Does Manipulation by the Parasitoid Wasp Cotesia glomerata (L.) Cause Attachment Behaviour of Host Caterpillars on Cocoon Clusters?

Some parasitoid wasps appear to control the behaviour of their hosts. However, altered behaviours of parasitised hosts are not necessarily caused by parasitoids but are sometimes the result of traumatic side effects of parasitism. However, it was difficult for us to discriminate the cause of host's behaviours between manipulation by parasitoids and traumatic side effects. Larvae of the parasitoid wasp Cotesia glomerata form cocoon clusters after egression from the parasitised host caterpillar Pieris brassicae . Following parasitoid egression, host caterpillars survive for several days and remain near the cocoon clusters. These caterpillars may repel solitary pteromalid hyperparasitoid wasps, Trichomalopsis apanteloctena , that attempt to parasitise fresh C. glomerata pupae. We allowed hyperparasitoids to attack cocoon clusters in the field and laboratory and then assessed the costs and benefits to C. glomerata of attachment by the parasitised caterpillars. The eclosion success of C. glomerata in cocoon clusters with attached caterpillars was higher than that in clusters without attached caterpillars in both field and laboratory experiments. This difference was attributed to shorter hyperparasitoid visits to cocoon clusters with attached host caterpillars. However, large cluster size was potentially costly for host attachment, because the duration of host caterpillar attachment decreased with increasing numbers of C. glomerata per caterpillar. This trade-off may be related to shortages of fat body resources, which are shared between the development of wasp larvae and the survival of host caterpillars. Therefore, we concluded that caterpillar attachment satisfied some requirements of host manipulation by C. glomerata .     

Host behaviour manipulation as an evolutionary route towards attenuation of parasitoid virulence

By definition, insect parasitoids kill their host during their development. Data are presented showing that ladybirds not only can survive parasitism by Dinocampus coccinellae, but also can retain their capacity to reproduce following parasitoid emergence. We hypothesize that host behaviour manipulation constitutes a preadaptation leading to the attenuation of parasitoid virulence. Following larval development, the parasitoid egresses from the host and spins a cocoon between the ladybird's legs. Throughout parasitoid pupation, the manipulated host acts as a bodyguard to protect the parasitoid cocoon from predation. The parasitoid has evolved mechanisms to avoid killing the host prematurely so that its own survival is not compromised. Bodyguard manipulation may thus constitute a selective trait for the evolution of true parasitism in some host–parasitoid associations.     

The cost of a bodyguard

Host manipulation by parasites not only captures the imagination but has important epidemiological implications. The conventional view is that parasites face a trade-off between the benefits of host manipulation and their costs to fitness-related traits, such as longevity and fecundity. However, this trade-off hypothesis remains to be tested. Dinocampus coccinellae is a common parasitic wasp of the spotted lady beetle Coleomegilla maculata. Females deposit a single egg in the haemocoel of the host, and during larval development the parasitoid feeds on host tissues. At the prepupal stage, the parasitoid egresses from its host by forcing its way through the coccinellid's abdominal segments and begins spinning a cocoon between the ladybird's legs. Remarkably, D. coccinellae does not kill its host during its development, an atypical feature for parasitoids. We first showed under laboratory conditions that parasitoid cocoons that were attended by a living and manipulated ladybird suffered less predation than did cocoons alone or cocoons under dead ladybirds. We then demonstrated that the length of the manipulation period is negatively correlated with parasitoid fecundity but not with longevity. In addition to documenting an original case of bodyguard manipulation, our study provides the first evidence of a cost required for manipulating host behaviour.     

Avoidance of the host immune response by a generalist parasitoid, Compsilura concinnata Meigen

Abstract.  1. Ecological interactions between parasitoids and their hosts are extremely strong as parasitoid offspring rely entirely on an individual host to complete development. The ability of a parasitoid to use a host is influenced directly by the degree to which the parasitoid can overcome host defences and grow within the host.
2. Hymenopteran parasitoids have evolved different host-specific strategies to defeat the host immune system, such as the use of venom, endosymbiont virus, or mimicking the host tissue. Dipteran parasitoids from the Tachinidae family do not use these subterfuges and rely mainly on avoiding the host immune system by hiding in specific tissues.
3. Little is known of the effect of this strategy on the host immune system, the absorption of nutrients by the parasitoid larvae, or the implications for parasitoid host range.
4. In this study, the impact of a polyphagous tachinid parasitoid Compsilura concinnata Meigen on a pest lepidopteran Trichoplusia ni Hübner are assessed. Phenoloxidase levels and haemolymph proteins were measured in parasitised T. ni as a function of host immune response.
5. Haemolymph phenoloxidase in the host did not vary with parasitisation but was triggered when a piece of monofilament was implanted in the haemocoel. Haemolymph proteins were depleted in heavily parasitised T. ni .
6. These results indicate that C. concinnata has a strategy that avoids the host immune system, and accesses the necessary nutrients for larval growth. This strategy could explain the success of this tachinid and its wide host range.     

Host behavior modification of Achaearanea tingo (Araneae: Theridiidae) induced by the parasitoid wasp Zatypota alborhombarta (Hymenoptera: Ichneumonidae)

Behavioral manipulation involving Zatypota (Ichneumonidae: Pimplinae) parasitoids and their spider hosts is usually associated with an increase in web complexity at the location where the parasitoid larva builds its cocoon. A higher number of web threads at this location may improve stability and provide a physical barrier against potential predators. However, we observed that parasitized individuals of Achaearanea tingo attacked by Z. alborhombarta change the three‐dimensional structure of their webs to a very simple and strong structure composed of two cables attached to the surrounding vegetation. This structure holds the curled leaf formerly used by the spider as a shelter. The parasitoid larva remains protected within this shelter after killing the host. The architectural pattern of the cocoon webs of A. tingo indicates that host manipulation is characterized by the repetition of one specific subroutine involved in web construction. Similar alterations have been previously described for cocoon webs constructed by parasitized orb‐weavers, but not for the three‐dimensional webs of theridiids.     

Remarkable similarity in body mass of a secondary hyperparasitoid Lysibia nana and its primary parasitoid host Cotesia glomerata emerging from cocoons of comparable size

Lysibia nana is a solitary, secondary idiobiont hyperparasitoid that attacks newly cocooned pre-pupae and pupae of several closely related gregarious endoparasitoids in the genus Cotesia, including C. glomerata. Prior to oviposition, the female wasp injects paralysing venom into the host, thus preventing further development. Here, host fate, emerging hyperparasitoid mass, and egg-to-adult development time was compared in hosts parasitized at different ages over 24-h intervals. Cocoons of C. glomerata were parasitized by L. nana at 12, 36, 60, 84, and 108 h post-egression from the secondary host, Pieris brassicae. Hyperparasitoid survival exceeded 80% in hosts parasitized within the first 60 h after pupation, but dropped thereafter, with no hyperparasitoids emerging in hosts aged 108 h. The mass of hyperparasitoids was positively correlated with the mass of the host cocoon, and this relationship remained consistent in hosts up to 60 h old. Within each host age cohort, the mass of male and female wasps was not significantly different. Development time in L. nana was uniform in hosts up to 60 h old, but increased significantly in 84-h-old hosts, and male wasps completed their development earlier than female wasps. Regulation of host growth varied with the age of the host at parasitism, with the early growth of older hosts reduced much more dramatically than young hosts. Unlike most parasitoids, pupal hyperparasitoids do not make cocoons but instead pupate within the already prepared cocoon of the host parasitoid. Consequently, for a given mass of cocoon, newly emerged L. nana adults were remarkably similar in size with male and female adults of C. glomerata. This reveals that L. nana is extremely efficient at exploiting its primary parasitoid host.     

Effects of parasitization of Trichoplusia ni by Chelonus sp.

ABSTRACT. Parasitization of Trichoplusia ni (Huebner) (Lepidoptera: Noctuidae) by Chelonus sp. (Hymenoptera: Braconidae), an egg-larval parasitoid, leads to precocious cocoon spinning of the host in the fourth (penultimate) stadium followed by parasitoid emergence from the prepupa. We have investigated the mechanism by which Chelonus sp. disrupts host development. The developing larva and fluids injected by the adult female separately from the egg, are not the source of these effects, but it remains a possibility that the teratocytes, originating from the trophamnion of the parasitoid egg, are responsible. The titre of the juvenile hormone esterase activity in the haemolymph of the parasitized fourth instar host is similar to that in the initial period of the final instar of normal T. ni, but lacks the postwandering peak of activity. The increased JHE activity leads to a reduced JH titre early in the fourth stadia. This indicates that disruption of host development occurs within 12h after apolysis to the fourth stadium, if not before. Anti-juvenile hormone activity is not detected in extracts of parasitized T. ni. The morphological and behavioural changes associated with precocious development of the T. ni host are prevented by applications of juvenile hormone I, juvenile hormone II and the juvenoid, Ro 10–3108, but not juvenile hormone III and the juvenoid R 20458. However, these applications fail to prevent the onset of juvenile hormone esterase activity, another marker of precocious development. These observations indicate that simple anti-juvenile hormone activity may not be the mechanism of disruption of host development. Development of the parasitoid is disrupted by application of Ro 10–3108 and juvenile hormones I, II and III, but timing of eclosion is only affected by application of juvenile hormone I, juvenile hormone II and Ro 10–3108. This observation may indicate a discrimination by the parasitoid between its own juvenile hormone III and the host's juvenile hormone II.     

The effects of host weight at parasitism on fitness correlates of the gregarious koinobiont parasitoid Microplitis tristis and consequences for food consumption by its host, Hadena bicruris

Gregarious koinobiont parasitoids attacking a range of host sizes have evolved several mechanisms to adapt to variable host resources, including the regulation of host growth, flexibility in larval development rate, and adjustment of clutch size. We investigated whether the first two mechanisms are involved in responses of the specialist gregarious parasitoid Microplitis tristis Nees (Hymenoptera: Braconidae) to differences in the larval weight and parasitoid load of its host Hadena bicruris Hufn. (Lepidoptera: Noctuidae). In addition, we examined the effects of parasitism on food consumption by the host. Parasitoids were offered caterpillars of different weight from all five instars, and parasitoid fitness correlates, including survival, development time, and cocoon weight, were recorded. Furthermore, several host growth parameters and food consumption of parasitized and unparasitized hosts were measured. Our results show that M. tristis responds to different host weights by regulating host growth and by adjusting larval development rate. In hosts with small weights, development time was increased, but the increase was insufficient to prevent a reduction in cocoon weight, and as a result parasitoids experienced a lower chance of successful eclosion. Cocoon weight was negatively affected by parasitoid load, even though host growth was positively affected by parasitoid load, especially in hosts with small weights. Later instars were more optimal for growth and development of M. tristis than early instars, which might reflect an adaptation to the life‐history of the host, whose early instars are usually concealed and inaccessible for parasitism on its food plant, Silene latifolia Krause (Caryophyllaceae). Parasitism by M. tristis greatly reduced total host food consumption for all instar stages. Whether plants can benefit directly from the attraction of gregarious koinobiont parasitoids of their herbivores is a subject of current debate. Our results indicate that, in this system, the attraction of a gregarious koinobiont parasitoid can directly benefit the plant by reducing the number of seeds destroyed by the herbivore.     

Regulation of host diapause by an insect parasitoid

Abstract. 1. The interaction between larval development and parasitism by the braconid wasp Cotesia koebelei (Riley), was investigated in a population of the butterfly Euphydryas editha (Boisduval) (Nymphalidae). In this population, the butterfly host has an obligatory overwintering larval diapause.
2. It was found that E. editha larvae harbouring parasitoids were more likely to pass through an extra feeding instar before entering diapause than were non-parasitized conspecifics.
3. In addition, some individuals that were experimentally exposed to multiple parasitoid attacks bypassed diapause completely; these larvae passed through five or six feeding instars, reaching sizes typical of final instar post-diapause larvae.
4. The observed effect of superparasitism occurred regardless of whether the host larvae subsequently produced mature parasitoids, suggesting that parasitoid attack is sufficient to invoke the response.
5. It is proposed that the parasitoid C.koebelei regulates the number of pre-diapause feeding instars of its insect host E. editha, and that some component of the female venom, injected at oviposition, is responsible for this regulation.     

Sex ratio regulation in Coccygomimus turionella Linnaeus (Hymenoptera: Ichneumonidae) and its ecological implications

Abstract. 1. Sex regulation and its relevance to the ecology of a k-selected pupal parasitoid was investigated in Coccygomimus turionellae.
2. The ratio varied with host size, females predominating in large hosts.
3. Egg transfer experiments and comparative mortality rates among the progeny of virgin and inseminated females demonstrated that the phenomenon was due to parental behaviour.
4. The study of the mechanism confirmed Aubert's hypothesis of host size estimation with the addition that the host had to be exposed from the poles and had to contain the proper host kairomones.
5. Host size was highly correlated to parasitoid fecundity via influences on size and longevity but not the number of ovarioles per female or daily egg production.
6. Host encounters are more limiting than egg production and host size had no effect on host acceptance.
7. Sex regulation allows a maximal host encounter rate at the same time that it maximizes the reproductive potential of female progeny.
8. Low host density increased the production of female progeny resulting in more offspring searching for the limited resource. Concealed hosts and a high host density resulted in a shift towards a Fisher 1:1 sex ratio.     

Parasitoid genus‐specific manipulation of orb‐web host spiders (Araneae,Araneidae)

相似文献   

Effects of Helicoverpa armigera (Noctuidae, Lepidoptera) host stages on some developmental parameters of the uniparental endoparasitoid Meteorus pulchricornis (Braconidae, Hymenoptera)

A single choice test was performed to examine developmental strategies in the uniparental endoparasitoid Meteorus pulchricornis and its host, the cotton bollworm Helicoverpa armigera. The results support the dome-shaped model in which the fitness functions are 'dome-shaped' relative to size (and age) of host at parasitism. Older and, hence, larger host larvae were simply not better hosts for the developing parasitoids. Although parasitoid size (measured as cocoon weight and adult hind tibia length) was positively correlated with host instars at parasitism, parasitoids developing in larger hosts (L5 and L6) suffered much higher mortality than conspecifics developing in smaller hosts (L2-L4). Furthermore, egg-to-adult development time in M. pulchricornis was significantly longer in older host larvae (L4-L6) than in the younger. Performance of M. pulchricornis, as indicated by fitness-related traits, strongly suggests that the L3 host is the most suitable for survival, growth and development of the parasitoid, followed by both L2 and L4 hosts; whereas, L1, L5 and L6 are the least favourable hosts. The oviposition tendency of M. pulchricornis, represented by parasitism level, was not perfectly consistent with the performance of the offspring; L2-L4 hosts, although with the same parasitism level, had offspring parasitoids with differences in fitness-related performance. Larval development in Helicoverpa armigera was usually suspended, but occasionally advanced, in the final instar.     

Development of the solitary endoparasitoid Microplitis demolitor: host quality does not increase with host age and size

Abstract.  1. Many studies examining the relationship between host size, an index of host quality, and parasitoid fitness use development time and/or adult parasitoid size as currencies of fitness, while ignoring pre-adult mortality. Because the physiological suitability of the host may vary in different stages, sizes, or ages of hosts, a misleading picture of host quality may therefore be obtained in cases where fitness is based on only one or two developmental traits.
2. The development of the solitary koinobiont endoparasitoid Microplitis demolitor is examined in different larval age-classes of its host the soybean looper Pseudoplusia includens . Hosts were parasitised on days 1–8 after hatching from the egg, and development time, adult body size, and mortality of the parasitoid were compared.
3. A comparison of larval growth trajectories (using dry body mass) of M. demolitor revealed that parasitoid larvae attained over twice as much body mass in old hosts than in younger hosts. Similarly, adult parasitoid size at eclosion generally increased with host size, although parasitoids developing in smaller hosts lost a much lower proportion of mass between pupation and eclosion.
4. Overall egg-to-adult development was most rapid in intermediate-aged hosts, and longer in hosts at opposite ends of the age continuum. Moreover, parasitoid mortality varied non-linearly with host stage, and was generally higher in very young and older hosts.
5. Based on these results and other empirical data for koinobionts, it is argued that fitness functions in this group of parasitoids are not simply a positive function of host size or age, but instead may be distinctly dome-shaped, both patterns reflecting the degree of physiological and nutritional compatibility between the two organisms.     

Factors affecting the rate of attack by Cotesia rubecula (Hymenoptera: Braconidae)

Abstract. 1. The relationship between responses of the insect parasitoid Cotesia rubecula (Marshall) to kairomones produced by the feeding activities of its host, Pieris rapae (L.), and patterns of parasitism were investigated under field conditions.
2. Parasitoid adults aggregated in patches with the highest densities of host larvae but there was no commensurate increase in the rate of attack in these patches.
3. The rate of attack was not limited by the availability of eggs.
4. The rate of parasitoid attack was highest where feeding damage by the host was highest, irrespective of current host density.
5. The rate of parasitoid attack was further influenced by host age distribution. Late instar larvae were less susceptible to parasitism than were early instar larvae. The rate of attack on early instar larvae occupying the same plants as late instar larvae was reduced. This reduction in rate of attack was due to limitations on parasitoid search time imposed by the increased feeding damage associated with large host larvae and by the increased time the parasitoid required to recover from an attack on these large host larvae.     

Communication of leaf suitability by gregarious eastern tent caterpillars (Malacosoma americanum)

ABSTRACT. 1. Previous work has shown that leaf age affects recruitment trail marking by eastern tent caterpillars ( Malacosoma americanum Fabr.). Young leaves of host plants elicit trail marking to a greater degree than mature leaves.
2. Experiments were conducted to establish the relationship between the differential behavioural responses of larvae to young and mature leaves and the suitability of foliage for larval growth and survival. Foliage of black cherry ( Prunus serotina Ehrh.), a typical rosaceous host plant, was used for this comparison.
3. Larvae preferred young leaves to mature leaves in choice tests, and marked more to young leaves than to mature leaves in no-choice tests.
4. Mature leaves supported adequate growth through two larval instars of rearing, but thereafter were unsuitable for growth. Larvae fed mature leaves had lower pupal weight, poorer survival, and grew less efficiently than larvae fed young leaves.
5. The results support the hypothesis that the trail communication system of eastern tent caterpillars is an adaptation to efficiently locate leaves which are favourable for larval growth and survival.     

Behavioral manipulation of host caterpillars by the primary parasitoid wasp Cotesia glomerata (L.) to construct defensive webs against hyperparasitism

Many parasitoids control the behavior of their hosts to achieve more preferable conditions. Decreasing predation pressure is a main aim of host manipulation. Some parasitoids control host behavior to escape from their enemies, whereas others manipulate hosts into constructing defensive structures as barriers against hyperparasitism. Larvae of the parasitoid wasp Cotesia glomerata form cocoon clusters after egression from the parasitized host caterpillar of the butterfly Pieris brassicae. After the egression of parasitoids, the perforated host caterpillar lives for a short period and constructs a silk web that covers the cocoon cluster. We examined whether these silk webs protect C. glomerata cocoons against the hyperparasitoid wasp Trichomalopsis apanteroctena. In cocoon clusters that were not covered by silk webs (bare clusters), only cocoons hidden beneath others avoided hyperparasitism. In covered cocoon clusters, both cocoons hidden beneath others and those with a space between them and the silk web avoided hyperparasitism, whereas cocoons that contacted the silk webs were parasitized. The frequency of cocoons that were hidden beneath others increased with the increasing number of cocoons in a cluster, but the defensive effect of cluster size was thought to be lower than that of silk webs. However, the rate of hyperparasitism did not differ between covered and bare clusters when we allowed the hyperparasitoids to attack the cocoon clusters in an experimental arena. This result was thought to have been caused by low oviposition frequency by these hyperparasitoids. As a result, silk webs did not guard the cocoons from hyperparasitoids in our experiments, but would protect cocoons under high hyperparasitism pressure by forming a space through which the ovipositors could not reach the cocoons.     

Patch departure mechanisms and optimal host exploitation in an insect parasitoid

1. Patch-leaving decisions are of utmost importance in determining parasitoid foraging success. Parasitoids are known to use both marks left by hosts (chemical or otherwise) and ovipositions to assess host availability and to decide when to leave a host patch.
2. Previous studies have shown that, depending on the species, ovipositions either increase (an incremental mechanism) or decrease (a decremental mechanism) the patch residence times of parasitoids. Reports in the literature conflict on which mechanism is used by Venturia canescens , a parasitoid of pyralid moth larvae.
3. We hypothesize that, as a consequence of saturation in the capacity of the parasitoid to discriminate between host densities at high host numbers, V. canescens uses a decremental mechanism at low host numbers and an incremental one at high host numbers. We call this a 'switching mechanism'.
4. Our experiments show that even if discrimination capacity saturates, V. canescens uses a decremental mechanism over a wide range of host densities.
5. The distribution of hosts in different fruits species under field conditions suggests a switching mechanism would not evolve in natural situations.
6. A model of patch departure in V. canescens is constructed and tested using an independent set of experiments. The model suggests that the patch leaving mechanism in V. canescens is a stochastic decremental one. As might be expected from Weber's Law, the initial leaving tendency is a convex decreasing function of kairomone concentration. The leaving tendency increases exponentially with the time spent in the patch without ovipositing. Ovipositions cause a sudden increase in leaving tendency.
7. Simulations suggest that a decremental mechanism would be out-competed by either one indifferent to ovipositions or an incremental one, only when travel times are much larger than those that are likely to occur in the field.     

Development of a gregarious ectoparasitoid, Euplectrus separatae (Hymenoptera; Hymenoptera: Eulophidae), that parasitizes Pseudaletia separata (Lepidoptera: Noctuidae)

Euplectrus separatae is a gregarious ectoparasitoid that parasitizes Pseudaletia separata during its third to sixth (last) instars. The eggs of the parasitoid are fixed on the integument of the host dorsolaterally with a hard substance like a piling driven into the integument by the female wasp at the time of oviposition. The first instar of the parasitoid, which hatches three days after oviposition is nourished by ingesting the hemolymph of the host, and ecdyses to the second stadium six days after oviposition. Many hemocytes and epidermal cells were found assembled under the piling and places where a parasitoid had attached its mouth, suggesting that the host had repaired the integument destroyed by the parasitoid. Botryoidal tissue, which stained well with hematoxylin, began to develop from four days after oviposition and became gradually larger with development. Botryoidal tissue appears to function as a secretory organ for thread and a storage organ for nutrients. Seven days after oviposition, the parasitoid larvae migrate down from the dorsal surface to the ventral side of the host. Just before descending they ecdyse to the third stadium and kill the host during their migration. If all parasitoid larvae were removed artificially from the host before they migrate, the host did not die. However, removing the parasitoids after they had started to migrate did not prevent the death of the host. Transmission electron microscopic (TEM) observation of salivary glands of a parasitoid larva before migrating revealed that the salivary gland was composed of cells that were rich in rough surfaced endoplasmic reticulum (rough-ER) with many ribosomes and cells that were filled with a lot of vacuoles just before their collapse. After moving from the host body, the parasitoid larvae doubled in weight by ingesting the tissue of the host and then spun a cocoon. Almost all host tissues were consumed for growth of the parasitoid, like an idiobiont parasitoid.     

Intrinsic, inter-specific competition between egg, egg–larval, and larval parasitoids of plusiine loopers

Abstract.  1. Intrinsic, inter-specific competition between parasitoid wasp species is a key factor in ecological community dynamics and is particularly important for application in biological control. Here three parasitoid wasp species with overlapping host ranges and differing life history strategies were chosen to examine parasitoid–parasitoid interactions: the egg parasitoid Trichogramma pretiosum, the egg–larval, polyembryonic parasitoid wasp Copidosoma floridanum, and the gregarious larval parasitoid Glyptapanteles pallipes , with the plusiine loopers Acanthoplusia agnata and Trichoplusia ni as hosts.
2.  Copidosoma floridanum has been shown to be an intrinsically superior competitor against larval parasitoids because of their production and increased investment in a soldier larval caste during development, but little is known of their interactions with egg parasitoid species. Trichogramma pretiosum completely dominated intrinsic competition with C. floridanum regardless of oviposition order or sex of the C. floridanum egg.
3. Competition between C. floridanum and G. pallipes , however, depended on the host stage at which parasitism occurred, the sex of the C. floridanum egg, and parasitoid development time. Copidosoma floridanum outcompeted G. pallipes overall, despite the fact that G. pallipes injects a polyDNA virus into the host.
4. The sex of the C. floridanum egg was a significant factor in its ability to shift caste ratios to produce more soldiers in response to G. pallipes competition.
5. Only developing female C. floridanum responded to competition with G. pallipes by increasing the ratio of soldier to reproductive larvae, and this happened only when multiparasitism occurred in the host's 1st and 2nd instar.     

Limited scope for maternal effects in aphid defence against parasitoids

Abstract.  1. A mother's environment frequently affects her offspring's phenotype. Such maternal effects may be adaptive, in particular with respect to pathogens or parasites, for example if maternal exposure increases offspring resistance.
2. In aphids, maternal effects are likely to occur as a result of their telescoping generations. This study investigated whether maternal effects influence the susceptibility of the peach-potato aphid, Myzus persicae (Sulzer) (Hemiptera: Aphididae), to its parasitoid Diaeretiella rapae (M'Intosh) (Hymenoptera: Braconidae: Aphidiinae).
3. In a first experiment, susceptibility was compared among offspring of aphid mothers that had either no contact to parasitoids, had contact but were not attacked, or were attacked but not mummified. Mothers from the last group had successfully resisted the parasitoid.
4. In a second experiment using two different clones, maternal and progeny environment were manipulated by rearing each generation either on a benign (radish) or a more stressful host plant (silver beet) before progeny exposure to parasitoids.
5. The first experiment revealed no significant effect of the maternal treatment on offspring susceptibility to parasitoids and thus no evidence for trans-generational defence. In the second experiment, maternal environment effects were also weak, yet with a trend towards less susceptible offspring of aphid mothers reared on the more stressful plant. However, there was a significant difference among clones and a strong clone × progeny host plant interaction, illustrating that the outcome of a parasitoid attack may be determined by a complex interplay of genetic and environmental factors.
6. Overall, the results suggest that there is limited scope for maternal effects in aphid defence against parasitoids.