The responses ofPraon spp. parasitoids to aphid sex pheromone components in the field

In autumn 1991, aphid parasitoids of the genusPraon (Hymenoptera; Braconidae) were caught in water traps with lures containing synthetic aphid sex pheromone components at three sites in England and one in Germany. At two of the English sites and at the German site, the traps were placed in winter cereal fields whilst the third English site was in woodland. Three species were caught,P. volucre, P. dorsale andP. abjectum. Those caught in cereal fields were almost entirelyP. volucre, whilstP. dorsale dominated at the woodland site. Of the known aphid sex pheromone components, the most effective lure was the (+)-(4aS, 7S, 7aR)-nepetalactone. Nepetalactone traps placed at the woodland site in spring and summer caught fewPraon females, and attraction may be confined to the autumn, when sexual female aphids are present in the field. Male parasitoids did not respond to the aphid pheromones at any time, although they were caught in suction traps operated at the woodland site during the autumn. At the cereal sites height had a significant influence on the efficiency of the pheromone traps, those placed just above the crop canopy being most effective. There was no evidence that any other genus of parasitoid responded to aphid sex pheromones at these sites.     

Host specialization in habitat specialists and generalists

Generalists and specialists use different cues to find their habitat and essential resources. While generalists have the advantage of exploiting a wider range of resources, they are predicted to be less efficient in using one particular resource compared to specialists. The level of specialization of parasitoids can be either at the habitat or at the host level; strategies used by either type are expected to differ. We examined interactions between three aphid parasitoid species that are a habitat specialist Aphidius rhopalosiphi, a habitat generalist Aphidius ervi, and a host generalist Praon volucre on three cereal aphids, Sitobion avenae, Metopolophium dirhodum and Rhopalosiphum padi. We compared total parasitism rate across behavioral and physiological variation in a non-choice test. Next, we addressed total parasitism in two phases to examine: (1) the response of parasitoids to different hosts through the behavioral sequence from antennation through oviposition, and (2) the physiological suitability of different hosts for oviposition and larval development. Parasitization typically involved the following behavioral steps: (1) antennal contact, (2) abdominal bending, and (3) ovipositor insertion (acceptance). A. rhopalosiphi had the same number of antennal contacts with the three aphids but showed fewer instances of abdominal bending towards R. padi. Pre-contact host preference was found for A. ervi but it did not correspond to the level of acceptance. The number of antennal contacts by P. volucre corresponded to the parasitization level of the aphid species but more mummies were produced on M. dirhodum than on R. padi. These results suggest that parasitoid species that are habitat specialists react similarly to the different host species present in the same habitat, whereas generalist species exhibit clear preferences during host selection. Preferences were, however, not always related to host suitability.     

Sex pheromone and visual trap interactions in mate location strategies and aggregation by host-alternating aphids in the field

Abstract. Field observations were made on the responses of males and gynoparae of three host-alternating aphid species, the blackberry-cereal aphid, Sitobion fragariae (Walker), the bird cherry-oat aphid, Rhopalosiphum padi (L.) and the damson-hop aphid, Phorodon humuli (Schrank) to species-specific sex pheromones released from transparent and coloured water traps.Pheromone traps caught significantly more males than did control traps without pheromone, whereas transparent, light green, yellow and orange traps caught most insects.Measurements of the distance over which sex pheromones function indicated that male P.humuli detect the pheromone 2–6 m from the source and can fly upwind to a source in wind speeds of 0.7 m s^-1.In all three species significantly more gynoparae were caught in pheromone traps than in control traps, suggesting that pheromone released by adult sexual females may assist late-flying gynoparae to locate a suitable host plant on which to deposit their progeny.The response is relatively stronger for males than gynoparae, but the pheromones appear to act as both sex and aggregation pheromones.     

Intimate Rendezvous in a Tritrophic Context? Nothing but the Girls for Male Lysiphlebus testaceipes

In insects, mating often occurs after natal dispersal, and hence relies on a coevolved combination of sexual communication and movement allowing mate encounter. Volatile sex pheromones are widespread, generally emitted by females and triggering in‐flight orientation of conspecific males. In parasitoid wasps, unmated females can start laying unfertilized eggs via parthenogenesis so that host patches could serve as sites of rendezvous for mating. Males could therefore use cues associated with host patches to focus their search on females that have successfully found oviposition sites. We hypothesized that in parasitoids exploiting herbivorous hosts, sex pheromones, and herbivore‐induced plant volatiles (HIPV) should act in synergy, triggering male orientation toward ovipositing females. We tested this hypothesis with the aphid parasitoid Lysiphlebus testaceipes. Results from both field and laboratory experiments show that males are strongly attracted to virgin females, but that volatiles from aphid‐infested plants have no effect on male orientation, neither has a cue, nor in interaction with the female sex pheromone. The absence of synergy between sex pheromones and HIPV contrasts with results on other species and raises interesting questions on mating systems and sexual selection in parasitoid wasps.     

Superparasitism limitation in an aphid parasitoid: cornicle secretion avoidance and host discrimination ability

Superparasitism avoidance by the endoparasitoid Aphidius rhopalosiphi De Stefani Perez on the grain aphid, Sitobion avenae was studied. Experiments were carried out in which aphids were exposed to two consecutive attacks by parasitoids. Results showed that superparasitism avoidance in A. rhopalosiphi was mediated by two successive stimuli whose effectiveness depended on the time interval between attacks. For short time intervals (<16 h), host rejections were mainly associated with the presence of dried cornicle secretion on the host's body which was exuded during the first attack. The repellency of this secretion declined with the time interval between attacks, becoming ineffective 2 days after the first parasitization, and allowed females to reject up to 30% of parasitized hosts. For longer time intervals (>/=16 h), host rejection behavior was a response of parasitoid females to internal changes in host quality associated with parasite development. This response gradually increased with an increase in time interval, reaching no more than 60%, 96 h after initial parasitization. This host discrimination ability did not allow females to distinguish between hosts parasitized by themselves or by conspecifics. Consequently, these findings suggest that superparasitism is a common event in A. rhopalosiphi and especially on recently parasitized hosts.     

Mate Finding Via a Trail Sex Pheromone by <Emphasis Type="Italic">Aphytis melinus</Emphasis> DeBach (Hymenoptera: Aphelinidae) Males

Finding mates is frequently problematic for parasitoid wasps. In some parasitoid species, males rely on volatile, airborne sex pheromones for locating mates, while in others they rely on contact, trail sex pheromones. This study sought to shed light on the mate finding mechanism of males of Aphytis melinus. Specifically, the goal was to determine whether A. melinus males use airborne or contact pheromones, or both, for locating mates. The study showed that A. melinus males rely on a contact, trail sex pheromone for locating mates: A. melinus males responded to substrate-borne cues left by virgin females, while they did not respond to airborne cues from virgin females. Specifically, males more frequently encountered virgin females when the females walked across an arena to a fixed encounter point compared to when they were manually placed at the encounter point, and spent greater than expected time on surfaces previously visited by virgin females compared to control surfaces not visited by females. In contrast, males did not respond to airborne cues from virgin females in an airflow olfactometer nor to traps baited with virgin females in the field, and spent similar lengths of time on surfaces visited by newly-mated or 24-h mated females versus control surfaces not visited by females. The main effect of the trail sex pheromone on the behavior of A. melinus males was to direct their search and, so, increase the likelihood of encountering mates. This effect apparently is not preceded by longer-range attraction of males via an airborne female sex pheromone. Overall, the results of this study support a hypothesis in which A. melinus males searching on substrates on which females may be present rely exclusively on a trail sex pheromone to locate mates.     

Evidence for the existence of a species closely related to the cereal aphid parasitoid Aphidius rhopalosiphi De Stefani-Perez based on host ranges, morphological characters, isoelectric focusing banding patterns, cross-breeding experiments and sex pheromone specificities (Hymenoptera, Braconidae, Aphidiinae)

Abstract. Host transfer trials with six strains of the cereal aphid parasitoid Aphidius rhopalosiphi De Stefani-Perez revealed the presence of two differing host ranges: three strains parasitized Sitobion uvenae (F.) and S.fragariae (Wlk.) exclusively, whereas the others successfully developed in both Sitobion species and also in Metopolophium dirhodum (Wlk.), M.festucue cerealiurn Stroyan, Rhopalosiphum padi (L.) and Diuraphis muehlei Börner. The two host range groups were poorly distinguishable by means of morphological characters. In con trast, isoelectric focusing proved to be a much better tool for discrimi nation. Reproductive isolation between the two host range groups was clear but not complete, as evidenced by crossing experiments with laboratory-bred and field-collected material. Under field conditions, males showed a specific response to virgin females of the two groups. Hence, the sex pheromones of the females were obviously different. Considering these results, a species ( Aphidius sp. A) closely related to A.rhopalosiphi seems to occur. As a detailed study of morphological characters is still lacking, Aphidius sp. A is not yet formally established here. Due to its dependence upon Sitobion spp., Aphidius sp. A may be an economically important parasitoid of the pest aphid S.avenae .     

Hopkins' 'host selection principle', another nail in its coffin

Abstract. Adult female parasitoids (Aphidius rhopalosiphi De Stef.) (Hymenoptera: Aphidiidae) reared on the aphid Metopolophium dirhodum (Walk.) (Homoptera: Aphididae) changed their responses to odours of two wheat cultivars ('Maris Huntsman' and 'Rapier') when the parasitized aphids had been moved from the former to the latter cultivar at various times after parasitization. If the aphids were moved after less than 6 days, the female parasitoids emerging from mummies by then formed on 'Rapier' responded positively to that cultivar, whereas parasitoids emerging from mummies transferred as still living aphids after 8 days on 'Maris Huntsman', responded positively to that cultivar rather than to 'Rapier' on which they had emerged. This appeared to be evidence for Hopkins' 'host selection principle', which states that chemical experience acquired by the larva of an endopterygote insect can be transferred through the pupal stage to the adult. However, discrimination in favour of either cultivar disappeared when the parasitoids were reared in aphids on both cultivars, and the emerging females were tested following excision of the pupae from the aphid mummies. The previous discrimination shown by adult parasitoids emerging from aphid mummies must therefore be determined by the chemicals contacted by a parasitoid on the skin of the mummy or while biting its way out of the dead aphid.     

The effect of natural enemies on the spread of barley yellow dwarf virus (BYDV) by Rhopalosiphum padi (Hemiptera: Aphididae)

The effects of two natural aphid enemies, adult Coccinella septempunctata Linneaus, a predator, and Aphidius rhopalosiphi de Stefani Perez, a parasitoid, on spread of barley yellow dwarf virus (BYDV) transmitted by the bird cherry-oat aphid, Rhopalosiphum padi (Linnaeus) were studied under laboratory conditions. Predators or parasitoids were introduced to trays of durum wheat seedlings and the patterns of virus infection were observed after two, seven and 14 days of exposure. More plants were infected with BYDV in control trays without A. rhopalosiphi than in trays with the parasitoid present, both seven and 14 days after the introduction of parasitoids. Patterns of virus infection were found to be similar over time in trays with a parasitoid present and in control trays. More plants were infected in trays with C. septempunctata present than in control trays, both two and seven days after the introduction of the coccinellid. The spread of virus infections progressed differently over time for the two treatments (predator and parasitoid), differences between treatments being most marked after two days and seven days, when more plants exposed to predators but fewer exposed to parasitoids were infected with BYDV compared to their respective controls. However, by the 14th day 88% of all plants were infected and there was no significant difference between the two treatments. The role of natural enemies in spread of BYDV is discussed.     

植物挥发性物质对蚜虫性信息素诱蚜效果的影响(英文)

本研究首先是在不同的寄主植物中利用蚜虫性信息素进行田间诱蚜实验。结果表明寄主植物影响性信息素田间诱蚜的种类和效果。在桃园 ,以蚜虫性信息素荆芥内酯和荆芥醇为性诱剂的水盆诱捕器 ,诱到 3种蚜虫的雄蚜 ,分别是桃蚜、桃粉大尾蚜和莲缢管蚜。其中 ,桃蚜占绝大多数 ,且还被性信息素的单一组分植物提取的荆芥内酯所吸引。麦田中诱到的雄蚜为麦二叉蚜。苹果园中诱到的雄蚜是绣线菊蚜和梨中华圆尾蚜 ,且性信息素诱捕器中的数目远多于对照诱捕器。据田间诱蚜实验结果推测 ,荆芥内酯和荆芥醇对桃粉大尾蚜有吸引作用 ,荆芥内酯可能是绣线菊蚜和梨中华圆尾蚜性信息素的一个组分。另外进行的田间实验表明寄主植物挥发性物质对蚜虫性信息素诱蚜效果有影响 ,当荆芥内酯诱捕器同时释放桃叶挥发物时 ,诱到的桃蚜雄蚜数量明显增加。触角电位记录实验也表明桃蚜雄蚜对桃叶挥发物和桃芽挥发物有反应。     

Efficacy of the parasitoid,Diaeretiella rapae (McIntosh) (Hymenoptera: Braconidae) against Myzus persicae (Sulzer) (Hemiptera: Aphididae) infesting rapeseed-mustard

Efficacy of Diaeretiella rapae (McIntosh) (Hymenoptera: Braconidae) was determined by studying its biological and behavioural attributes on the aphid, Myzus persicae (Sulzer) (Hemiptera: Aphididae). Total developmental duration of the parasitoid was longer in younger instars compared to that in older instars of aphid. Host age negatively affected the oviposition period and fecundity of the ovipositing parasitoid. Survival of the immatures was higher in older than the younger instars of the aphid. Sex ratio for the parasitoid was female-biased. Longevity of female parasitoid was higher while parasitizing aphid nymphs of younger age groups (1–2 days old) compared to that of older age groups (4–5 days old). Parasitoid showed a higher preference towards second instar of M. persicae both in choice and no-choice tests. Results on mutual interference revealed that per capita searching efficiency decreased from 0.91 to 0.07 as parasitoid densities increased from 1 to 8. Logistic regression exhibited a type II functional response for D. rapae. The estimated values of search-efficiency (a) and handling time (T_h) were 0.038 h⁻¹ and 1.59 h, respectively. The maximum parasitization rate was 15.08. This investigation suggests that D. rapae could be an effective candidate for augmentative biological control of M. persicae which infests several plant species of economic importance.     

The influence of aphids and honeydew on the leaving rate of searching aphid parasitoids from wheat plants

Dispersal cages were used to investigate the effects of aphids and treatment with artificial honeydew on the leaving rate of searching females of the parasitoid Aphidius rhopalosiphi from groups of wheat plants. Parasitoids which flew away from groups of plants placed in the centre of a cage were trapped on the sides and roof of the cage and thus were prevented from returning to the plants. The positions of trapped parasitoids suggested their direction of flight when dispersing from the plants. Parasitoids increased their residence times on groups of plants in the presence of aphids and of artificial honeydew, but the rate of parasitism of the host Sitobion avenae was not raised by the presence of artificial honeydew under the experimental conditions used. The direction of flight taken by the majority of parasitoids suggested that they were leaving the plants in order to locate further plants nearby to continue searching rather than to terminate searching and disperse away from the area. The need to consider plant patch size in studies of parasitoid searching behaviour is stressed.     

A survey of aphids and aphid parasitoids in cereal fields in Denmark, and the parasitoids' role in biological control

In 1996 and 1997 a field survey of the abundance and species composition of cereal aphid primary and secondary parasitoids in spring barley, winter wheat and durum wheat was conducted in Zealand, Denmark. The purpose was to create a better understanding of the mechanisms underlying aphid–parasitoid dynamics in the field. Such an understanding can be used when developing biological control methods in cereals. In both years aphid attacks in cereals began in late June and never exceeded the economic threshold. In 1996 the first aphids were found in wheat on 26 June; in 1997 the first aphids were found on 24 June on both crops. The highest densities reached in 1996 were an average of six aphids per shoot in winter wheat and one aphid per shoot in spring barley. In 1997 the highest densities reached were 11 aphids per shoot in winter wheat and four aphids per shoot in spring barley. The aphid population collapsed by the end of July to early August in 1996, but it collapsed by mid-July in 1997. The onset and peak of parasitization were delayed in comparison to aphid infestation. Parasitism was 20–60% by the end of the cropping season in spring barley, and 30–80% in winter wheat and durum wheat in 1996. In 1997 parasitism did not exceed 3–11% in barley and was less than 2% in one winter wheat field but more than 40% in the other winter wheat field sampled. In both years most parasitism was due to Aphidiidae (Hymenoptera). The two dominant species were Aphidius ervi Haliday and Aphidius rhopalosiphi De Stefani-Perez. Hyperparasitism began after primary parasitism and increased progressively during the cropping season. The two years were similar in many respects, including for species composition of aphids and parasitoids. The late start of the aphid infestation may have contributed to the high level of parasitization found in 1996, but in 1997 the aphid infestation period was so short that a parasitoid population did not have time to build up.     

蚜虫性信息素

蚜虫属同翅目蚜总科,是重要的农作物害虫。蚜虫长年行孤雌生殖,在中、高纬度深秋时,产生性蚜,以卵越冬。雌性蚜分泌性信息素荆芥内酯(nepetalactone)和荆芥醇(nepetalactol)。该文综述了蚜虫性信息素的结构与组分、性腺的形态结构、性信息素释放及影响因素;性信息素对雌性母和天敌的引诱作用;性信息素在蚜虫种间隔离中的地位和作用以及蚜虫性信息素在蚜虫防治中的应用前景。     

Reactions of adult female parasitoids, particularly Aphidius rhopalosiphi, to volatile chemical cues from the host plants of their aphid prey

Abstract. In Y-tube olfactometer tests, Aphidius ervi Hal., Trioxys sp., Praon sp., Aphelinus flavus (Nees), Lysiphlebus fabarum (Marsh.) and Aphidius rophalosiphi De Stef. responded positively to the odour of the plant on which aphid mummies containing them had been collected. The response to host plant odour was greater than the response to the odour of host aphids, their honeydew or a combination of the two. The strongest response was to a combination of plant and host aphids. A. rhopalosiphi showed a strong positive response to three wheat volatiles (cis-3-hexenyl acetate, cis-3-hexen-1-ol and trans-2-hexenal) as well as to indole-3-acetaldehyde (a breakdown product of tryptophan in aphid honeydew). In both olfactometer tests with odours and choice trials with whole plants, newly emerged A. rhopalosiphi distinguished and preferred the variety of wheat on which their development had occurred to other wheat varieties.     

Responses to aphid sex pheromones by the pea aphid parasitoids Aphidius ervi and Aphidius eadyi

Aphidius ervi and Aphidius eadyi, two parasitoids of the pea aphid Acyrthosiphon pisum, were attracted to components of the aphid sex pheromone in laboratory bioassays. Pre-test experience with host aphids in the presence of aphid sex pheromone did not affect the response of A. ervi to pheromone in a 4-way olfactometer, compared with that of naive parasitoids. Aphidius ervi females exposed only to the pheromone prior to testing did not respond in the olfactometer, suggesting habituation to the foraging cue by the parasitoid. In a wind tunnel, aphid sex pheromone increased the attraction of A. ervi to the plant-host complex (Vicia faba/A. pisum), suggesting an additive effect when two different foraging cues are present simultaneously.     

Pan trapping soybean aphids (Hemiptera: Aphididae) using attractants

Since its introduction into the United States in the past 10 yr, soybean aphid, Aphis glycines Matsumura (Hemiptera: Aphididae), has been a damaging pest to soybean, Glycine max (L.) Merrill. During 2008 and 2009, fields in central and north central Iowa experienced pockets of high soybean aphid populations. Electroantennograms have shown that soybean aphid alatae are capable of detecting host plant volatiles and sex pheromones. Here, we evaluated baited pan traps as a potential soybean aphid attractant. Yellow pan traps were placed in soybean fields after planting along with lures that contained plant volatiles and sex pheromones in 2008 or sex pheromones only in 2009. Pan trap contents were collected weekly, and plant counts also were conducted. Aphids were identified, and soybean aphids were counted to determine whether one chemical lure was more attractive to spring migrants than other lures. In both years, soybean aphids collected in pan traps with lures were not significantly different from the other products tested.     

Aphid parasitoids detect that an alien plant was present nearby during their development

Abstract Glasshouse and laboratory experiments were conducted with Aphidius rhopalosiphi parasitizing Metopolophium dirhodum to test whether the presence in the same environment of another plant species (tomato or marigold) induced aerial allelopathy in wheat plants.
Emerging parasitoids were offered the choice of two odours of wheat plants in an olfactometer – wheat grown alone and wheat grown in the presence of the second plant species.
Female parasitoids responded more strongly than males, but both sexes preferred the odour of wheat grown in the environment in which they had developed (i.e. with or without the second plant species present).
Moving the tomato plants from the cages where they had been placed with wheat to the cages that had previously had wheat alone just before the aphid mummy formed showed that the odour environment the emerging parasitoid responded to was that of the mummy rather than that of the developing parasitoid larva. From this it was concluded that the parasitoids in the olfactometer were responding not only to wheat volatiles, but also to tomato volatiles absorbed on the surface of the mummy and encountered by the emerging adult parasitoid.
By excising the parasitoid pupa from the mummy formed on one wheat cultivar, and offering the emerging parasitoids the surface of aphid mummies formed on a different cultivar, it was confirmed that olfactometer responses represented a learning of the chemistry of the surface of the mummy encountered at or after emergence.     

Vine mealybug sex pheromone increases citrus mealybug parasitism by Anagyrus sp. near pseudococci (Girault)

The present study was aimed at elucidating the role of lavandulyl senecioate (LS), the sex pheromone of Planococcus ficus, in host selection of the parasitoid Anagyrus sp. near pseudococci. Field trials were carried out in Portugal, Italy and Israel. The effect of LS on the parasitism rate of the wasp was determined by exposing sentinel mealybugs combined with pheromone dispensers impregnated with LS, in comparison with other baits: lavandulyl isovalerate (LI); planococcyl acetate (PAc); and unbaited control traps. In addition, in order to study the host location behavior of A. sp. near pseudococci, pheromone dispensers were placed at three different distances: inside the trap, 30 or 60 cm away from the trap. The number of parasitoid females inside the traps, the number of parasitized mealybugs, and the number of days required for the first parasitoid emergence were recorded. The response of A. sp. near pseudococci females to different doses of LS (25–1350 μg) was also evaluated using sticky plate traps. The rate of mealybug parasitism by A. sp. near pseudococci was significantly increased by LS in the three parasitoid populations. PAc and LI had no significant effect on the wasp parasitism rate in most of the trials. However, the Italian population of the parasitoid responded to PAc, showing apparently a different behavioral pattern. The number of parasitoid females trapped did not significantly differ between tested doses of LS. The use of LS as an arrestant in host location by the A. sp. near pseudococci female is discussed.     

Interspecific variation in the response to low temperature storage in different aphid parasitoids

Cold storage of natural enemies usually involves placing insects under constant subambient temperatures. Even at non-freezing temperatures, a reduction in survival is the norm. Using fluctuating thermal regimes (FTR) instead of constant low temperature (CLT) has shown that mortality due to accumulation of chilling injuries was significantly reduced in Aphidius colemani . Whether this phenomenon can be generalised to other parasitoid species is not known. The aim of this study was to analyse interspecific variation in the ability to tolerate cold storage under CLT (continuous 2°C) versus FTR (daily cycle: 2°C for 22 h and 20°C for 2 h) for various durations (0–20 days). Survival, sex ratio and development of five different Aphidiine parasitoids were analysed: A. colemani , Aphidius ervi , Aphidius matricariae , Ephedrus cerasicola and Praon volucre. A marked interspecific variation in the ability to tolerate cold storage was observed: A. matricariae and A. ervi were most chill tolerant, P. volucre and E. cerasicola had an intermediate chill sensitivity and A. colemani was most chill sensitive. In all species tested, FTR significantly reduced cold-induced mortality. This phenomenon was manifested more in chill-sensitive species as they probably accumulate chilling injuries more rapidly. The sex ratio remained unaffected in all the species. Interspecific variation was also observed in developmental responses to cold storage. Under CLT, time to adult emergence of A. matricariae, A. colemani, A. ervi and P. volucre was temporarily stopped and in E. cerasicola it increased. Under FTR, the short daily intervals at 20°C for 2 h allowed parasitoids to continue development in all the species. Interspecific differences are discussed. This study suggests that positive impact of FTR may apply to a wide range of species.