Dynamic host-feeding and oviposition behavior of an aphid parasitoid <Emphasis Type="Italic">Aphelinus asychis</Emphasis>

In order to maximize the lifetime reproductive success of parasitoids, they should be induced to dynamically accept individual hosts that have different suitability for oviposition. Parasitoids tend to exhibit higher host-selective behavior when their egg load is limited, and are less selective if they are facing time constraints. Here, we evaluated the effects of parasitoid age on egg load, fecundity and host instar preference of a honey-fed aphid parasitoid, Aphelinus asychis Walker (Hymenoptera: Aphelinidae). Host selective experiment was conducted to measure host-preference of honey-fed A. asychis females at different ages, using the second and fourth instars of the green peach aphid Myzus persicae as their hosts. The results showed that the choice of host-instar for oviposition was significantly influenced by the parasitoid age. Honey-fed parasitoids in the age groups of 1, 5, 10 and 20 days tended to parasitize predominantly second-instar aphids, whereas 15-days old parasitoids showed no significant preference of host instars. On the other hand, host-feeding preference was not affected by parasitoid age. Parasitoid females of all ages preferred younger aphids to older aphids. This result could help evaluate the effectiveness of A. asychis for biological control of M. persicae when they encountered mixed-instar aphids in the field. In addition, the results might be helpful in assessing the host killing effects of other host-feeding parasitoids.     

Ecology of the aphid pests of protected pepper crops and their parasitoids

Myzus persicae, Macrosiphum euphorbiae, Aphis gossypii and Aulacorthum solani (Homoptera: Aphididae) are principal pests of protected pepper crops in southeastern Spain. Our goal was to determine the incidence of aphids on pepper crops and the role of vegetation surrounding greenhouses as a source of aphids and their parasitoids. The population dynamics were followed in six commercial greenhouses during 3 years. Another 82 greenhouses and their surrounding vegetation were surveyed occasionally. Myzus persicae had the highest incidence in pepper greenhouses followed by M. euphorbiae and A. solani. Parasitism of all aphid species in greenhouses was low, Aphidius matricariae and Aphidius colemani being the most abundant parasitoids. Myzus persicae and Macrosiphum euphorbiae were the most abundant and polyphagous aphids, being present on 77 and 55% of the plants sampled outside greenhouses, respectively; species of Brassicaceae were the main hosts for both aphids. Aulacorthum solani was only present on Malva parviflora and at low numbers. Outside greenhouses, A. matricariae was the most common parasitoid of M. persicae, followed by Diaeretiella rapae and A. colemani. Aphidius matricariae was the most polyphagous, being present in 10 out of 22 aphid species. Macrosiphum euphorbiae and A. solani were both parasitised by A. ervi and Praon volucre. Aphelinus asychis was found on A. solani. Parasitoids were found in other aphids not attacking pepper. The role of natural vegetation as a reservoir of aphid pests of pepper and of parasitoids is discussed.     

Functional responses of aphid parasitoids,Aphidius colemani (Hymenoptera: Braconidae) and Aphelinus asychis (Hymenoptera: Aphelinidae)

We evaluated the functional responses of two aphid parasitoids: Aphidius colemani on the green peach aphid Myzus persicae (Hemiptera: Aphididae), and Aphelinus asychis on M. persicae and the potato aphid, Macrosiphum euphorbiae (Hemiptera: Aphididae). Parasitoid oviposition occurred at host densities of 5, 10, 20, 30, 50, 80 or 100 aphids for A. colemani and 5, 10, 20, 30 or 50 aphids for A. asychis. More M. persicae were parasitized by A. colemani than by A. asychis at an aphid density of 50. Among the three types of functional response, type III best described the parasitoid response to the host densities both in A. colemani and A. asychis. The estimated handling time was shorter for A. colemani than for A. asychis (0.017 and 0.043 d, respectively). The proportion of aphids that were parasitized exhibited the same characteristic curve among the three host-parasitoid combinations: a wave form that appeared to be a composite of a decelerating (as in type II) response at low host density and an accelerating-and-decelerating (as in type III) response at medium to high host density. We hypothesize that the novel host species (and its host plant), density-dependent superparasitism, and/or density-dependent host-killing may have induced the modified type III response.     

On the effect of the food ofMyzus persicae Sulz. on the hymenopterous parasiteAphelinus asychis Walker

Summary The effect of different synthetic diets of the hostMyzus persicae on the parasiteAphelinus asychis was tested. Deficient diets were prepared by reducing sucrose or iron concentration: sucrose concentration was reduced from 15% in the complete diet (D.I.) to 7.5% in D. II and 3.75% in D. III; that of iron from 0.0023% in D. I to 0.0011% in D. IV and 0% in D.V.The development of the immature stages ofA. asychis in aphids fed on the deficient diets was delayed (especially on D. V). The size of the emerging adults was small, which corresponds with the reduced size of the host. The percentage of the male parasites was found to be higher on the deficient diets than on the full one. The lowest average longevity of the females was found among those reared on aphids on D. III and D.V.If honeydew fromM. persicae was offered to the females, a marked reduction in the longevity of these parasites was observed on D. II and D. III. On the other hand, on honeydew from aphids on D. IV and D.V,A. asychis lived as long as on honeydew from those fed on D.I.The fecundity of the females ofA. asychis was found to be dependent on the food composition of the hosts during larval development as well as during adult life.     

Females of Cotesia vestalis,a parasitoid of diamondback moth larvae,learn to recognise cues from aphid‐infested plants to exploit honeydew

1. To maximise their reproductive success, the females of most parasitoids must not only forage for hosts but must also find suitable food sources. These may be nectar and pollen from plants, heamolymph from hosts and/or honeydew from homopterous insects such as aphids. 2. Under laboratory conditions, females of Cotesia vestalis, a larval parasitoid of the diamondback moth (Plutella xylostella) which does not feed on host blood, survived significantly longer when held with cruciferous plants infested with non‐host green peach aphids (Myzus persicae) than when held with only uninfested plants. 3. Naïve parasitoids exhibited no preference between aphid‐infested and uninfested plants in a dual‐choice test, but those that had been previously fed aphid honeydew significantly preferred aphid‐infested plants to uninfested ones. 4. These results suggest that parasitoids that do not use aphids as hosts have the potential ability to learn cues from aphid‐infested plants when foraging for food. This flexible foraging behaviour could allow them to increase their lifetime reproductive success.     

An Aphelinid Species,Aphelinus asychis Walker (Hymenoptera: Aphelinidae) New to Korea

An aphid-attacking parasitoid, Aphelinus asychis Walker, which was reared from Myzus persicae (Sulzer) on Chinese cabbage, is reported for the first time in Korea.     

Intraguild predation on the aphid parasitoid <Emphasis Type="Italic">Aphelinus asychis</Emphasis> by the ladybird <Emphasis Type="Italic">Harmonia axyridis</Emphasis>

We investigated intraguild predation (IGP) on an aphid parasitoid, Aphelinus asychis Walker (Hymenoptera: Aphelinidae), by the multicolored Asian ladybird, Harmonia axyridis (Pallas) (Coleoptera: Coccinellidae), and used the green peach aphid, Myzus persicae (Sulzer) (Hemiptera: Aphididae) as the prey/host in the laboratory. The ladybirds reared on artificial diet and on aphids consumed more aphids than mummies, while those reared on parasitized aphids consumed similar numbers of aphids and mummies. The ladybirds chose more mummies in treatments when mummies were more abundant, and more aphids when numbers of aphids and mummies were equal, or when aphids were more abundant. However, at all density treatments, rejection rates of mummies (36%) were much greater than of aphids (2%). H. axyridis prey on more aphids than A. asychis mummies, which enhances biological control by the two species. However, prior feeding experience affected subsequent choice, increasing the competition between natural enemies which would reduce their combined effectiveness for biological control.     

Biological control of Myzus persicae (Hemiptera: Aphididae) through banker plant system in protected crops

Banker plants with Aphidius colemani were tested in greenhouse for control of Myzus persicae on arugula and sweet pepper crops and compared to inoculative releases of parasitoids. Banker plants system consisted of pots of oat (non-crop plant) infested with Rhopalosiphum padi (non-pest herbivore). The non-pest herbivore serves as an alternative host for A. colemani (parasitoid of the target crop pest). In the arugula crop significant differences in the pest population between the two strategies of biological control showed the lowest densities of the pest when introducing the banker plant system. In the sweet pepper crop, there was no difference in the pest population between the two strategies of biological control.     

3种寄主上桃蚜的选择性及形态分化

桃蚜是一种重要的农业害虫,寄主广泛,种下分化复杂。以采自黄土高原旱作区桃树、烟草、甘蓝上的桃蚜为研究对象,通过叶片选择法、传统比较形态测定法研究了3种寄主上桃蚜的选择性及形态分化。结果表明:在3种寄主同时存在的情况下,烟草上的桃蚜嗜食烟草,表现为63.5%的桃蚜选择烟草叶,13.8%选择甘蓝叶,8.2%选择桃叶,而甘蓝和桃树上的桃蚜对原寄主没有表现出明显的嗜好性;从形态指标来看,3种寄主上的桃蚜在体长、触角末节长度、后足腿节长度、触角与体长的比例方面存在显著差异(P0.05),说明这几个特征可以作为区分这3种寄主上桃蚜的依据。综合分析可以初步认为黄土高原旱作区烟草上的桃蚜可能形成了寄主专化型-烟草型。     

Biological control of aphids in the presence of thrips and their enemies

Generalist predators are often used in biological control programs, although they can be detrimental for pest control through interference with other natural enemies. Here, we assess the effects of generalist natural enemies on the control of two major pest species in sweet pepper: the green peach aphid Myzus persicae (Sulzer) and the western flower thrips Frankliniella occidentalis (Pergande). In greenhouses, two commonly used specialist natural enemies of aphids, the parasitoid Aphidius colemani Viereck and the predatory midge Aphidoletes aphidimyza (Rondani), were released together with either Neoseiulus cucumeris Oudemans, a predator of thrips and a hyperpredator of A. aphidimyza, or Orius majusculus (Reuter), a predator of thrips and aphids and intraguild predator of both specialist natural enemies. The combined use of O. majusculus, predatory midges and parasitoids clearly enhanced the suppression of aphids and consequently decreased the number of honeydew-contaminated fruits. Although intraguild predation by O. majusculus on predatory midges and parasitoids will have affected control of aphids negatively, this was apparently offset by the consumption of aphids by O. majusculus. In contrast, the hyperpredator N. cucumeris does not prey upon aphids, but seemed to release aphids from control by consuming eggs of the midge. Both N. cucumeris and O. majusculus did not affect rates of aphid parasitism by A. colemani. Thrips were also controlled effectively by O. majusculus. A laboratory experiment showed that adult predatory bugs feed on thrips as well as aphids and have no clear preference. Thus, the presence of thrips probably promoted the establishment of the predatory bugs and thereby the control of aphids. Our study shows that intraguild predation, which is potentially negative for biological control, may be more than compensated by positive effects of generalist predators, such as the control of multiple pests, and the establishment of natural enemies prior to pest invasions. Future work on biological control should focus on the impact of species interactions in communities of herbivorous arthropods and their enemies.     

A Dietary Test of Putative Deleterious Sterols for the Aphid Myzus persicae

The aphid Myzus persicae displays high mortality on tobacco plants bearing a transgene which results in the accumulation of the ketosteroids cholestan-3-one and cholest-4-en-3-one in the phloem sap. To test whether the ketosteroids are the basis of the plant resistance to the aphids, M. persicae were reared on chemically-defined diets with different steroid contents at 0.1–10 µg ml⁻¹. Relative to sterol-free diet and dietary supplements of the two ketosteroids and two phytosterols, dietary cholesterol significantly extended aphid lifespan and increased fecundity at one or more dietary concentrations tested. Median lifespan was 50% lower on the diet supplemented with cholest-4-en-3-one than on the cholesterol-supplemented diet. Aphid feeding rate did not vary significantly across the treatments, indicative of no anti-feedant effect of any sterol/steroid. Aphids reared on diets containing equal amounts of cholesterol and cholest-4-en-3-one showed fecundity equivalent to aphids on diets containing only cholesterol. Aphids were reared on diets that reproduced the relative steroid abundance in the phloem sap of the control and modified tobacco plants, and their performance on the two diet formulations was broadly equivalent. We conclude that, at the concentrations tested, plant ketosteroids support weaker aphid performance than cholesterol, but do not cause acute toxicity to the aphids. In plants, the ketosteroids may act synergistically with plant factors absent from artificial diets but are unlikely to be solely responsible for resistance of modified tobacco plants.     

Hyperpredation by generalist predatory mites disrupts biological control of aphids by the aphidophagous gall midge Aphidoletes aphidimyza

Biological control of different species of pest with various species of generalist predators can potentially disrupt the control of pests through predator-predator interactions. We evaluate the impact of three species of generalist predatory mites on the biological control of green peach aphids, Myzus persicae (Sulzer) with the aphidophagous gall midge Aphidoletes aphidimyza (Rondani). The predatory mites tested were Neoseiulus cucumeris (Oudemans), Iphiseius degenerans (Berlese) and Amblyseius swirskii Athias–Henriot, which are all commonly used for pest control in greenhouse sweet pepper. All three species of predatory mites were found to feed on eggs of A. aphidimyza, even in the presence of abundant sweet pepper pollen, an alternative food source for the predatory mites. In a greenhouse experiment on sweet pepper, all three predators significantly reduced population densities of A. aphidimyza, but aphid densities only increased significantly in the presence of A. swirskii when compared to the treatment with A. aphidimyza only. This stronger effect of A. swirskii can be explained by the higher population densities that this predator reached on sweet pepper plants compared to the other two predator species. An additional experiment showed that female predatory midges do not avoid oviposition sites with the predator A. swirskii. On the contrary, they even deposited more eggs on plants with predatory mites than on plants without. Hence, this study shows that disruption of aphid control by predatory mites is a realistic scenario in sweet pepper, and needs to be considered when optimizing biological control strategies.     

Control of Aphis gossypii and Myzus persicae (Hemiptera: Aphididae) by a flightless strain of Harmonia axyridis (Coleoptera: Coccinellidae) on green pepper plants in open fields

The cotton aphid Aphis gossypii Glover and the green peach aphid Myzus persicae (Sulzer) are economically important pests with a worldwide distribution. We evaluated the efficacy of releasing a flightless adult strain of the multicolored Asian lady beetle Harmonia axyridis (Pallas) as a control measure against these aphids on green pepper plants in open fields. Flightless H. axyridis adults were observed on the green pepper plants in the releasing plots throughout the experimental period and were found to be effective biocontrol agents, markedly decreasing the numbers of aphids. These results suggest that adults of this flightless strain of H. axyridis are effective in controlling aphids on green pepper plants in open fields.     

Different pepper cultivars affect performance of second (Myzus persicae) and third (Diaeretiella rapae) trophic levels

While chemical application can control aphid outbreaks, the overuse of insecticides can make aphids more resistant to these insecticides. These effects make strategies such as host plant resistance combined with biological control agents as an important part of alternative control methods. In this study, the performance of the green peach aphid Myzus persicae (Sulzer) (Hemiptera: Aphididae) and its parasitoid wasp, Diaeretiella rapae (McIntosh) (Hymenoptera: Braconidae) were determined on different pepper cultivars (California, Hamedan, Minab, Sabz-Farangi, Sabz-Ghalami, Semnan, Shahroud, and Tehran) in a growth chamber at 25 ± 1 °C, 60 ± 5% RH and a 16:8 h L:D photoperiod. The intrinsic rate of increase (r) of the aphid on the above-mentioned cultivars was 0.3203, 0.3891, 0.3594, 0.3152, 0.3512, 0.3032, 0.3352 and 0.2787 day⁻¹, respectively. Comparison of the intrinsic rate of increase (r) on different pepper cultivars revealed that Hamedan was the most susceptible and Tehran was the most resistant cultivar. The parasitoids reared on the aphids fed on the susceptible cultivar (Hamedan) had a higher intrinsic rate of increase (0.2641 day⁻¹) than those (0.2259 day⁻¹) reared on the resistant cultivar (Tehran). These results demonstrated that the quality of host plant affected the performance of M. persicae and its parasitoid D. rapae.     

The effect of pre-acquisition starvation on aphid transmission of potyviruses during observed and electrically recorded stylet penetrations

The effect of pre-acquisition starvation on stylet penetration behaviour by the aphidMyzus persicae (Sulz.) and the consequent non-persistent transmission of the potyviruses beet mosaic virus (BMV) and potato virus Y (PVY) were investigated. Visual observations indicated that starved aphids initiated penetrations earlier and penetrated for shorter periods than non-starved insects. Tethering with a fine gold wire did not affect these observations with either starved or non-starved aphids, but starvation caused increased PVY and BMV acquisition efficiency, regardless of tethering. Tethered aphids were then made part of an electrical circuit and their stylet activities investigated in detail. Electrically recorded aphids also acquired and inoculated both potyviruses more efficiently when starved, and these acquisitions and inoculations were associated with stylet punctures of plant cell membranes. However, starvation did not affect the occurrence of electrically recorded membrane puncture, suggesting that non-behavioural factors may contribute to the enhancement of virus transmission by pre-acquisition starvation.     

Effect of cultivars with varying levels of resistance to aphids on development time,sex ratio,size and longevity of the parasitoid <Emphasis Type="Italic">Aphidius colemani</Emphasis>

The influence of cultivars of common cabbage, Brassica oleracea var. capitata with varying levels of resistance to Brevicoryne brassicae (L.) and Myzus persicae (Sulzer) on key biological characteristics of Aphidius colemani (Viereck) was investigated under laboratory conditions. The total development time for female parasitoids reared on M. persicae did not differ significantly between Minicole (green-leaved, partially resistant with antibiosis factors for B. brassicae) and Derby Day (green-leaved, susceptible to both aphid species); but development was significantly faster (ca 10%) on Ruby Ball (red-leaved, partially resistant with antixenosis factors for B. brassicae). Total development time for females reared on B. brassicae was slightly shorter on Ruby Ball than on Minicole. Males reared on M. persicae developed into adults significantly faster (ca 10%) on Ruby Ball than on Minicole. However, when B. brassicae was the host, no significant variations in development time were observed. Sex ratios, size and longevity of both male and female parasitoids on either host were not significantly influenced by cultivar. The results are discussed in relation to the compatible utilisation of host-plant resistance and biological control in the integrated management of aphids.     

Pollen increases fitness and abundance of Orius insidiosus Say (Heteroptera: Anthocoridae) on banker plants

Banker plants are intended to enhance biological control by sustaining populations of natural enemies. Banker plants do this by providing alternative sources of food for natural enemies, such as pollen for omnivorous predators, thus decreasing the likelihood of their starvation and emigration from a cropping system when pest populations are low or absent. A banker plant system consisting of the Black Pearl pepper, Capsicum annuum ‘Black Pearl’, and the omnivorous minute pirate bug, Orius insidiosus Say (Hemiptera: Anthocoridae) has recently been proposed to improve biological control of thrips. Therefore, we studied how pollen from the Black Pearl pepper plant affects O. insidiosus fitness and abundance through a series of laboratory and greenhouse experiments. We found that a mixed diet of pollen and thrips increased O. insidiosus female longevity, decreased nymphal development time, and yielded larger females compared to a diet of thrips alone. Furthermore, O. insidiosus abundance was greater on flowering pepper plants than non-flowering pepper plants. From these results, we suggest that pollen from Black Pearl pepper banker plants could increase adult O. insidiosus abundance for the purpose of biological control in two ways: (1) reduce starvation and increase longevity of O. insidiosus when prey is absent; (2) enhance O. insidiosus fitness and fecundity when prey is present by mixing plant and prey diets. These results encourage future studies with the Black Pearl pepper as a banker plant for improving biological control of thrips in commercial greenhouses.     

Age-Specific Functional Response of <Emphasis Type="Italic">Aphidius matricariae</Emphasis> and <Emphasis Type="Italic">Praon volucre</Emphasis> (Hymenoptera: Braconidae) on <Emphasis Type="Italic">Myzus persicae</Emphasis> (Hemiptera: Aphididae)

The green peach aphid, Myzus persicae (Sulzer), is one of the most important aphid pests on pepper. Aphidius matricariae Haliday and Praon volucre (Haliday) are known as biological control agents for aphids in vegetable crops. In this research, age-specific functional responses of these two parasitoids were evaluated on different densities of 2, 4, 8, 16, 32, and 64 green peach aphids. Type of functional response varied from type II to type III for different ages of A. matricariae, but type of functional response was not affected by female age for P. volucre. The functional response of P. volucre was determined as type II in the whole parasitoid lifetime. The searching efficiency (a), b, and handling time (T _h ) were estimated using the Rogers equations. The highest searching efficiency (a) and lowest handling time were observed during the first half of lifetime of A. matricariae and P. volucre. Aphidius matricariae and P. volucre caused reasonable mortality of the green peach aphid by parasitism of 52.17 and 47.05 host aphids, respectively, in 24 h. Therefore, they are suggested as suitable candidates for control of M. persicae in pepper greenhouses.     

Wing development and parthenogenesis induced in progenies of kinoprene-treated gynoparae of Aphis fabae and Myzus persicae

Presumptive gynoparae of Aphis fabae and Myzus persicae were exposed to various levels of kinoprene (Zoecon's ZR 777) by being placed as 4th-instar alatiform larvae on bean or radish seedlings that had been sprayed with different concentrations of kinoprene in an acetone-tween-water emulsion. Larvae exposed to the highest (0.1%) concentration tested developed into adults 1 to 2 days sooner than those on control plants. The adults on the treated plants had variously deformed wings, reduced sclerotization (and pigmentation in the case of M. persicae) and other apteriform features. On reaching adulthood the affected aphids settled to feed and started to larviposit some days earlier than the control aphids. After two weeks as adults, treated gynoparae of M. persicae produced more larvae than the 7 to 9 typically deposited by control gynoparae under the short-day and cool temperature conditions employed in these tests.Whereas most or all of the larvae produced by the control gynoparae developed into oviparae (apterous, egg-laying, sexual females), gynoparae exposed to 0.1% kinoprene-treated plants predominantly produced alatiform viviparous offspring. If the latter were allowed to develop on untreated plants they deposited a few oviparous larvae. Alatiform virginoparae of M. persicae (from the same holocyclic strain that produced the gynoparae) also responded to kinoprene by developing wing deformities and by producing alatiform offspring. In contrast, alatiform virginoparae from an androcyclic strain of M. persicae, although developing wing deformities, produced only apterous progeny.The stimulation by kinoprene of wing development and parthenogenesis in the progeny of treated gynoparae is discussed in the light of our present knowledge of these aspects of aphid polymorphism.     

Superparasitism and host discrimination byEphedrus cerasicola [Hym.: Aphidiidae], an aphidiid parasitoid ofMyzus persicae [Hom.: Aphididae]

Myzus persicae (Sulzer) at different densities (1 to 120 aphids) on a paprika plant in a 1.8 dm³ cage were exposed at 21°C to single females of the parasitoidEphedrus cerasicola Stary. Three different exposure periods were used: 1 hr, 6 hrs, 24 hrs. The aphids were dissected 6 days after parasitization. Superparasitism was measured as number of hosts superparasitized and number of parasitoid larvae per aphid. It attained a maximum around host density=5 and decreased with increasing host density and decreasing exposure time. Almost no superparasitism occurred during the 1st hour. A non-random larval distribution indicated thatE. cerasicola discriminates between unparasitized and parasitized aphids, but probably not between aphids with different numbers of parasitoid eggs. Larvae in superparasitized aphids developed slower than single larvae. The supernumerary larvae died during the 1st instar, probably killed by chemical means since no physical attacks between larvae have been observed.