. atriplic is were smaller and did not affect P. betae infesting roots of the same hosts. Third, the interaction was asymmetrical; although H. atriplicis had a strong negative effect on P. betae, the latter showed no measurable effects on H. atriplicis. Censuses indicated that the strong negative effects of H. atriplicis on P. betae, as found in the growth chamber and garden experiments, also take place naturally in the field. Fourth, although one might expect plants resistant to one aphid species to be resistant to other aphids also, resistance to leaf-galling aphids is not correlated with resistance to root-feeding aphids in this system.
194 citations
TL;DR: Results show that individual aphid genotypes possess the ability to adaptively modify their escape behaviour with changes in prevailing conditions, and are less likely to drop or walk in response to pheromone when feeding on high quality than on low quality hosts.
Abstract: Pea aphids have several alternative responses to the detection of alarm pheromone produced by conspecifics. One of these, dropping from the feeding site to the ground, is potentially costly owing to the risk of desiccation-induced mortality on the ground before another host plant can be reached. Both dropping and walking from the feeding site incur a cost due to lost feeding opportunity. The aphids' decision as to which anti-predator tactic to use should be sensitive to the costs of their behaviour. Consequently, aphids should be less likely to drop when the risk of desiccation is higher, and less likely to drop or walk when the lost opportunity cost is higher. We tested these predictions by manipulating climatic severity (temperature and humidity) and host quality, respectively. As predicted, aphids are less likely to drop or walk in response to pheromone when feeding on high quality than on low quality hosts, and less likely to drop when the environment is hot and dry than when it is more benign. The latter is true whether the aphids are feeding on real or simulated leaves. Since all aphids were of the same clone, these results show that individual aphid genotypes possess the ability to adaptively modify their escape behaviour with changes in prevailing conditions. A number of other behavioural observations in the aphid literature may be interpreted in an economic or cost-benefit framework. The approach holds considerable promise for understanding many aspects of the anti-predator behaviour of aphids and other animals.
143 citations
Book•
01 Oct 1990
TL;DR: Aphid-Plant genotype interactions-perspective, a model system for the study of phytotoxic homoptera, and molecular interactions of intracellular symbionts and aphids.
Abstract: Aphid-Plant genotype interactions-perspective (H.F. van Emden). Ecological interactions of aphids and their host plants (A.F.G. Dixon). Aphid host plant ecology: The bird cherry-oat aphid as a model (S. Wiktelius et al). Experimental studies on some aphid life-cycle patterns and the hybridization of two sibling species (G.X. Zhang, T.S. Zhong). The population biological consequences of a mosaic-like population structure in Macrosiphum rosae (K. Wohrmann, J. Tomiuk). The use of restriction fragment length polymorphisms to study the ecology and evolutionary biology of aphid-plant interactions (K.N. Paige et al). Continuous recording of stylet penetration activities by aphids (W.F. Tjallingii). Aphid stylet movement and host-plant reaction in the case of adelgidae on spruce (O. Rohfritsch). Resistance mechanisms of plant genotypes to various aphid species (P. Harrewijn). Aphid salivary secretions and their involvement in plant toxicoses (P.W. Miles). The role of plant matrix polysaccharides in aphid-plant interactions (B.C. Campbell, D.L. Dreyer). Greenbugs and wheat: A model system for the study of phytotoxic homoptera (J.D. Ryan et al). The role of secondary plant compounds in aphid-host interactions (H.M. Niemeyer). Lipids at the aphid-plant interface (J.W. Dillwith , R.C. Berberet). Aphid induced alteration of the availability and form of nitrogenous compounds in plants (K.W. Dorschner). Pea aphid biotypes in relation to plant genotypes and chemically defined diets (P.N. Srivastava, J.L. Auclair). Specificity in aphid/plant genetic interactions, with particular attention to the role of the alate colonizer (R.L. Blackman). Genetic stability in aphid clones and its implication for host-plant interactions (J. Tomiuk). Sexual reproduction and inheritance of virulence in the greenbug, Schizaphis graminum (Rondani) (G.J. Puterka, D.C. Peters). Nutritional interactions between Myzus persicae and its symbionts (A.E. Douglas). Partial characterization of the ribosomal RNA operons of the pea-aphid endosymbionts: Evolutionary and physiological implications (B.M. Unterman, P. Baumann). Molecular interactions of intracellular symbionts and aphids (H. Ishikawa). Index.
141 citations
TL;DR: Observed patterns of preference by Aphelinus females for particular aphid species and instars reflect the outcome of behavioral interactions between the hosts and the parasites, rather than preference in the strict sense.
Abstract: The parasite Aphelinus asychisWalker (Hymenoptera: Aphelinidae) oviposits in all four instars of the pea aphid, Acyrthosiphon pisum(Harris) (Homoptera: Aphididae). Searching females display a highly stereotyped sequence of behaviors when encountering a host. Once recognized, an aphid is examined and probed by the wasp with the everted ovipositor prior to oviposition. Oviposition success is influenced by aphid behavior that is related to aphid size and expressed through instarspecific escape and defense reactions. Being smaller and less able to defend themselves, first and early-second instars of pea aphid are more susceptible to successful parasitism than third and fourth instars, in that order. Observed patterns of preference by Aphelinus females for particular aphid species and instars reflect the outcome of behavioral interactions between the hosts and the parasites, rather than preference in the strict sense.
124 citations
TL;DR: Polyphagous predator densities were manipulated in a wheat crop using polythene exclusion barriers to increase the likelihood of predator capture and decrease the chance of prey capture.
Abstract: 1 Polyphagous predator densities were manipulated in a wheat crop using polythene exclusion barriers
2 The rates at which aphids fell to the ground and subsequently climbed and returned to the crop canopy were measured
3 Peak aphid density was highest when polyphagous predator density was lowest
4 Similar rates of aphid fall-off were measured in each plot, but aphid climbing rate was highest when predator densities were lowest
5 It was concluded that ground-zone predators reduced the rate at which aphids return to the crop canopy
124 citations
TL;DR: It is suggested that these chemical differences may be related to interactions among the broad feeding tactics of sucking or chewing milkweed leaves, life history constraints of holometabolyversus hemimetaboly, the distribution of milkweed food resources in space and time, and the dynamics of natural enemies.
Abstract: Cardenolide sequestration by a hemimetabolous aphid and a holometabolous butterfly from the neotropical milkweed,Asclepias curassavica L., is compared. The oleander aphid,Aphis nerii B. de F., sequestered a similarly narrow range of cardenolide concentrations to the monarch butterfly,Danaus plexippus (L.), from the wide range of concentrations available in leaves of A.curassavica. However, A.nerii sequestered significantly less cardenolide (269 µg/0.1 g) thanD. plexippus (528 µg/0.1 g). The honeydew excreted by A.nerii was comprised of 46% cardenolide. The complete polarity range of 25 cardenolides detected by thin layer chromatography in A.curassavica was represented in the 17 whole aphid cardenolides and the 20 aphid honeydew cardenolides detected. D.plexippus sequestered a narrower polarity range of 11 cardenolides, having eliminated low polarity cardenolide genins and glycosides. It is suggested that these chemical differences may be related to interactions among the broad feeding tactics of sucking or chewing milkweed leaves, life history constraints of holometabolyversus hemimetaboly, the distribution of milkweed food resources in space and time, and the dynamics of natural enemies.
94 citations
TL;DR: A four-year field survey of wheat, barley, and corn generated data on 10 species of fungal pathogens, including eight Entomophthorales and two Hyphomycetes recovered from 2,930 cadavers of aphids infesting grains grown under irrigation in southwestern Idaho, finding P. neoaphidis was the most prevalent species annually in populations of M. noxia and also frequently infected other hosts.
Abstract: A four-year field survey of wheat, barley, and corn generated data on 10 species of fungal pathogens, including eight Entomophthorales and two Hyphomycetes recovered from 2,930 cadavers of aphids infesting grains grown under irrigation in southwestern Idaho. Seven species of cereal aphids, including the Russian wheat aphid, Diuraphis noxia (Mordvilko); the potato aphid, Macrosiphum euphorbiae (Thomas); Metopolophium dirhodum (Walker); the corn leaf aphid, Rhopalosiphum maidis (Fitch); the bird-cherry oat aphid, R. padi (L.); the greenbug, Schizaphis graminum (Rondani); and the English grain aphid, Sitobion avenae (F.), were recorded as hostsof one or more species of entomopathogenic fungi. The fungi were identified as Pandora neoaphidis (Remaudiere & Hennebert) Humber, Conidiobolus obscurus (Hall & Dunn) Remaudiere & Keller, C. coronatus (Costantin), C. thromboides Drechsler, Entomophthora chromaphidis Burger & Swain, Neozygites fresenii (Nowakowski) Remaudiere & Keller, Zoophthora radicans (Brefeld) Batko, Z. occidentalis (Thaxter) Batko, Beauveria bassiana (Balsamo) Vuillemin, and Verticillium lecanii (Zimmermann) Viegas. P. neoaphidis was the most prevalent species annually in populations of M. dirhodum and D. noxia and also frequently infected other hosts. Conidiobolus spp. were secondary to P. neoaphidis in occurrence, commonly infecting several aphid species. E. chromaphidis, N. fresenii, Z. radicans , and Z. occidentalis were recovered only occasionally and on fewer aphid species. Two Hyphomycetes, B. bassiana and V. lecanii , infected aphids in the field at very low levels compared with the Entomophthorales. All species, except N. fresenii and Z. occidentalis , were isolated from their aphid hosts with agar media (SDAY or SEMA, or both) or liquid insect tissue culture medium.
90 citations
TL;DR: In galls with experimentally manipulated numbers of soldiers and non-soldiers, it was clearly shown that it is the soldiers alone that kill the predators (Anthocoris minki and 1st instar Adalia bipunctata) (see Table 3).
Abstract: The thick-legged first instar soldiers of the gall-forming aphid Pemphigus spyrothecae Pass. are able to protect the aphids in the gall from being eaten by a range of insect predators. In artificial galls, the soldier aphids were able to kill first instar ladybirds Adalia bipunctata (L.) (Coleoptera: Coccinellidae), early third instar hoverfly larvae Eupeodes (Metasyrphus) corollae (Fab.) (Diptera: Syrphidae), and first-third instar Anthocoris nemoralis (Fab.) (Hemiptera: Cimicidae). Almost all the aphids that attacked the predators were themselves killed. The soldiers were also able to kill predators introduced into natural galls. Experiments were devised in which individuals of Anthocoris minki, which is the most important insect predator of the gall generations of Pemphigus at the study site, were free to enter and leave the gall: the soldiers were effective both in preventing the predator's access to the gall and in killing those predators that did manage to get in. In galls with experimentally manipulated numbers of soldiers and non-soldiers, it was clearly shown that it is the soldiers alone that kill the predators (Anthocoris minki and 1st instar Adalia bipunctata) (see Table 3). Even though many soldiers may die during these encounters, the selective advantage of killing the predators is high, since observations show that individual A. minki can pass through more than one instar inside a gall and kill all the aphids therein. The aphids were not observed to attack conspecific aphids from other galls or the cohabiting aphid Chaitophorus leucomelas Koch. The primary role of the soldier caste is therefore the defence of the aphid colony against predators.
86 citations
TL;DR: Type B trichome exudate of the S. berthaultii accession PI 473331 is composed of a complex of 3′,3,4,6-tetra-O-acyl sucroses containing primarily short-chain branched carboxylic acids.
Abstract: Removal of type B trichome exudate fromSolanum berthaultii leaflets leads to a decrease in tarsal gumming and mortality and an increase in feeding by the green peach aphid,Myzus persicae. Type B trichome exudate of theS. berthaultii accession PI 473331 is composed of a complex of 3′,3,4,6-tetra-O-acyl sucroses containing primarily short-chain branched carboxylic acids. The acyl constituents are primarily derived from 2-methylpropanoic, 2-methylbutyric, and 8-methylnonanoic acids but constituents derived fromn-decanoic and dodecanoic acids are also present. Sucrose esters inhibit settling and probing by aphids in glass feeding cages.
86 citations
TL;DR: Amounts of asparagine and glutamine were smaller in the honeydew of symbiotic adults than in that of sterile, aposymbiotic adults at the same age, suggesting that these amino acids were utilized efficiently by symbiotic aphids.
79 citations
TL;DR: Using observed temperatures and phenological models from the literature, it is determined that C. maculata has the potential to complete two or three generations per year in Rhode Island and three or four generations peryear in Michigan.
Abstract: The polyphagous coccinellid Coleomegilla maculate DeGeer fed on eggs and small larvae of the Colorado potato beetle, Leptinotarsa decemlineata (Say). Prey consumption rates were highly correlated with temperature. This predator did not prefer aphids over potato beetle larvae in choice tests, but consumption of larvae decreased as aphid densities increased. Field cage studies demonstrated that C. maculata adults can significantly reduce populations of Colorado potato beetle eggs and small larvae. The incidence of C. maculata adults was monitored in early- and late-planted potatoes ( Solanum tuberosum ) in Rhode Island and Michigan. This predator coincided with first-generation Colorado potato beetle prey in early-planted potatoes in both states and with second-generation potato beetle prey in late-planted potatoes in Rhode Island. C. maculata also was found in cole crops, snap beans, cucurbits, and sweet corn in 1986 and in alfalfa and sweet corn in 1987, and the highest densities were observed in sweet corn during pollen production. Using observed temperatures and phenological models from the literature, we determined that C. maculata has the potential to complete two or three generations per year in Rhode Island and three or four generations per year in Michigan. The actual number of generations is probably dependent on its residence and dynamics in several adjacent crops.
TL;DR: There was a significant negative relationship between the concentration of sugar esters on the leaf and the level of potato aphid infestation in a segregating L. esculentum × L. pannellii F2 population.
Abstract: Behavioral studies have shown that aphid resistance in Lycopersicon pennellii (Corr.) D'Arcy is due to the presence of sugar esters in glandular exudate of the type IV trichomes. In this study, various methods for the estimation of epicuticular sugar ester concentrations were examined. There was a significant negative relationship between the concentration of sugar esters on the leaf and the level of potato aphid infestation in a segregating L. esculentum × L. pannellii F2 population. Selection for sugar ester accumulation should be an efficient selection technique for the aphid resistance of L. pennellii and other species that synthesize epicuticular sugar esters. The wild Peruvian tomato species (Lycopersicon pennellii (Corr.) D'Arcy) is a potential source of resistance to insects and other phytophagous pests of the cultivated tomato (L. esculen- tum Mill.) (de Ponti et al., 1975; Georgia and Sotirova, 1978; Gentile and Stoner, 1968a, 1968b; Gentile et al., 1968; Gentile et al., 1969; Goffreda et al., 1988; Juvik et al., 1982), Potato aphid (Macrosiphum euphorbiae Thomas) resistance in L. pen- nellii is related to the presence of glucose esters in type IV trichome exudate (Goffreda, 1988; Goffreda et al., 1989). The 2,3,4-tri-O-acylglucoses of L. pennellii are composed of C 4 to Cl2 fatty acids, including 2-methylpropanoic, 2-methylbutan - oic, 3-methylbutanoic, 8-methylnonano ic, n-decanoic, and n- dodecanoic acids (Burke et al., 1987). In laboratory bioassays, purified glucose esters significantly deter aphid settling at con- centrations as low as 25 µg·cm -2 ; at concentrations of 100 µm·cm -2
TL;DR: The patterns of host‐feeding and oviposition were examined in Aphelinus asychis Walker, which had been provided with second‐instar pea aphids as hosts.
Abstract: . 1. The patterns of host-feeding and oviposition were examined in Aphelinus asychis Walker, which had been provided with second-instar pea aphids as hosts.
2. Female wasps responded to increasing host density (between one and forty aphids for 24 h) with an increasing tendency to oviposit rather than to feed. Superparasitism occurred at all aphid densities, even when unparasitized aphids were available.
3. Aphids intended for feeding were paralysed and died. Wasps did not feed on and oviposit in the same aphid.
4. Feeding to satiation lasted between 4 min and 42 min. Females that had starved for ≰18 h generally deposited one or more eggs before feeding again, while the reverse was true in wasps that had starved for 21 h.
5. The host-feeding behaviour of A. asychis is determined by a female's nutritional status. At low rates of host encounter, the anhydropic eggs may be resorbed. This reproductive strategy conforms to the destructive non-concurrent type among the Hymenoptera.
TL;DR: An isolate of Beauveria bassiana (SGBB8601) and Verticillium lecanii (DNVL8701) were bioassayed against six species of globally distributed cereal-infesting aphids under controlled conditions as mentioned in this paper.
Abstract: An aphid-derived isolate of Beauveria bassiana (SGBB8601) and Verticillium lecanii (DNVL8701) were bioassayed against six species of globally distributed cereal-infesting aphids under controlled conditions. Aphids were immersed in conidial suspensions at concentrations ranging from 104 to 108 conidia/ml, each concentration being replicated six times with 20 aphids treated per replicate. Pathogenicity of both fungal species was confirmed on all the aphids tested, but in most cases, B. bassiana was more virulent than V. lecanii . The LC50 values for B. bassiana and V. lecanii were 8.2 × 104 and 4.1 × 105 conidia/ml, respectively, on Diuraphis noxia ; 2.1 × 105 and 9.8 × 105 on Schizaphis graminum ; 3.3 × 105 and 7.0 × 105 on Metapolophium dirhodum ; 1.1 × 105 and 1.3 × 106 on Sitobion avenae ; 2.1 × 106 and 8.9 × 105 on Rhopalosiphum maidis ; and 3.3 × 106 and 6.9 × 106 on R. padi . Statistical analysis indicated that there were substantial differences in susceptibility to the two pathogens and in virulence of each fungus to different aphid species. The LT50 values at all concentrations varied between the pathogens and among the aphid hosts with B. bassiana tending to kill aphids more rapidly. The mortality data were probit transformed, and a third-order polynomial model was fit to the data to describe responses of each host to conidial concentration and time after treatment. The potential for use of B. bassiana for aphid control is discussed.
TL;DR: The results of live-trapping winged aphids in an Ashby (1976) trap in potato crops in the Netherlands from 1983–1987 are reported, finding that 26 of them were able to transmit PVYN from potato to potato test plants.
Abstract: This paper reports the results of live-trapping winged aphids in an Ashby (1976) trap in potato crops in the Netherlands from 1983–1987. During this period, a total of 122 aphid species were trapped. Although only four of those species were able to colonise potato, 26 of them were able to transmit PVYN from potato to potato test plants. The transmission rates and relative efficiency factors (REF's) of those transmitters were determined.
TL;DR: Analysis of honeydew excreted by various sap-sucking insects indicated the presence of certain plant secondary constituents in the phloem of their host plants.
Abstract: Analysis of honeydew excreted by various sap-sucking insects indicated the presence of certain plant secondary constituents in the phloem of their host plants. Honeydew excreted by mealybugs (Pseudococcus longispinus), living onCastanospermum australe, contained the indolizidine alkaloid castanospermine, a potent β-glucosidase inhibitor. Similarly, honeydew from green peach aphids (Myzus persicae), feeding onSenecio vulgaris flower buds, contained the pyrrolizidine alkaloid senecionine, itsN-oxide, and hydrolytic products including retronecine. Cardenolides were detected in the honeydew of oleander aphids (Aphis nerii) feeding on oleander (Nerium oleander), indicating that these compounds are translocated in the phloem. On the other hand, honeydew from greenbugs (Schizaphis graminum), feeding on barley, lacked gramine or related indole metabolites. Similarly MBOA, the breakdown product of DIMBOA, was not detected in the honeydew of greenbugs living on DIMBOA-containing wheat.
TL;DR: ‘Suicidal’ behaviour was examined in pea aphids, Acyrthosiphon pisum, parasitized by Braconid wasps, Aphidius ervi, when reproductive potential varied and Coastal and interior aphid biotypes were cross-parasitized with wasps from non-local habitats.
TL;DR: In general aphid infestation of wheat seedlings slightly increased the concentration of all the hydroxamic acid derivatives, and aphids ingested hydroxamate acids and were able to detoxify some of the DIMBOA-aglucone they ingested.
Abstract: SUMMARY
The hydroxamic acids in the seedlings of four varieties of winter wheat were extracted initially in boiling methanol in order to avoid enzymatic hydrolysis. The increase in numbers of aphids on these varieties of wheat were recorded. HPLC analysis of hydroxamic acids in the extracts showed the presence of DIMBOA-glucoside, DIMBOA-aglucone and its benzoxazolinone (MBOA). There was a highly significant negative correlation between the concentration of DIMBOA-aglucone in the seedlings and aphid performance. However, the association between aphid performance and DIMBOA-aglucone in the tips of the seedlings was weaker. In general aphid infestation of wheat seedlings slightly increased the concentration of all the hydroxamic acid derivatives. Moreover, aphids ingested hydroxamic acids and were able to detoxify some of the DIMBOA-aglucone they ingested.
TL;DR: The hypothesis that melezitose, an aphid-synthesized sugar in honeydew causes an increase in the available soil nitrogen which improves tree assimilation thus benefitting the aphids was not supported.
Abstract: The effect of honeydew from an aphid (Pterocallis alni DeGeer) infesting a red alder (Alnus rubra Bong.) plantation in western Washington, USA, was studied experimentally. The purpose of the study was to examine the hypothesis that melezitose, an aphid-synthesized sugar in honeydew, causes an increase in the available soil nitrogen which improves tree assimilation thus benefitting the aphids. Aphids were removed from one plot by periodic spraying with Malathion and were left undisturbed on a control plot. The hypothesis was not supported by this study. Honeydew reaching the soil caused a reduction in available soil nitrogen, nitrogen mineralization rates, aboveground net primary production and nitrogen uptake by trees.
TL;DR: Results from this study provide information about the selectivity of pesticides for integration of biological and chemical controls for pecan aphids.
Abstract: The pecan aphid predators, Chrysoperla rufilabris (Burmeister) (egg, larva, and adult); adult Hippodamia convergens (Guerin-Meneville); Cycloneda sanguinea (L.); OUa v-nigrum (Say); and pupae of the parasite, Aphelinus perpauidus Gahan, were tested in the laboratory for mortality to registered commercial pesticides. Concentration-response lines were estimated for C. rufilabris larvae and adults. Only the half and full concentrations (recommended on label for pecan) were tested on the other species. Fungicides and acaricides caused 70% mortality to C. sanguinea . Phosalone, lindane, fiuvalinate, endosulfan, and azinphos-methyl were not toxic to A. perpallidus . Results from this study provide information about the selectivity of pesticides for integration of biological and chemical controls for pecan aphids.
TL;DR: Evidence was actually obtained that a small fraction of Tetraneura alates are passively transported and land on non-host plants, suggesting that the formation of a new host race proceeds parapatrically under disruptive selection and at a low level of gene flow.
Abstract: The process of host race formation in the aphid Tetraneura yezoensis is examined in relation to its population structure. T. yezoensis induces pouch galls on new leaves of Ulmus davidiana and U. laciniata. Its populations on the two host species are often sympatric. Fundatrices found on one elm species, when reciprocally transplanted to the other, suffered greatly reduced average fitness. This shows that aphid populations associated with the two elm species are genetically differentiated in physiological traits. Individual trees of each elm species showed large differences in susceptibility to gall formation and in bud burst time, and such between-tree variations were consistent over years. Overwintered eggs taken in early spring from four trees (two from each species) were incubated under the same temperature conditions. The average hatching time differed significantly even between populations from conspecific trees, and the sequence of egg hatching paralleled that of the leafing of those four trees. This between-tree difference in hatching time was consistent over years and was found to be genetic, showing that gene flow between aphid populations on separate trees is often restricted. The heterogeneity in host traits may have promoted the evolution of philopatry in this aphid. Of the fundatrices that hatched on a tree of one elm species, a few precent were preadapted to gall formation on the other elm species. This suggests that the formation of a new host race proceeds parapatrically under disruptive selection and at a low level of gene flow. Evidence was actually obtained that a small fraction of Tetraneura alates are passively transported and land on non-host plants.
TL;DR: Wheat growth stages from jointing to heading and a temperature regime of 18–21°C seem to be most suitable for rearing Russian wheat aphids in the laboratory, considering aphid fecundity and plant tolerance to insect and temperature stress.
Abstract: Plant growth stage and temperature exhibited a significant interaction ( P < 0.05) in their effects on reproductive life span, total life span, and production of nymphs per female of Russian wheat aphid, Diuraphis noxia (Mordvilko). Immature development and daily fecundity were not significantly affected by temperature and growth stage interactions. Minimum threshold temperature for immature development was estimated to be −1.57°C, and the number of degree-days to complete preimaginal development was 225.57. The intrinsic rate of increase (rm) was highest (0.255 ± 0.005) at 18–21°C during the jointing stage of wheat. At all other growth stages except tillering, rm also was highest at 18–21°C. Wheat growth stages from jointing to heading and a temperature regime of 18–21°C seem to be most suitable for rearing Russian wheat aphids in the laboratory, considering aphid fecundity and plant tolerance to insect and temperature stress.
TL;DR: Growth parameters of the trees were little affected by pollution alone, but were substantially reduced by either aphids or drought, and root weight was reduced by 24% more than expected from the additive effects of the combined SO(2) and drought treatment.
TL;DR: The behavior of Aphidius nigripes Ashmead was studied when searching for its host, the potato aphid Macrosiphum euphorbiae (Thomas), in the complex foraging environment of a mature potato plant to identify determinants of foraging behavior.
Abstract: The behavior of Aphidius nigripes Ashmead was studied when searching for its host, the potato aphid Macrosiphum euphorbiae (Thomas), in the complex foraging environment of a mature potato plant. The presence of hosts and host honeydew on the foliage was manipulated experimentally to identify determinants of foraging behavior. Parasitoid residence and searching times on a plant were longest with aphids present, but honeydew alone doubled the effect on these parameters compared with clean control plants. In the presence of honeydew, percentage of available leaves searched, time spent per leaf, and leaf surface area covered increased above control values. Parasitoids searched the lower leaf surface with greater intensity than the upper surface; the latter apparently was sampled solely for the presence of honeydew residues. On honeydew-contaminated plants, searching time was allocated preferentially to the upper half of plants where honeydew contamination was abundant, compared with a more evenly distributed search of clean plants. Parasitoids tended to follow horizontal sampling paths on the foliage of clean plants but horizontal and vertical search paths on honeydew-contaminated plants. These observations are discussed with reference to patch definition for aphid parasitoids and the potential for manipulation of aphid parasitoid behavior in pest control.
TL;DR: Host plant preference experiments were conducted with closely related taxa of the aphid genus Cryptomyzus, and presexual morphs (sexuparae and gynoparae) were used to determine the impact of host plant choice on reproductive isolation.
Abstract: . 1. Host plant preference experiments were conducted with closely related taxa of the aphid genus Cryptomyzus. Males, and presexual morphs (sexuparae and gynoparae), were used to determine the impact of host plant choice on reproductive isolation. In the case of host-alternating species these morphs are migratory and so will select the host plant.
2. Host plant preference of two closely related taxa of C. alboapicalis (Theobald) was found to promote their reproductive isolation. The preference of sexuparae of these monoecious taxa was more pronounced than that of the males.
3. Host plant preference and subsequent production of oviparae showed that C. galeopsidis (Kaltenbach) consists of two host races restricted to Ribes rubrum L. and R. nigrum L., respectively. The existence of clones, intermediate in their preference and reproductive performance on these plants, suggests that hybridization occurs.
TL;DR: Results suggest the existence of a synomonemediated interaction between the species involved, indicating potential avenues to enhance field parasitization rates through manipulation of the chemical environment of cole cropping systems.
Abstract: An interaction apparently mediated by synomones (Nordlundet al., 1981) betweenDiaeretiella rapae (M'Intosh), a primary parasitoid and the cabbage aphid,Brevicoryne brassicae (L.), was investigated under field conditions. Direct application of an allylisothiocyanate emulsion at a rate of 0.25 ml per broccoli plant consistently gave higher aphid parasitization rates and/or number of wasps per plant than those observed on plants treated with 0.25 ml of water or with 0.25 ml of wild mustard extract. These results suggest the existence of a synomonemediated interaction between the species involved, indicating potential avenues to enhance field parasitization rates through manipulation of the chemical environment of cole cropping systems.
TL;DR: The aphids, Cinara cupressi, Eulachnus rileyi Williams and Pineus pini, have invaded conifer plantations in southern and eastern Africa between 1968 and 1986, and are the first non-native pests to colonize these forest plantations.
Abstract: The aphids, Cinara cupressi (Buckton), Eulachnus rileyi Williams and Pineus pini (Macquart), have invaded conifer plantations in southern and eastern Africa between 1968 and 1986. Conifer plantations, and particularly pine plantations, are a new habitat in this region, having been established in the 1960s and 1970s. These aphids are the first non-native pests to colonize these forest plantations. As exotic pests, the aphids are suitable targets for classical biological control through the importation of natural enemies from Europe, the region of origin of the three aphids. The opportunities for biological control are explored and the prospects are encouraging. Details of the natural enemy complexes of the target pests in Europe are provided and discussed in relation to previous successful biological control programmes against conifer pests in other continents.
TL;DR: Observations on wasp distribution over time revealed that wasps spent less time on sprayed plants, relative to controls and, while on these plants, tended to concentrate activity on unsprayed surfaces.
Abstract: Foraging aphid parasitoids,Diaeretiella rapae M'Intosh, were exposed to sublethal doses of the insecticides pirimicarb, permethrin and malathion on brusslls sprouts plants. Observations on wasp distribution over time revealed that wasps spent less time on sprayed plants, relative to controls and, while on these plants, tended to concentrate activity on unsprayed surfaces. For permethrin and malathion, pesticide residues reversed the stereotypic upward foraging pattern of the wasp. Negative consequences of sublethal pesticide doses for parasitoid foraging efficiency are discussed.
TL;DR: In this paper, the authors investigated the effect of eating non-aphid food on the rate of antigen inactivation in three species of polyphagous predators, the carabids Bembidion lampros (Herbst), Nebria brevicollis (F) and the staphylinid Philonthus cognatus Stephens, by a quantitative enzyme-linked immunosorbent assay (ELISA).
Abstract: . 1. Disappearance of different amounts of aphid ingested by three species of polyphagous predators, the carabids Bembidion lampros (Herbst) and Nebria brevicollis (F.) and the staphylinid Philonthus cognatus Stephens, was monitored by a quantitative enzyme-linked immunosorbent assay (ELISA). The effect on the rate of inactivation of prey antigens by the ingestion of subsequent, non-aphid food was also studied.
2. Antigen inactivation was significantly more rapid in the staphyilinid than in the carabids.
3. No statistically significant differences were found in the rate of antigen inactivation between beetles which consumed only aphids and those which were given a different type of food after feeding on aphids; the detection period was longer in the former groups. A higher proportion of beetles with low levels of aphid antigen were found earlier in the latter group.
4. The results did not unequivocally support the prediction derived from optimal digestion theory that beetles without continuous access to food would retain an initial meal longer than beetles with unlimited access.