Showing papers on "Aphid published in 1989"

Aggregation in Aphis Varians: An Effective Strategy for Reducing Predation Risk

Abstract: It has been suggested that by clumping together, even defenseless prey may reduce their chances of being consumed by a predator. However, the advantage of clumping to prey may be negated by a strong aggregative response of predators to prey clusters. We studied the balance of forces that determine the advantage or disadvantage of clumping to prey in one particular case: the interaction between the aphid Aphis varians (Homoptera: Aphididae) and its predator Hippodamia convergens (Coleoptera:Coccinellidae). Aphid movement was congregative, i.e., aphids tended to stay within clumps of conspecifics. Furthermore, by quantifying the per capita population growth rates for aphid colonies of differing sizes, we found that individual aphids benefited by being clumped together. However, a predator—exclusion experiment indicated that clumping was beneficial to aphids only in the presence of predators. To gain a mechanistic understanding of why aphid congregation reduced predation risk to individuals, we examined the behavioral response of predators to aphid density. Predators exhibited a strong aggregating response: large colonies of aphids were attacked by more predators than were small colonies. In addition, ladybird feeding rate increased with increasing colony size. The total number of prey taken from colonies by predators, however, could not keep pace with the increase in aphid colony size, and thus the risk of predation to individual prey was "diluted" by prey numbers.

Factors determining the pest status of the bird cherry-oat aphid, Rhopalo-siphum padi (L.) (Hemiptera: Aphididae), in Europe: a study and review

Abstract: The biology and pest status of Rhopalosiphum padi (L.) in Europe are critically reviewed. New data are presented and the temporal occurrence of the aphid and its host-plants considered. In Britain, R. padi is a pest mainly because of its ability to transmit virus diseases, in particular barley yellow dwarf virus. In other European countries, especially in Scandinavia, R. padi is a pest in its own right. Predator and parasite complexes in Britain and Finland are compared and contrasted. The occurrence of R. padi as a pest of cereals in Europe is compared with that of Sitobion avenae (F.) and Metopolophium dirhodum (Walker). It is postulated that the great abundance of the primary host of R. padi, bird cherry (Prunus padus), and the spring planting of cereals in colder climates such as in Finland are major factors contributing to the differences in pest status of this aphid between Britain and in Scandinavia.

Spread and Control of Potato Leafroll Virus in Minnesota

Abstract: We compared importance of green peach aphid, Myzus persicae (Sulzer), and potato aphid, Macrosiphum euphormae (Thomas), apterae and alatae in secondary spread of potato leafroll virus (PLRV) and the control achieved with foliar sprays alone to that of conventional practice using a soil systemic. Density gradients of apterae were produced by application of insecticidal sprays. Spread of PLRV from centrally located infector units was monitored in foliage serologically. PLRV infection ranged from 23.7 to 74% in 1985 and 12.3 to 77.2% in 1986. PLRV infection was significantly correlated with cumulative green peach aphid and with potato aphid apterae-days both years. Green peach aphid was more abundant than potato aphid and alatae were few both years. At all distances (1-5 m) from infector units, infection across rows was 38.7-60.6% of that within rows. Steep gradients of PLRV infection with distance from infector units indicated short-distance movement of vectors and suggested that apterae were of prime importance in PLRV spread. Check plots without a PLRV source and not augmented with green peach apllid (1986 only) had a final PLRV incidence of 1.5%, indicating only minor invasion of these plots by viruliferous alatae. Weekly application of methamidophos sprays reduced PLRV incidence to that in plotstreated with aldicarb at planting and weekly methamidophos sprays. It should be feasible to develop a seed potato pest management program for Minnesota based on foliar sprays alone.

Intra- and interspecific competition for mutualists: ants as a limited and limiting resource for aphids.

Abstract: We present two years of experimental and descriptive data which support the hypothesis that fireweed aphids (Aphis varians) compete with intra-and interspecific aphid neighbors for the services of ant mutualists (Formica fusca and F. cinerea). Specifically, we have shown that ants are a Limited and Limiting resource for a tended aphid species. First, the presence of heavily aphid-infested fireweed shoots significantly reduced the number of ants tending neighboring conspecific populations on fireweed. Second, the presence of ant-tended aphids (Cinara sp.) on Engelmann spruce significantly reduced the number of ants tending neighboring aphid populations on fireweed. Third, the number of ants, and not just the presence of ants, had a significant effect on the fitness of fireweed aphids. Aphid populations tended by three or more F. cinerea exhibited significantly higher probabilities of persisting and growing through time than colonies tended by one or two ants. Aphid populations tended by F. fusca had a significantly higher probability of growing when tended by three or more ants only if they had declined in size during the previous week.

The role of experience in plant foraging by the aphid parasitoid Diaeretiella rapae (Hymenoptera: Aphidiidae)

Abstract: Experiments were conducted to test the hypothesis that plant learning by a relative plant-specialist parasitoid wasp should influence the probability of orienting to plant odors (plant finding) and the duration of searching on a plant after landing (plant examining). The insect tested was Diaeretiella rapaeM'Intosh (Hymenoptera: Aphidiidae), a parasitoid wasp that usually attacks aphids on cruciferous plants, but occasionally on other plants. Laboratory experiments using collard as the cruciferous plant and potato as the novel plant demonstrated that postemergence (adult) plant experience affected plant examining only on the less preferred plant, potato, and was reversible and relatively long-term (that is, lasted >2 days). Postemergence experience with potato did not increase orientation to potato odor in a wind tunnel, but postemergence experience with collard resulted in a trend of increased likelihood of flying to collard odor. Preemergence treatments affected plant finding but not plant examining.

Electrophoretic studies on agricultural pests.

Abstract: Electrophoresis in agricultural pest research - a technique of evolutionary biology, M.F.Claridge electrophoretic studies - perspectives for population biology, R.J.Berry genetic studies of species differences and their relevance to the problem of species formation in "Drosophila", R.S.Singh the complexities of host races and some suggestion for their identification by enzyme electrophoresis, S.H.Berlocher population genetics studies of fruit flies of economic importance, especially medfly and olive fruit fly, using electrophoretic methods, M.Loukas host-associated differentiation in armyworms (Lepidoptera, Noctuidae) - an allozymic and mitochondrial DNA perspective, D.P.Pashley the use of electrophoretic data in a study of gene flow in the pest species "Heliothis armigera" (Hubner) and "H. punctigera" Wallengren (Lepidoptera, Noctuidae), J.C.Daly estimation of genetic variability amongst Coleoptera, T.H.Hsiao electrophoretic studies on geographic populations, host races, and sibling species in insect pests, S.B.J.Menken study of variation of aphid populations using enzymes and other traits, K.Wohrmann and J.Tomiuk use of genetic markers (allozymes) to study the structure, overwintering, and dynamics of pest aphid populations, H.D.Loxdale and C.P.Brookes enzyme differences within species-groups containing pest aphids, R.L.Blackman et al electrophoretic studies on plant hoppers and leaf hoppers (Homoptera) of agricultural importance, J.Den Hollander speciation by hybridization in insects, L.Bullini and G.Nascetti electrophoretic variation in post-harvest agricultural pests, and its implications, D.Wool the role of electrophoresis in the biochemical detection of insecticide resistance, A.L.Devonshire genetic fingerprinting of house sparrows, "Passer domesticus", J.H.Wetton and D.T.Parkin the population structure of "Deroceras reticulatum" (Mollusca, Pulmonata, Limacidae), C.C.Fleming characterization of populations of pathotypes of potato cyst nematodes, J.Bakker and F.J.Gommers isoelectric focusing techniques for the identification of plant-parasitic nematodes, M.P.Robinson the use of electrophoresis in the study of Hymenopteran parasitoids of agricultural pests, W.Powell and M.P.Walton the use of electrophoresis for determining patterns of predation in arthropods, R.A.Murray et al.

Transmission of potato virus Y by aphids trapped in potato crops in southern England.

Abstract: Harrington et al. (1986) assessed the relative efficiency with which different aphid species transmitted potato virus Y (PVY), by trapping flying aphids on a net downwind of a plot of infected potatoes and transferring the aphids to tobacco seedlings. This paper reports the extension of that work over further seasons and identifies three more vector species,Aphis sambuci, Myzus cerasi andDysaphis sp. A method for determining the proportion of those aphids caught on the net that had landed and probed in the crop is suggested. The use of such information to improve a model of virus spread is discussed.

Parasitoid Response to Concentration of Herbivore Food Plants: Finding and Leaving Plants

Abstract: We hypothesized that a parasitoid of an herbivore would be attracted to large rather than small patches of plants that provide food for the herbivore. We conducted experiments to determine whether such parasitoids would be more likely to find and/or less likely to leave large patches of their victims' host plants. We also examined whether prey density (independent of patch size) affects plant finding or leaving. These aspects of plant foraging behavior were examined for Diaeretiella rapae (Hymenoptera: Aphidiidae), a parasitoid wasp that attacks aphids primarily on cruciferous plants. Arrival rates of naturally occurring D. rapae in artificial patches of 5, 10, 20, and 40 potted collard plants were measured in a field experiment. There was no patch-size effect (plants in larger patches were not more likely to be found), and plants with aphids were not more likely to be found than aphid-free plants. Furthermore, there was no dosage response to water bowl traps baited with chemical plant attractant placed in the same field. Leaving rates were measured in a greenhouse experiment using dispersal cages containing 1, 4, or 16 plants and 0, 10, or 100 aphids. Leaving rate decreased in larger patches independently of aphid density, which also affected leaving rate. We conclude that plant leaving may be equally or more important than plant finding in determining abundance of D. rapae in patches of crucifers. The significance of this result is discussed.

Effects of Russian wheat aphid infestation on barley plant response to drought stress

Abstract: The influence of Russian wheat aphid (Diuraphis noxia Mordvilko) infestation on the response of barley (Hordeum vulgare L. ev Hazen) plants to drought stress was investigated. Fourteen-day-old plants were infested with eight apterous adult aphids, which were removed 7 days later with systemic insecticide. Leaves previously infested with aphids had lower relative water content, reduced stomatal conductance, more negative water potential, lower levels of chlorophyll and higher levels of amino-N, proline and glycinebetaine than corresponding leaves from uninfested plants. When water was withheld for a period of 7 days after aphids were removed, the relative water content of previously infested plants dropped steadily from 0.89 to 0.60, while the relative water content of uninfested plants remained at about 0.94 for the first 4 days of the drought stress period followed by a steady drop to about 0.77 by the end of the drought stress period. Leaf water potentials dropped steadily during the drought stress period in both previously infested (-1.14 to -1.91 MPa) and unin-fested (-0.54 to -1.52 MPa) plants. Analysis of glycinebetaine and proline levels at the end of the drought stress period indicated that leaves of previously infested plants accumulated lower levels of these solutes than leaves from uninfested plants. Upon alleviation of drought stress, plants previously infested with aphids showed little increase in dry weight while younger leaves and tillers from uninfested plants showed large increases. It is concluded that Russian wheat aphids cause drought-stress symptoms in leaves of infested plants even in the presence of ample root moisture. The observations of low levels of glycinebetaine and proline present in leaves after water was withheld from roots and lack of leaf growth upon alleviation of drought stress in previously-infested plants, suggest that aphid infestation limits the capacity of barley plants to adjust successfully to drought stress.

Inheritance of potato aphid resistance in hybrids between Lycopersicon esculentum and L. pennellii.

Abstract: The potato aphid, Macrosiphum euphorbiae Thomas, is an important pest of tomato, Lycopersicon esculentum Mill., because it transmits tomato viruses and directly reduces crop yields by its feeding. This study was conducted to determine whether the wild tomato species, Lycopersicon pennellii (Corr.) D'Arcy, would be useful as a source of potato aphid resistance for tomato. Type IV trichome density and aphid resistance were assessed in six generations (P1, P2, F1, F2, BC1P1, and BC1P2) from crosses between L. pennellii (LA 716) and two tomato cultivars, New Yorker and VF Vendor. Weighted leastsquares were used in joint scaling tests to estimate the relative importance of gene effects on type IV trichome density and potato aphid resistance of the hybrids. A simple additive-dominance model adequately explained the variation in type IV trichome density. Models which included digenic epistatic effects were required to explain the variation in aphid resistance. Standard unit heritability estimates of aphid resistance in the backcross to L. esculentum were obtained by regression of BC1F2 off-spring families on BC1F1 parents. Regression coefficients and heritability estimates varied between years with the level and uniformity of the aphid infestation. In the 1985-1986 growing seasons, when aphid infestations were uniform, aphid resistance exhibited a moderate level of heritability (29.8% ± 14.1% and 47.1% ± 11.5% in New Yorker and VF Vendor backcross populations, respectively). The non-uniform aphid infestation of 1984 resulted in lower heritability estimates in the 1984-1985 growing seasons (16.1% ± 15.7% and 21.9% ± 14.8% in the New Yorker and VF Vendor backcross populations, respectively). Selection for potato aphid resistance would probably be most efficient if it were delayed until gene combinations are fixed in later generations, because of the large epistatic effects and the low heritability of this trait in seasons with variable aphid infestations.

Host plant iridoid-based chemical defense of an aphid, Acyrthosiphon nipponicus , against ladybird beetles

Abstract: A Rubiaceae-feeding aphid,Acyrthosiphon nipponicus, is seldom attacked by the ladybird beetle,Harmonia axyridis. A potent deterrent against the beetle was isolated from the aphid and identified as paederoside, an iridoid glycoside originating in the aphid's host,Paederia scandens. The iridoid content was as high as 2% of the intact body weight, and a large portion was found in the cornicle secretion.

Use of insect antifeedants against aphid vectors of plant virus disease

Abstract: The probing and feeding behaviour of aphids can result in uptake of viruses from infected plants and subsequent transmission to healthy plants. It is possible to interfere with virus acquisition and transmission by influencing aphid host-selection and feeding behaviour with antifeedant chemicals. Published work is reviewed and new work is presented in this paper. The two most successful classes of antifeedants against aphids are (a) compounds derived from the aphid alarm pheromone and (b) plant-derived antifeedants such as the sesquiterpene (-)-polygodial. Results with these and other compounds are discussed in terms of antifeedant activity against Myzus persicae, their effects on resistant aphids and the evidence for decŕease in virus spread by aphids in laboratory and field.

Disruption of web structure and predatory behavior of a spider by plant-derived chemical defenses of an aposematic aphid

Abstract: Two toxic and bitter-tasting cardenolides (cardiac-active steroids) were sequestered by the brightly colored oleander aphid,Aphis nerii B. de F., from the neotropical milkweed host plantAsclepias curassavica L. After feeding on milkweed-reared aphids, the orb-web spiderZygiella x-notata (Clerck) built severely disrupted webs and attacked fewer nontoxic, control aphids, whereas the webs of spiders fed only nontoxic aphids remained intact. The regularity and size of the prey-trapping area of webs were reduced significantly in proportion to the amount of toxic aphids eaten. The effects of toxic aphids on spider web structure were mimicked by feeding spiders the bitter-tasting cardenolide digitoxin, a cardenolide with similar steroidal structure and pharmacological activity to the two aphid cardenolides. These results show that the well-known effects of psychoactive drugs on spider web structure are more than interesting behavioral assays of drag activity. Similar effects, produced by plant-derived chemicals in the spider's aphid prey, are relevant to the ecology and evolution of interactions between prey defense and predator foraging.

Comparison of sources of resistance to leaf aphids in lettuce (Lactuca sativa L.)

Abstract: Three lines of lettuce with resistance to Nasonovia ribisnigri, based on the dominant Nr-gene, and four lines selected for partial resistance to Myzus persicae were tested against three species of leaf aphid: N. ribisnigri, M. persicae and Macrosiphum euphorbiae. The effect of the Nr-gene was also studied in a segregating F2 population.

Release of chrysoperla carnea stephens (neuroptera: chrysopidae) for control of the green apple aphid, aphis pomi degeer (homoptera: aphididae)

Abstract: Release of the chrysopid, Chrysoperla cornea Stephens, at a rate of ca. 335 000 eggs per hectare, reduced significantly the numbers of apterous adults and nymphs of the green apple aphid, Aphis pomi DeGeer, on dwarf apple trees. Greater reduction in aphid numbers occurred in 1984 than in 1985, and the efficiency of the predator might have been influenced by the predator:prey ratios (1:10 and 1:19) used and by the mean daily temperature that occurred during the test periods. Application of azinphosmethyl (Guthion 50% wp, 0.105 and 0.075 kg AI/100 L) did not adversely affect predation of apterous A. pomi by larvae of C. carnea.

The effect of augmenting grain aphid (Sitobion avenae) numbers in a field of winter wheat in spring on the aphid's abundance in summer and its relevance to the forecasting of outbreaks

Abstract: Summary Sitobion avenae was introduced into areas within a field of winter wheat in Norfolk in mid-May 1985, when the indigenous population was negligible. Aphid numbers in these areas increased for the first 3 wk and declined for the next 4. A second S. avenue introduction into the same areas and into previously uninfested areas was carried out 5 wk after the first introduction, when the crop was at ear emergence complete (G.S. 59). This increased aphid numbers in the previously uninfested areas, but numbers in the previously infested areas continued to decline to below the level in control areas during the subsequent 2 wk. Populations in all areas then increased rapidly to a maximum, followed by a rapid final decline. Monitoring of the aphid and natural enemy populations, and caging aphids onto the crop, revealed that the principal cause of the population decline around G.S. 59 was predation by syrphids. The relevance of these findings to the problem of forecasting S. avenae outbreaks is discussed, and a general explanation for cereal aphid outbreaks is put forward.

Impact of the imported fire ant on laboratory populations of cotton aphid (aphis gossypii) predators

Abstract: The presence of a few red imported fire ants, Solenopsis invicta Buren, workers on aphid bearing cotton plants reduced aphid predator effectiveness in the laboratory. The predators Hippodamia convergens Guerin-Meneville adults and 3rd instar larvae were effective in reducing Aphis gossypii Glover populations as did 3rd instar larval Chrysopa carnea Stephens, Scymnus louisianae Chapin and Syrphus sp. larvae. However, all of these predators were ineffective in the presence of fire ants which were capable of killing all species although both Scymnus and Syrphus larvae sometimes escaped. Although predators may be killed they may prefer areas of low ant encounters in the field thus surviving and reducing their impact on fire ant tended aphid populations.

Comparison of sweep net, D-vac, and absolute sampling, and diel variation of sweep net sampling estimates in lentils for pea aphid (Homoptera: Aphididae), nabids (Hemiptera: Nabidae), lady beetles (Coleoptera: Coccinellidae), and lacewings (Neuroptera: Chrysopidae)

Abstract: Relative accuracy of sweep net sampling was compared with D-vac (D-vac, Riverside, Calif.) and absolute sampling methods for determining population densities of pea aphid, Acyrthosiphon pisum (Harris), Nabi. s spp., Hippodamia spp., and Chrysopa spp. in lentils ( Lens culinaris Medikus). Relative effects of the a biotic environment, predators, and time of sampling on population estimates also were determined during 2 yr. Original counts, area, and volume adjustments were used to evaluate accuracy of the sampling method. Volume adjustment was most accurate and was used in all subsequent evaluations. Sweep net estimates of pea aphid, Nabis spp., and Hippodamia spp. densities were similar to those obtained with absolute and D-vac sampling methods, although sweep net sampling consistently gave lower population estimates than those found for absolute sampling. In these experiments, the sweep net did not adequately sample the Chrysopa spp. in lentils. The time of sampling was significant when sampling for pea aphid; however, it was not as important for sampling of the three insect predators. Each year, sweep net samples were taken randomly at two locations in two fields every hour for 72 consecutive hours. The a biotic factors studied were light intensity, temperature, relative humidity, and wind velocity; Nabis spp., Hippodamia spp., and Chrysopa spp. were the predator groups studied. Light intensity was the only a biotic factor that was significantly correlated with pea aphid numbers over both years, whereas all four a biotic factors had significant correlations at low aphid densities in 1983. The diurnal sine of hour was significantly and positively correlated with number of aphids collected by sweep net each hour, whereas predator densities were significantly and negatively correlated with aphid densities over both years. Optimum sampling time for pea aphids in lentils can depend on the dominant predator group being sampled; however, for pea aphids and all predator groups, a sample taken in late morning is preferable when sweep net samples are taken.

Geographic and clonal variation in the milkweed- oleander aphid, Aphis nerii (Homoptera: Aphididae), for winged morph production, life history, and morphology in relation to host plant permanence

Abstract: Populations of the milkweed-oleander aphid,Aphis nerii, were sampled in California, Iowa and Puerto Rico. Among these localities the aphid's host plants differ greatly in permanence. I compared populations for migratory potential, measured as the proportion of winged offspring produced in response to being crowded, and for life history and morphometric traits of the subsequent adult winged aphids. I predicted a negative correlation between degree of host plant permanence and migratory potential. As predicted, aphids from Iowa, where migration on to temporary hosts must occur each year, produce a greater proportion of winged offspring (37.7%) than those from California (25.7%) or Puerto Rico (31.6%) where hosts are more permanent. However, hosts in Puerto Rico appear to be more permanent than those in California, yet the difference between populations for migratory potential was opposite to that predicted. Within California the prediction again held: aphids collected from the most impermanent sites produce the greatest proportion of winged offspring. There were no population differences for any life history or morphometric traits of winged aphids that are important contributors to fitness or migratory ability such as time to reproductive maturity, fecundity or wing length. Nor did any traits covary with migratory potential. Thus, there does not appear to be an association of life history and morphology with migratory potential that could enhance the colonizing ability of migrant aphids. I was unable to detect population differentiation for life history and morphology even though there is ample genetic variation within populations on which selection could act and an absence of constraints arising from genetic correlations that could prevent appropriate evolution of traits within populations. The exploitation of temporary host plants therefore occurs by an increase in the number of colonists produced and not by change in life history or morphology of those colonists.

Influence of Temperature on Reproduction, Development, and Intrinsic Rate of Increase of Russian Wheat Aphid, Greenbug, and Bird Cherry-Oat Aphid (Homoptera: Aphididae)

Abstract: The effects of constant (1O°C) and fluctuating (5-15°C and I-19°C) temperature regimes on the reproduction, development, and intrinsic rate of increase of the Russian wheat aphid, Diuraphis noxia (Mordvilko), greenbug, Schizaphis graminum Rondani, and the bird cherry-oat aphid, Rhopalosiphum padi Fitch, were studied in the laboratory at an average-temperature regime (1O°C) that is common in the spring when all three of these aphids are found in small grain fields in the Texas Panhandle. Significant differences in nymphal development and total lifespan were observed among species within a temperature regime and among temperature regimes for a species. Natality was highest for D. noxia and R. padi at 5-15°C; S. graminum natality was highest at I-19°C. Estimates of the intrinsic rate of increase (rm,) for the three aphid species were highest at I-19°C (0.188 for D. noxia , 0.144 for S. graminum , and 0.200 and for R. padi) .

The effects of temperature and host quality on the rate of increase of the grain aphid (Sitobion avenae) on wheat

Abstract: Summary From 10°C to 25°C Sitobion avenae reared on wheat developed faster, had a higher mean relative growth rate and a higher intrinsic rate of increase on ears than on the flag leaves. At temperatures above 25°C there is a marked decline in the performance of the aphid. The intrinsic rate of increase is strongly correlated with the mean relative growth rate during development for both aphids reared on ears and flag leaves from 10°C to 25°C.

Biology ofAllothrombium pulvinum (Acariformes: Trombidiidae), a potential biological control agent of aphids in China

Abstract: Allothrombium pulvinum Ewing is a common natural enemy of aphids and other small arthropods in China. It is univoltine species. The eggs hatch in spring, nymphs emerge in early summer, and adults emerge in autumn. Larvae are ectoparasites of aphids, whereas deutonymphs and adults are free-living predators of aphids, spider mites and some lepidopterous eggs. Adults hibernate in soil during winter and females lay their eggs in spring. In the laboratory the duration of immature stages is 74 days at 20–30°C. Larvae kill their host within 1–3 days when the mite load of the host is 2 or more. They decrease the reproductive rate of adult aphids and arrest the development of early-instar aphid nymphs when the mite load is 1. Larvae are capable of controlling the host population growth when the level of parasitism is high. Owing to its wide occurrence,A. pulvinum could be a potential candidate in the biological control of aphids. It is suggested that its impact on the host pest be evaluated in IPM programs in the future.

Interactions between plant and aphid genotypes in resistance of lettuce to Myzus persicae and Macrosiphum euphorbiae

Abstract: Six lettuce lines, representing two types of resistance to the green peach aphid, Myzus persicae, and a control line with high susceptibility to M. persicae were tested for resistance to six different clones of Myzus persicae and two clones of the potato aphid, Macrosiphum euphorbiae.

Effect of honeydew and hosts on plant colonization by the aphid parasitoidEphedrus cerasicola

Abstract: Females ofEphedrus cerasicola Starý were released into small glasshouses (13.6 m3) or cages (0.125 m3) which contained paprika plants in 2 of the following categories: fresh plants (without honeydew and aphids), honeydew-contaminated plants (aphids removed) and aphid-infested plants (with honeydew). Two hundred females were released into each glasshouse with 20 plants, 10 of each category, while 10 females were released into the cages with 2 plants, one of each category. Control experiments with only fresh plants were conducted in both the glasshouses and the cages. The female parasitoids on each plant were counted at regular intervals for 24 or 48 h in the glasshouse and for 4 h in the cage experiments; this number was used as an indicator of plant preferences. The following preferences were established (preferred plant > less preferred plant): honeydew-plant > fresh plant, aphid-plant > fresh plant, aphid-plant > honeydew-plant. The number of females on the aphid-plants increased throughout the experimental period, whereas the number on the honeydew-plants tended to be more stable.

Release and establishment of Aphidius spp. (Hymenoptera: Aphidiidae), parasitoids of pea aphid and blue green aphid in New Zealand

Abstract: Three Aphidius spp. parasitoids of the lucerne aphids, pea aphid (P A) and blue green aphid (BGA), were introduced into New Zealand from 1977 to 1982. A. eadyi spread rapidly and now occurs in all the main lucerne-growing areas. In comparison, A. ervi was difficult to establish, failing to persist after several initial recoveries, but was eventually established from releases of se:parate strains in the North and South Islands, replacing A. eadyi as the predominant parasitoid in the North Island. Despite large releases, A. smithi has not established. A. ervi shows a preference in the field for BGA, but in the laboratory it demonstrated the ability to adapt from PA to BGA in two generations. Laboratory experiments showed that A. eadyi has a higher fecundity and faster development rate than A. ervi indicating that it competes better for PA. However, the polyphagy of A. ervi may be significant in its increasing predominance in the field. Comparisons are drawn with North American results.