Aphelinus Asychis Research Articles

Effects of photoperiod and temperature on adult oligopause of Aphelinus asychis and larval diapause of A. albipodus (Hymenoptera: Aphelinidae)

The effects of photoperiod and temperature on the dormancy of two aphid parasitoids in Japan, Aphelinus asychis and A. albipodus, were studied in the laboratory. Adult (reproductive) dormancy was induced in A. asychis under 10L : 14D at moderate temperatures and under 15L : 9D at low temperatures. Dormant adults started oviposition 6–17 d after emergence under 10L : 14D at 15 and 18°C. Transferring newly emerged adults from 10L : 14D at 15 and 18°C to 15L : 9D at 20°C caused an apparent reversal of dormancy induction within 1–2 d. It was believed that adult dormancy in A. asychis conforms to “oligopause” rather than “diapause” sensu Mansingh (1971). Adults of A. asychis showed an apparent variation in abdominal coloration from yellowish brown to black. The proportion of females with dark abdominal coloration was higher under 10L : 14D than under 15L : 9D and high at lower temperatures. We regarded this polyphenism as a part of the “diapause syndrome” because oligopause and abdominal coloration were controlled by the same environmental factors. Aphelinus albipodus entered diapause as last instar larvae. The critical photoperiod for diapause induction was 11–12 h at 18°C, and diapause was terminated within six weeks by cold treatment (10L : 14D, 5°C).

Complementary biocontrol of aphids by the ladybird beetle Harmonia axyridis and the parasitoid Aphelinus asychis on greenhouse roses

We investigated whether two biocontrol agents, the parasitoid wasp Aphelinus asychis Walker and the predatory ladybird beetle Harmonia axyridis Pallas, would act in concert to reduce densities of an aphid ( Macrosiphum euphorbiae Thomas) that attacks greenhouse-grown roses ( Rosa hybrida L.). We conducted three types of experiments: feeding trials in microcosms that examine predator preference for mummies versus aphids; a longer-term pairing of the two natural enemies and aphids on whole plants in large cages; and a trial release of ladybird beetles into a rose greenhouse infested with the aphid and parasitoid. In the microcosm feeding trials both larvae and adults of H. axyridis fed on aphids, but also on parasitoid mummies, raising the possibility that intraguild predation of parasitoids by H. axyridis could disrupt aphid control. In cages, ladybird beetles dampened peak aphid densities during an outbreak without altering densities of parasitoid pupae or the ratio of parasitoids to aphids. In our whole-greenhouse release, we saw no evidence that H. axyridis disrupted aphid control by resident A. asychis . Together, these results suggest that H. axyridis can complement aphid biocontrol by the parasitoid A. asychis , rather than disrupting control through intraguild predation.

Supercooling capacity of Eurasian and North American populations of parasitoids of the Russian wheat aphid, Diuraphis noxia

Supercooling points were estimated for seven populations of >Aphelinus albipodus, five populations of >Aphelinus asychis, and four populations of >Diaeretiella rapae to assess whether their supercooling points were sufficiently low to provide the potential for overwintering survival in colder temperate climatic areas. Test individuals from all 16 of the parasitoid populations were collected originally from mummies of the Russian wheat aphid, >Diuraphis noxia. Mummies containing parasitoid pupae were maintained for 1 wk under three different temperature conditions (treatments): at room temperature (24.8 ± 0.2 °C), 1 wk at 0 °C, and 1 wk −5 °C, and the supercooling points across treatments, and within and among species were compared. Statistical differences in supercooling points were found among populations of >A. albipodus for each treatment, and for >A. asychis when maintained for 1 wk at room temperature. No differences in supercooling points were found among populations of >D. rapae mummies maintained under the three temperature treatments. The lowest supercooling points obtained for the three parasitoid species maintained at room temperature were the >A. albipodus population from Montana (−31.68 °C), the >A. asychis population from Greece (−32.04 °C), and the >D. rapaepopulation from the Caucasus (−33.12 °C). Preconditioning the parasitoid mummies to cold had no effect on the supercooling points for >A. albipodus, and in some cases unexpectedly increased the supercooling points for >A. asychisand >D. rapae. In comparing the overall mean supercooling points of the three parasitoid species, no differences were found within species (among temperature treatments), nor among species (within temperature treatments). It was concluded that observed differences in supercooling points of only a few degrees Centigrade among parasitoid populations and species would not be expected to cause differences in their overwintering success, especially given the expected variability in temperatures within and among overwintering sites.

Molecular Evidence for a Species Complex in the Genus <I>Aphelinus</I> (Hymenoptera: Aphelinidae), with Additional Data on Aphidiine Phylogeny (Hymenoptera: Braconidae)

Mitochondrial 16s rDNA was sequenced from nine different populations of Aphelinidae and 10 of aphidiinae. Sequence divergences between populations within a species are low, ranging from 0 to 0.38%. Divergences among species within the same genus range from 0 to 8.71%. Aphelinus asychis Walker has a sequence divergence from the other Aphelinus spp. of 8.71%, which is even higher than the divergences among the aphidiine genera Lysiphlebus, Aphidius and Diaeretiella. Our 16s rDNA phylogeny for aphidiines is concordant with a previously published NADH1 dehydrogenase phylogeny. Our analysis identifies a complex comprising A. albipodus (Hayat & Fatima), A. varipes (Foerster), and A. hordei (Kurdjumov). The sequence divergences within this complex are low, ranging from 0 to 0.38% with an average of 0.19%, which suggests that the three species within the A. varipes complex diverged within the last ≈90,000 yr.

Interactions among the Entomopathogenic Fungus, Paecilomyces fumosoroseus (Deuteromycotina: Hyphomycetes), the Parasitoid, Aphelinus asychis (Hymenoptera: Aphelinidae), and Their Aphid Host

Abstract The interactions among the hyphomycete, Paecilomyces fumosoroseus, the Russian wheat aphid, Diuraphis noxia, and its common parasitoid, Aphelinus asychis, were investigated under laboratory conditions to determine if fungal infection of the aphid host had an effect on oviposition and feeding behavior of the female parasitoid and on development of parasitoid progeny. Aphids were first treated with 2 times the LD 95 of P. fumosoroseus for D. noxia third instars (5.2 × 10 4 conidia/cm 2 ). At various intervals afterward they were exposed to 4- to 5-day-old mated parasitoid females for 1 h. Various combinations of treatments were examined: exposure to P. fumosoroseus and parasitization simultaneously; exposure to parasitoids 24–96 h after treatment with fungus; exposure to the parasitoid alone; and fungal treatment alone. The average number of aphids probed by the parasitoids was not significantly influenced by host infection with P. fumosoroseus, but duration of ovipositor insertion was influenced by the length of the time interval between exposure to P. fumosoroseus and subsequent exposure to the parasitoid. Parasitoid females spent considerably less time with their ovipositor inserted in dead aphids and in aphids that had been exposed to P. fumosoroseus 72 h prior to contact with the parasitoids. The number of dead aphids fed upon by parasitoids was significantly less than in the other treatment groups. The percentage of successfully parasitized D. noxia was significantly reduced as a function of the time between treatment with P. fumosoroseus and parasitoid oviposition. The effect of previous parasitization on the ability of the fungus to infect aphids and interfere with parasitoid development within host aphids was also investigated. The number of mummies produced by two female A. asychis during 24 h of exposure varied from 20.3 to 23.0 and was not significantly different when the aphids were first exposed to the parasitoids and then treated with P. fumosoroseus 24, 48, 72, and 96 h after exposure. No difference in time between oviposition and emergence of the F1 generation of the parasitoid for groups treated with the fungus and the untreated groups was noted, but the percentage of emergence of the F1 generation of A. asychis was significantly lower among the aphids exposed to the parasitoid and treated with the fungus 24 h afterward than for the untreated aphids. Various findings of this study demonstrate the potential of synergistic interaction of P. fumosoroseus and A. asychis for the biological control of D. noxia.

Abundance and Effects of Predators and Parasitoids on the Russian Wheat Aphid (Homoptera: Aphididae) Under Organic Farming Conditions in Colorado

Diuraphis noxia (Mordvilko) is an exotic, economically important pest in North American cereal crops. A survey of insect natural enemies of D. noxia was made from 1991 to 1994 on a farm using organic farming methods. Crested wheatgrass, Agropyron cristatum L., had fewer D. noxia and natural enemies than barley, Hordeum vulgare L., or wheat, Triticum aestivum L., but on all plants D. noxia was the most abundant aphid. We observed 41 species of natural enemies: 15 carabids, 12 coccinellids, six spiders, five syrphids, two nabids, and two chrysopids. The most consistently abundant were the coccinellids and nabids. Hippodamia convergens (Guerin) and Nabis alternatus Parsh were the most common species in each family, respectively. Diaeretiella rapae M’Intosh was the only primary parasitoid found in the 4-yr study, and D. noxia parasitism rates were generally <5%. Four hyperparasitoids, found in association with D. rapae, combined to make a 29% average hyperparasitism rate. Predator and parasitoid exclusion studies using cages showed aphid populations to be between 2.6 and 11.2 times higher in cages compared with wheat plants exposed to natural enemies. Four predatory species were released—Eupeodes nuda (F.), Hippodamia variegata (Goeze), Leucopis ninae Tanasijtshuk, and Propylea quatuordecimpunctata (L.). Of these, only a small colony of eight L. ninae and only one P. quatuordecimpunctata were later observed. Four parasitoids species were released—Aphelinus asychis Walker, Aphelinus varipes Forester, Aphelinus matricariae Haliday, and Diaerietilla rapae. Only A. asychis and D. rapae were observed after the release date, although D. rapae were already present.

Abundance and Effects of Predators and Parasitoids on the Russian Wheat Aphid (Homoptera: Aphididae) Under Organic Farming Conditions in Colorado

Diuraphis noxia (Mordvilko) is an exotic, economically important pest in North American cereal crops. A survey of insect natural enemies of D. noxia was made from 1991 to 1994 on a farm using organic farming methods. Crested wheatgrass, Agropyron cristatum L., had fewer D. noxia and natural enemies than barley, Hordeum vulgare L., or wheat, Triticum aestivum L., but on all plants D. noxia was the most abundant aphid. We observed 41 species of natural enemies: 15 carabids, 12 coccinellids, six spiders, five syrphids, two nabids, and two chrysopids. The most consistently abundant were the coccinellids and nabids. Hippodamia convergens (Guerin) and Nabis alternatus Parsh were the most common species in each family, respectively. Diaeretiella rapae M'Intosh was the only primary parasitoid found in the 4-yr study, and D. noxia parasitism rates were generally ,5%. Four hyperparasitoids, found in association with D. rapae, combined to make a 29% average hyperparasitism rate. Predator and parasitoid exclusion studies using cages showed aphid populations to be between 2.6 and 11.2 times higher in cages compared with wheat plants exposed to natural enemies. Four predatory species were released—Eupeodes nuda (F.), Hippodamia var- iegata (Goeze), Leucopis ninae Tanasijtshuk, and Propylea quatuordecimpunctata (L.). Of these, only a small colony of eight L. ninae and only one P. quatuordecimpunctata were later observed. Four parasitoids species were released—Aphelinus asychis Walker, Aphelinus varipes Forester, Aphelinus matricariae Haliday, and Diaerietilla rapae. Only A. asychis and D. rapae were observed after the release date, although D. rapae were already present.

Predatory and parasitic activity of Aphelinus asychis (Hymenoptera: Aphelinidae) following exposure to the entomopathogenic fungus Paecilomyces fumosoroseus (Deuteromycotina: Hyphomycetes) under different humidity regimes

The effect of the hyphomycete Paecilomyces fumosoroseus (Wise) Brown &amp; Smith on the predatory and parasitic activity of Aphelinus asychis Walker, a common parasitoid of the Russian wheat aphid, Diuraphis noxia (Mordvilko), was investigated under three different humidities. Three cohorts of 20 female A. asychis were treated with 5.2 x 10(4) spores/cm² (twice the LD95 for D. noxia). Each female was then individually maintained in a ventilated Petri dish in which were placed three barley leaves and 20 third-instar D. noxia. Cohorts of 20 treated females were each held at one of the following relative humidities along with an equal number of untreated control insects: 67-73%, 85-89%, and 94-98%. Every 24 hours over a period of one week, the surviving parasitoids were transferred into a new Petri dish provided with fresh leaves and 20 aphids. After each 24-hour period of exposure and for each parasitoid, dead aphids were counted and the leaves with live aphids were transferred to barley plants to permit the re-establishment of the aphids. Nine days after the transfer of aphids, the mummies were counted. The total number of aphids consumed and mummies originated from the treated parasitoids incubated at 94-98% RH was significantly lower than in the control group. There was a significant decline in predation and parasitism per treated female per day and a progressive reduction in the number of treated parasitoids surviving each day. The death of all treated parasitoids incubated for 7 days at 94-98% RH after treatment and the high level of mycosis in cadavers demonstrate the susceptibility of adult A. asychis to P. fumosoroseus at high relative humidity. However, the reduced suceptibility of parasitoids at lower humidities means that may still be possible to construct an integrated program of pest management using parasitoids and pathogens.

Oviposition Behavior ofAphelinus asychis(Hymenoptera: Aphelinidae) andAphidius matricariae(Hymenoptera: Aphidiidae) and Defense Behavior of Their HostDiuraphis noxia(Homoptera: Aphididae)

Laboratory experiments were done to determine whether differences in attack behavior of Aphelinus asychis Walker and Aphidius matricariae Haliday and defense by their host Diuraphis noxia (Mordvilko) could explain higher parasitism by A. asychis in the field. Attack behavior differed strongly between the 2 parasitoid species: A. asychis took 4 times longer to oviposit in individual hosts than A. matricariae, and A. matricariae parasitized 6 times more hosts per unit time. These differences may have arisen in part because A. asychis appears to assess host quality with its ovipositor after insertion and A. matricariae appears to assess host quality by antennal palpation before ovipositor insertion. Although adult A. asychis uses some hosts for nutrition rather than oviposition and A. matricariae does not, A. matricariae still killed more hosts per unit time than A. asychis. Although some D. noxia defended themselves when attacked, aphid defense did not reduce parasitism by either wasp species. Thus, neither difference in the efficacy of aphid defense nor difference in oviposition behavior can explain greater parasitism by A. asychis in the field.

Response of an aphid parasitoid, Aphelinus asychis to its host, plant, host‐plant complex, and to malathion

Abstract Aphelinus asychis (Walker) can be valuable as a biocontrol agent of the aphid, Schizaphis graminum (Rondani), a major pest on grain crops in the United States. This study reports the wind tunnel, and olfactometric responses of this parasitoid to the host (aphid), plant (sorghum), and host‐plant complex (aphid‐infested sorghum). In addition, the parasitoids' response to malathion‐treated plants is also presented. The goal of the present study was to test the hypothesis that volatiles associated with the host attract natural enemies, as reported in cases of many hymenopterous parasitoids, and also to learn about the effects of insecticides on these parasitoids. In wind tunnel studies, these parasitoids moved upwind in the direction of the host‐infested plant. There was no direct flight observed, however, these parasitoids were observed to hop and jump, and sometimes walk to their host. In the olfactometer experiments, we found that A. asychis is attracted to host‐plant complex. The parasitoids' response to malathion in the olfactometer suggested that a malathion formulation when applied to plants can lure these beneficials, thus providing new insight into the ongoing task of integrating chemical and biological control of insect pests.

Does time until mating affect progeny sex ratio? A manipulative experiment with the parasitoid wasp Aphelinus asychis

AbstractIn haplodiploid organisms, unmated or sperm depleted females are “constrained” to produce only male progeny. If such constrained females reproduce, the population sex ratio will shift toward males and unconstrained females will be selected to produce more females. Assuming that a female's own time spent constrained is an index of the population‐wide level of constrained oviposition, and that constrained and unconstrained females reproduce at the same rate, the proportion of sons that females produce when unconstrained should decrease with increasing time spent constrained. Alternatively, if females cannot measure time spent constrained or if time spent constrained is not an index to the level of constrained oviposition in the population, the proportion of sons among progeny produced when unconstrained should not depend upon time spent constrained and should be female biased to an extent depending upon the average time spent constrained over evolutionary time. To test these predictions, we manipulated the amount of time spent virgin in the parasitoid wasp Aphelinus asychis Walker (Hymenoptera: Aphelinidae) and measured the number of males and females among progeny produced before and after mating. First, we found no interaction between age and age at mating in their effect on fecundity, which suggests that mating does not change fecundity. Second, we found that females mated at 8 days and 15 days produced equal sex ratios after mating but these were slightly more female biased than the sex ratios of females mated at 1 day. This observed “step response” suggests that females may perceive time from emergence to mating as a discrete rather than a continuous variable (i.e., short versus long), or that females do not perceive time per se but assess their age class (i.e., young versus old) at the time of mating.

Male orientation to trail sex pheromones in parasitoid wasps: does the spatial distribution of virgin females matter?

We studied male locomotory response to trails and patches of sex pheromone (left respectively by free-ranging females and females constrained to stay on a small area) in the two parasitoids Aphelinus asychis (Hymenoptera: Aphelinidae) and Trichogramma brassicae (Hymenoptera: Trichogrammatidae). Under the hypothesis that the spatial distribution of virgin females differs between these species (scattered among host plants in A. asychis, gregarious at emergence sites in T. brassicae), we predicted that male locomotory response to their sex pheromones should also differ: A. asychis males should follow pheromone trails on plants in order to encounter the females along these trails, whereas T. brassicae males should stay on pheromone patches, at emergence sites, and mate the females on these patches. Using an improved video-tracking system, we found that males of both species respond to conspecific sex pheromone trails and patches, but that the response does not differ much between species. Males released on marked substrates walked in a more convoluted pattern (i.e. higher path fractal dimension and higher number of crossings within tracks) than males released on unmarked substrates. On pheromone patches, males turned persistently in the same direction when leaving the patch, which explains a higher number of visits on marked patches than on unmarked patches, and possibly, higher track convolution on pheromone trails. Contrary to our hypothesis, male A. asychis did not follow female trails more accurately than male T. brassicae, and male T. brassicae did not stay longer on pheromone patches than male A. asychis. We argue that these discrepancies between our predictions and the observed responses originates from discrepancies between the assumed spatial distribution of virgin females and their actual distribution in the wild.

Does time until mating affect progeny sex ratio? A manipulative experiment with the parasitoid wasp

In haplodiploid organisms, unmated or sperm depleted females are to produce only male progeny. If such constrained females reproduce, the population sex ratio will shift toward males and unconstrained females will be selected to produce more females. Assuming that a female's own time spent constrained is an index of the population-wide level of constrained oviposition, and that constrained and unconstrained females reproduce at the same rate, the proportion of sons that females produce when unconstrained should decrease with increasing time spent constrained. Alternatively, if females cannot measure time spent constrained or if time spent constrained is not an index to the level of constrained oviposition in the popUlation, the proportion of sons among progeny produced when unconstrained should not depend upon time spent constrained and should be female biased to an extent depending upon the average time spent constrained over evolutionary time. To test these predictions, we manipulated the amount of time spent virgin in the parasitoid wasp Aphelinus asychis Walker (Hymenoptera: Aphelinidae) and mea-

Acute and Sublethal Activity of the Entomopathogenic Fungus Paecilomyces fumosoroseus (Deuteromycotina: Hyphomycetes) on Adult Aphelinus asychis (Hymenoptera: Aphelinidae)

In order to be most effective, components of integrated pest management programs should act in concert with minimal antagonistic interaction between natural enemy groups and other interventions. Entomopathogenic fungi and insect natural enemies have the potential to complement or interfere with one another, depending on environmental conditions. The acute and sublethal effects of the hyphomycete fungus, Paecilomyces fumosoroseus (Wize) Brown & Smith, on adult female Aphelinus asychis Walker, a common parasitoid of the Russian wheat aphid, Diuraphis noxia (Mordvilko), were studied under conditions of low (a55% RH) and high (≥95% RH) humidity at 24°C. Parasites exposed to dosages of P. fumosoroseus ranging from 3.75 to 3.75 × 103 conidia per square centimeter and incubated at 24°C in low or high relative humidity responded with mortality ranges of 20–33% and 33–88%, respectively. The effect of treatment with P. fumosoroseus at 5.2 × 104 spores per square centimeter (2× LC95 for D. noxia ) on foraging behavior of the parasitoid was studied with video image analysis 24–96 h after treatment with the fungus and incubation at low or high relative humidity. There was no significant difference between control and fungus-treated females that were incubated at the lower humidity in terms of percentage of time walking, turning, resting, and average walking speed. However, fungus-treated insects that were incubated at high relative humidity were significantly less active than their respective controls for percentage of time walking, walking speed, and distance covered. Also, average walking speed and distance walked by treated parasitoids incubated at low relative humidity for 96 h following treatment was significantly greater than treated insects incubated at the high relative humidity. Females treated with 2.6 × 104 spores per square centimeter and held in ≥95% RH for 24 h followed by incubation at 60% RH survived for an average of 5.7 d relative to 9 d for untreated females. The number of mummies produced per female per day was not significantly different between treated and untreated females, but more aphids were parasitized by the control insects due to longer survival. The limited untoward effect of P. fumosoroseus on adult A. asychis under conditions of lower humidity indicates good potential for their combined use for control of the Russian wheat aphid.

Temperature Dependence in Locomotion of the Parasitoid Aphelinus asychis (Hymenoptera: Aphelinidae) from Geographical Regions with Different Climates

In biological control, introduction of insect agents from regions with similar climatic conditions to those of the target host habitat have been an important consideration for successful implementation. Yet, there is little documentation of genetic variation in response to climate among natural enemy populations. In experiments on Aphelinus asychis Walker collected from China, France, and Morocco for release against Diuraphis noxia (Mordvilko) in North America, the relationship between locomotion (i.e., mean and maximum walking speeds and proportion of time walking) and temperature did not differ among geographical regions with different climates. Mean and maximum walking speeds increased with temperature from 8.5 to 28.5°C. Mean walking speed increased with hind tibia length, and because hind tibia length varied among geographical regions, it was used as a covariate in analyses comparing regions. Our results suggest that although locomotion depended on temperature, this dependence has not led to selection for adaptation to different temperature regimes. Thus, for mean and maximum walking speeds and proportion of time walking, insects collected from all 3 geographical areas were suited to the same climate.

Responses of Female Aphelinus asychis (Hymenoptera: Aphelinidae) and Aphidius matricariae (Hymenoptera: Aphidiidae) to Host and Plant-Host Odors

Field surveys showed previously that mummies of Diuraphis noxia (Mordvilko) parasitized by Aphelinus asychis Walker were 3-fold more abundant than those parasitized by Aphidius matricariae Haliday in a region where these species are endemic. We carried out a series of olfactometer experiments to test whether this difference in parasitoid abundance might arise from differences in attraction to host or host-plant odors. We used a 4-way olfactometer to measure choices among 4 odor sources—filtered air, barley ( Hordeum vulgare L.), D. noxia , and D. noxia plus barley—and the time spent in these 4 odor fields. Field-collected and laboratory reared A. asychis females did not move preferentially toward D. noxia or D. noxia –barley odors compared with filtered air or barley odors. This lack of preference was not affected by experience in which parasitoid females were allowed to oviposit in D. noxia on barley before being tested. However, after such experience, A. asychis females spent more time in the D. noxia –barley odor field than in the other odor fields. In contrast, naive A. matricariae females chose D. noxia –barley odors over other odors, and experienced A. matricariae females chose odors from D. noxia alone, as well as odors from barley plus D. noxia , over filtered air and barley odors. A. matricariae females spent more time in the D. noxia odor field than in the other odor fields, whether or not they were experienced with the plant–host complex. These results suggest that greater attraction to D. noxia cannot explain the greater abundance of A. asychis found on this host in the field.

Individual and combined effects of the fungus, Paecilomyces fumosoroseus and parasitoid, Aphelinus asychis Walker (Hym., Aphelinidae) on confined populations of Russian wheat aphid, Diuraphis noxia (Mordvilko) (Hom., Aphididae) under field conditions

AbstractThe natural enemies of Diuraphis noxia (Russian wheat aphid) can play an important role in the dynamics of aphid populations. The aphelinid wasp parasite, Aphelinus asychis, and the hyphomycete fungus, Paecilomyces fumosoroseus, were evaluated separately and in combination against confined populations of D. noxia under field conditions. Groups of 10 infested barley plants were treated in a spray tower with either 10 ml of a fungal suspension (1.7 × 107conidia/ml) [with and without incubation for 24 h under ideal conditions (Pfr; Pfr(24 h), respectively)] or four female A. asychis (Aa) or both fungus and parasitoids (Pfr + Aa). Insects treated with Pfr + Aa or Aa responded with higher mortality at 7 and 10 days post‐treatment than controls or those receiving only the fungus. Laboratory studies confirmed mycosis in cadavers of D. noxia that were recovered from plants that had received fungal treatments ranged from 24.4 to 31.9% (Pfr); 26.6 to 43.3% (Pfr(24 h)) and 27.7 to 34.5% (Pfr + Aa). The total number of living aphids per plant was significantly lower in the treatments involving A. asychis than in all other treatments and controls throughout the test. Significantly lower numbers of D. noxia relative to controls were also observed 13 days post‐treatment for the Pfr(24 h) treatment. At the termination of the test 13 days post‐treatment, the density of aphids on plants treated with Pfr + Aa, Aa, Pfr(24 h) and Pfr was 38.2%, 43.1%, 70.5% and 91.9% of that observed on control plants, respectively. Significant differences in the percentages of aphid age groups were observed between treatments involving A. asychis and all other treatments and controls 13 days post‐treatment; there was a significant reduction of the percentage of younger instar and relative increase in older instars for the treatments involving A. asychis. The dry weight of plants treated with Pfr + Aa was significantly greater than controls 13 days post‐treatment. These studies reveal an additive effect of P. fumosoroseus and A. asychis with regard to aphid control with no detrimental effects on the percentage of parasitism nor parasitoid emergence when the two agents were used together.

Reproductive Compatibility, Mating Behavior, and Random Amplified Polymorphic Dna Variability in Some Aphelinus asychis (Hymenoptera: Aphelinidae) Derived from the Old World

Reproductive compatibility, mating behavior, and random amplified polymorphic DNA (RAPID) variability were examined in samples of Aphelinus asychis obtained during foreign exploration for natural enemies of the Russian wheat aphid, Diuraphis noxia (Mordvilko). All specimens were reared initially from Diuraphis sp. collected at several Mediterranean basin localities and 2 localities in Central Asia. Using 7 laboratory cultures, we found 3 reciprocally and completely incompatible groups: the 1st group was represented by a culture from northcentral China, the 2nd group by a Kazakhstani culture, and a 3rd by 5 cultures from the Mediterranean basin (i.e., France, Greece, Morocco, Sicily, and Spain). One instance of partial, 1-way incompatibility was detected among the Mediterranean basin cultures. Behavioral experiments with 3 cultures showed that males respond to the sex pheromone of incompatible females and actively court them. However, females usually did not stop moving or elevate their abdomens in response to courtship by incompatible males. With 1 exception, genital contact and sperm transfer did not occur in incompatible pairings. Thus, rejection of incompatible males or failure to recognize incompatible males by females appeared to be 1 cause of incompatibility. In the exceptional case (Chinese males paired with Kazaklistani females), sperm transfer occurred but at significantly lower frequencies than in control pairings. Phenetic analysis of 61 RAPD loci in 6 laboratory cultures and 3 field samples from the Mediterranean basin delineated the same 3 groups as the compatibility experiment. Further work examining the geographic range, host range, and morphology of the incompatible groups is needed to clarify their taxonomic status.

Suitability of Random Amplified Polymorphic DNA for Genetic Markers in the Aphid Parasitoid, Aphelinus asychis Walker

Abstract The repeatability, variability, transmission, and linkage relationships of random amplified polymerphic DNA (RAPD) fragments were examined using six inbred lines of the haplodiploid parasitoid, Aphelinus asychis, originally collected on one date from a single held in southern France. Repeatability of RAPD fragments could be adequately judged using two replicate amplifications of the same individual in the same amplification run. Thirty-one of 136 repeatable fragments generated by 14 primers were polymorphic among lines. Segregation ratios in Fz males did not differ from 1:1 and extrachromosomal transmission was not observed. However, 5 nonparental bands that would increase the apparent number of loci by 16.2% in outbreeding populations were detected in hybrid F 1 females. In addition, linkage analysis indicates that the 31 polymorphic bands represent 19 presence-absence loci and 6 biallelic, fragment length polymorphism (FLP) or FLP-like loci. Four linkage groups were detected. Our main conclusion is that RAPD polymerphisms cannot be used as genetic markers unless information identifying nonparental bands and FLP and FLP-like loci is obtained. This information can be obtained during the course of typical population surveys in haplodiploid species because of male haploidy. In diploid species though, crossing experiments or DNA hybridization tests to establish homology are necessary prior to working with unpedigreed populations.

Mate finding via a trail sex pheromone by a parasitoid wasp.

In field observations and laboratory experiments, we found that virgin females of the solitary parasitoid Aphelinus asychis did not emit a volatile sex pheromone to attract males, contrary to what has been reported in many other parasitoid species. Instead, we found that virgin females deposited a sex pheromone on the substrate to which males responded by intensively searching on and near the marked area. Males did not respond to leaves exposed to mated females or to other males. In patches of 64 wheat leaves, males were dispersed from a central release point, and more males were subsequently observed on leaves exposed to virgin females than on unexposed leaves. The pheromone faded to inactivity in less than 24 h. To examine whether the trail pheromone would be sufficient for mate finding by males in the field, we modeled random movement of males among plant stems where the trail pheromone was the only cue males used to find females. The probability that females encountered at least one male in their lifetime increased with male density and time after female emergence. Given the range of densities of A. asychis in barley and wheat fields near Montpellier, France, the model generated an encounter probability sufficient to explain the survival of established populations. The model also suggested that difficulty in finding mates at low density might be a problem for invading populations.