Aggressive interactions for a decentralized regulation of foraging activity in the social wasp Polistes versicolor

Physical aggression among nestmates is commonly observed in animal societies like Polistes paper wasps, where it can be used to suppress worker reproduction. There is no consensus about how individuals use aggression in contexts other than reproduction. In order to clarify this topic, the regulation of worker-foraging behavior was studied in the Neotropical eusocial wasp Polistes versicolor. By experimentally manipulating food demand, we found evidence that aggression is used as a decentralized mechanism of regulating foraging, because after food supplementation: (1) aggression levels and foraging rates decreased and (2) aggression received and exhibited by foragers and non-foragers decreased. P. versicolor can use aggression in both reproductive and foraging contexts. The conclusion is drawn that this species is a good model for understanding how individuals differ from aggression related to reproduction and foraging, which would allow understanding of the evolutionary shift in the function of aggression from being the mechanism of reproductive control to being co-opted for the decentralized, self-organized regulation of worker-foraging.     

Lipogenesis in an adult parasitic wasp

The goal of this study was to determine the extent of lipogenesis in the parasitoid Eupelmus vuilletti (Hymenoptera: Eupelmidae). Carbohydrate and lipid metabolism were followed in glucose-fed and starved females over 3 days. Fed females increased their glycogen level, while maintaining their lipid level. Starved females used most of their glycogen, while maintaining their lipid level too. Thus, females either use exclusively sugars to preserve their lipid reserves, or maintained a steady renewal of lipids through lipogenesis. The incorporation of radioactively marked glucose into lipids showed however that lipogenesis did not occur at a sufficient level to increase lipid reserves and to compensate for lipid use. This result has important implications for understanding nutrients allocation strategy in this species as the amount of lipids is almost totally fixed upon the emergence. From an evolutionary perspective, we call for detailed physiological studies of lipogenesis in a wide range of adult hymenopterans, as the absence of lipogenesis could be common to all of Aculatea.     

Lifetime gains of host-feeding in a synovigenic parasitic wasp

Abstract. Understanding behavioural decisions relative to host use for feeding or reproduction by foraging parasitoids requires not only the study of metabolic pathways followed by nutrients, but also the quantification of lifetime fitness gains of each alternative behaviour. By using a combination of observational and manipulative approaches, the lifetime host‐feeding gains are measured both in terms of fecundity and longevity in the parasitoid Eupelmus vuilletti. Host‐feeding increases both egg production and longevity. The increase in fecundity is mainly determined by the amount of lipids obtained whereas the lifespan extension is mainly determined by carbohydrates. Proteins obtained through host‐feeding have been implicated previously in egg production by parasitoids but protein intake has no effect on fecundity and longevity in E. vuilletti. The amount of nutrients gained through host‐feeding and invested in eggs is variable and changes over the lifetime of the animal. Therefore, lifetime feeding gains are best understood through the construction of dynamical budgets running over the entire lifespan of an insect.     

Male altruism and wing polymorphism in a parasitic wasp

Males ofTrichogramma sp., a gregarious parasitoid which attacks eggs of the yellow-legged tussock mothIvela auripes (Lepidoptera: Lymantriidae), are polymorphic for wings. In mating within host eggs, no difference in mating success was observed between winged (large) males and wingless (small) males, whereas in mating outside eggs, the former were superior to the latter. Some wingless males were observed to perform sneaking copulation on egg masses. In the 1-male brood, which is thought to be founded by 1 mother wasp, the male size tended to decrease as the number of females per brood increased. But in the 2-male brood, which is assumed to be added with 1 more smaller male produced by the second mother wasp in double parasitism, the larger male did not reduce his size, compared with the male of the 1-male brood with an equal number of females. This phenomenon can be explained reasonably by a version of the kin-selection theory: When there is only 1 male in a host egg, he transfers resources in the egg to his sister females, but, when another male appears, he decides to act to the females less altruistically.     

Genetic variation in sex allocation in a parasitic wasp: variation in sex pattern within sequences of oviposition

In order to maximize their fitness under Local Mate Competition (LMC), arrhenotokous female wasps have to produce a precise sex ratio when encountering hosts. Recent progress in the theory of hymenopterous parasitoid reproduction suggest that they manage to do it by laying male and female eggs in a particular order and that such reproductive strategies are adaptive. Therefore, the determinism of such sequential patterns would be regulated by genetic control on which natural selection could act. To test this hypothesis, sequences of oviposition were recorded in a set ofTrichogramma brassicae Bezdenko (Hymenoptera; Trichogrammatidae) females and in their daughters by providing themEphestia kuehniella Zeller (Lepidoptera; Pyralidae) eggs. In order to describe accurately sex pattern within these oviposition sequences, I present a joined non-parametric and multivariate statistical method. It is shown thatT. brassicae females do not produce male and female eggs in random sequences. Moreover, the way they organize the sequence of the sexes in their progeny seems to be under a strong genetic control. The evolutionary consequences of such results are discussed.     

Genetic variation in patch time allocation in a parasitic wasp

1. The intra-patch experience acquired by foraging parasitoid females has often been considered to have a strong influence on their tendency to leave a patch, and thus on their total patch residence time. Most studies that have been performed on this subject suggest that the patch-leaving rules observed are adaptive because they enable the females to adjust their patch residence time to local environmental conditions.
2. Considering a behavioural rule as being adaptive supposes that it has been progressively settled by natural selection, and thus that there is, in the population, genetic variation on which the natural selection could act.
3. Therefore, this study aimed to discover whether there was indeed genetic variability in the patch-leaving decision rules in a population of the egg parasitoid species Telenomus busseolae , which attacks patches of its hosts, the eggs of Sesamia nonagrioides . Different wasp families were compared using the isofemale lines method, and the behavioural records were analysed by means of a modified version of the Cox's proportional hazards model proposed by Haccou et al . (1991 ) and Hemerik, Driessen & Haccou (1993 ).
4. The results obtained show that T. busseolae females increase their tendency to leave the patch after each successful oviposition. Each host rejection also led to an increase in the tendency to leave the patch, but this effect was smaller when host rejections were observed between two ovipositions occurring in rapid succession. Subsequent visits to the patch also increased the patch-leaving tendency.
5. Genetic variability was found in both the global patch-leaving tendency and in the effect that successful ovipositions and host rejections have on this tendency.
6. The adaptive and evolutionary consequences of these results are discussed.     

Ambient temperature affects mechanosensory host location in a parasitic wasp

Certain parasitic wasps (Ichneumonidae, Pimplinae) use self-produced vibrations transmitted on plant substrate to locate their immobile concealed hosts (i.e. lepidopteran pupae). This mechanosensory mechanism, called the vibrational sounding, depends both on physical cues of the environment and physical activity of the parasitoid and is postulated to depend on ambient temperature. We analysed the influences of temperature on vibrational sounding by choice experiments using plant-stem models with hidden host mimics in the temperate species Pimpla turionellae. The results show a significant effect of temperature on host-location activity and on the success of this process. Outside an optimum range, the performance of the wasps decreased both at low and high temperatures. Below 10°C and beyond 24°C, the wasps displayed (1) substantial reduction in responsiveness, i.e. proportion of females showing ovipositor insertions, (2) reduction of quantitative activity with ovipositor insertions in the individuals, and (3) reduced precision of mechanosensory host location. Nevertheless, female wasps were able to locate their host over a surprisingly broad range of ambient temperatures which indicates that the wasps are able to compensate for temperature effects on vibrational sounding.     

A learning-related variation in electroantennogram responses of a parasitic wasp

ABSTRACT Odour responses of parasitic insects, in search of their hosts, can change due to experience. Leptopilina heterotoma (Thomson) (Hymenoptera; Eucoilidae), a parasitic wasp of drosophilid larvae, is known to alter its preference for odours emanating from host food substrates through learning. These kinds of behavioural modifications in insects are assumed to be the result of complex processes in the brain. The results presented in this report, however, suggest that this learning-related behavioural variation is not restricted to brain processes but that it involves changes in sensitivity of olfactory receptor neurones.     

Differential dispersal and female-biased sex allocation in a parasitic wasp

1. Differential dispersal of males and females from a population is predicted to result in biased sex-allocation decisions, even in the absence of sibmating.
2. Mated Bracon hebetor Say (Hymenoptera: Braconidae) females produce distinctly female-biased sex ratios (≈ 30% male), yet sibmating is not a feature of the mating biology of this species. Therefore the dispersal behaviour of male and female B. hebetor from caged subpopulations was examined.
3. A higher proportion of females than males dispersed from the caged subpopulations. Furthermore, females dispersed earlier than males. This suggests that the level of competition for mates experienced by males is higher than the level of competition for hosts experienced by sisters.
4. Roughly half of the dispersing females left after they had mated. Females generally mate once in their lifetimes, suggesting that competition between brothers for mates may be high.     

Constrained oviposition and female-biased sex allocation in a parasitic wasp

 In haplodiploid organisms such as parasitic wasps, substantial oviposition by females without sperm is predicted to cause mated females to bias their offspring sex ratios towards daughters. The effect of the production of sons by unmated and sperm-depleted (constrained) females on sex allocation by mated females was studied in two populations of the parasitic wasp Bracon hebetor over 3 years. B. hebetor females who depleted their sperm reserves from prior matings rarely remated and became constrained to produce only sons. Constrained females readily oviposited and produced clutches similar in size to those produced by mated females. Although the fraction of constrained females in the population varied considerably between sites and sampling dates, it was usually high enough to favor the production of female-biased sex ratios by mated females. Mated females consistently produced female-biased sex ratios. However, we found no evidence that the sex ratios produced by mated females from the field shifted in relation to the proportion of constrained females in the population. Females held with males or held in isolation also produced female-biased sex ratios. These findings suggest that, in B. hebetor, mated females produce sex ratios that reflect the average fraction of constrained females over evolutionary time. Received: 21 June 1996 / Accepted: 27 August 1996     

Characterization of a hymenoptaecin-like antimicrobial peptide in the parasitic wasp Nasonia vitripennis

Hymenoptaecin is a Hymenoptera insect-specific, glycine-rich antimicrobial peptide (AMP) found in non-parasitic bees. Here, we describe a unique hymenoptaecin-like gene (named nahymenoptaecin-1) in the parasitic wasp Nasonia vitripennis, which codes for a larger protein precursor with a carboxyl-terminal hymenoptaecin-like domain (HLD) similar to the bee hymenoptaecin. We recombinantly produced its full-length bioactive form as well as 1–33 and 34–98 fragments (named HLD-n and HLD-c, respectively). Recombinant HLD exhibited activity against Gram-negative and Gram-positive bacteria at micromolar concentrations. Compared to the full-length peptide, HLD-c possessed similar potency in inhibiting the growth of Stenotrophomonus but had a narrower antibacterial spectrum, whereas HLD-n only displayed weak effect on Stenotrophomonus, suggesting that HLD-n is a crucial determinant for bacterial target selectivity while HLD-c represents its active unit for the whole molecule. Circular dichroism analysis combined with ab initio structure prediction by Robetta indicated that HLD-n adopts a random coil conformation whereas glycine-rich HLD-c forms a loose β-sheet structure. Relative to bee hymenoptaecin, the upstream region of HLD contains two accurately repeated proline-rich AMP-like peptides instead of an acidic propeptide. Such difference could be a consequence of exon shuffling of autonomous modules after speciation.     

Inheritance of gynandromorphism in the parasitic wasp Nasonia vitripennis

The parasitic wasp Nasonia vitripennis has haplo-diploid sex determination. Males develop from unfertilized eggs and are haploid, whereas females develop from fertilized eggs and are diploid. Females and males can be easily distinguished by their morphology. A strain that produces individuals with both male and female features (gynandromorphs) is studied. We provide data on female/male patterning within and between individuals, on environmental effects influencing the occurrence of gynandromorphism, and on its pattern of inheritance. A clear anterior/posterior pattern of feminization is evident in gynandromorphic individuals that developed from unfertilized haploid eggs. The proportion of gynandromorphic individuals can be increased by exposing the mothers to high temperature and also by exposing embryos at early stages of development. Selection for increased gynandromorph frequency was successful. Backcross and introgression experiments showed that a combination of a nuclear and a heritable cytoplasmic component causes gynandromorphism. Analyses of reciprocal F(2) and F(3) progeny indicate a maternal effect locus (gyn1) that maps to chromosome IV. Coupled with previous studies, our results are consistent with a N. vitripennis sex determination involving a maternal/zygotic balance system and/or maternal imprinting. Genetics and temperature effects suggest a temperature-sensitive mutation of a maternally produced masculinizing product that acts during a critical period in early embryogenesis.     

Comparing different floral resources on the longevity of a parasitic wasp

1 The effects of floral resources of several important non‐crop host plants of Lygus lineolaris on the longevity of Anaphes iole, one of its natural enemies, was studied. 2 Median longevity of A. iole wasps provisioned with floral resources (Erigeron annuus, Oenothera speciosa, Lamium amplexicaule, and Capsella bursa‐pastoris) was in the range 1.27–3.24 days, and did not differ from wasps in the distilled water only control (1.46–2.81 days), but was less than median longevity of wasps provisioned with distilled water + sucrose (5.30–12.46 days). No difference in longevity was observed between gender, although females usually lived slightly longer than males. 3 High‐performance anion‐exchange chromatography analyses of O. speciosa floral nectar revealed that the major carbohydrate components were sucrose, glucose, and fructose. 4 The results indicate that the floral resources of some non‐crop plants that serve as important reproductive hosts for L. lineolaris offer little or no benefit to A. iole.     

Rate of nutrient allocation to egg production in a parasitic wasp

Recent years have seen a marked increase in our awareness of the need to incorporate greater physiological realism into studies of parasitoid behaviour and population dynamics. Quantification of the number of eggs produced as a result of a host-feeding event, the host-feeding gain, is essential for predicting when a parasitoid should bypass an opportunity for current reproduction (i.e. laying eggs) in order to feed from the host and, thus, increase its chances for future reproduction (i.e. producing further eggs). Using radioactively labelled amino acids, one of the main constituents of insect haemolymph, we followed the incorporation of a known quantity of nutrients into each individual egg laid over a long period of time relative to the average life span of the parasitoid. Although the maximum incorporation of nutrients obtained by the female from a discrete feeding event occurs within a short period of time, a large proportion of nutrients are stored and used gradually for egg production throughout the life of the parasitoid. We therefore provide novel experimental evidence showing that feeding gain is not a discrete event in time occurring shortly after feeding, as has so far been assumed, but is instead spread throughout the parasitoid''s lifetime. This has important consequences for calculating the increase in lifetime fitness as a result of a feeding event, a common currency of models that aim to predict feeding and oviposition behaviour in parasitoids.     

Comparative activity pattern during foraging of four albatross species

The activity patterns of foraging Yellow‐nosed Diomedea chlororhynchos, Sooty Phoebetria fusca, Black‐browed D. melanophris impavida and Grey‐headed Albatross D. chrysostoma were compared using loggers recording the timing of landing and take‐offs, as well as the duration of bouts in flight or on the water, and the overall time spent in flight. The four species spent a similar proportion of their foraging time in flight (56–65%). During the day they were mostly flying (77–85% of the daylight period) whereas at night they were mainly (61–71%) sitting on the water. The amount of time spent in flight during the daytime foraging period was related to the amount of time spent sitting on the water at night. Differences between species occurred in the duration of bouts in flight and on the water as well as in the frequency of landings and in the time elapsed between successive landings. Yellow‐nosed Albatrosses were more active than the other species, with more frequent short bouts in flight and more frequent successive landings at short intervals. Sooty Albatrosses landed or took‐off less often than the other species and were more active just before dusk. Black‐browed and Grey‐headed Albatrosses were more active at night, especially the first part of the night and far from the colonies. Their trips consisted of a commuting part and a foraging part. Black‐browed Albatrosses landed more often during the foraging than the commuting part, suggesting that they were not searching when travelling. The study suggests that there is no fundamental difference between the overall activity budgets of the four species although they show distinctive diet, morphology and life history traits. The differences observed between the four species were related mainly to differences in foraging technique. Comparison with the Wandering Albatross, the only species for which data were available previously, suggest that this larger species might differ completely in foraging technique from the smaller albatrosses.     

Food conversion efficiency of a parasitic wasp, Nemeritis canescens

Abstract. 1. The calorific efficiency with which N. canescens converts the larva of E. kuehniella into its own tissues has been measured by microbomb calorimetry.
2. The calorific values found for Ephestia larvae are high in comparison with those of other insects and may be associated with their high fat content.
3. The growth efficiency of 61% achieved by Nemeritis is sustained by the higher assimilation efficiency of 94%, owing to the parasitoid's habit of feeding directly on the host's haemolymph.
4. The overall efficiency of conversion of adult moth (host) to adult ichneumonid (parasitoid) is of the order of 59% which is broadly representative of endoparasitoids and higher than that achieved by true predators.     

Kairomone mediated host-finding behavior in the parasitic wasp Orgilus lepidus

Host-finding by the parasitic wasp Orgilus lepidus, a braconid parasite, is mediated by two kairomones present in the frass of the host insect, the potato tuberworm. A volatile substance identified as heptanoic acid elicits heightened searching behavior, resulting in the parasite contacting the frass. A contact chemical stimulus in the frass induces the parasite to probe the substrate with the ovipositor, culminating in contact with the host.

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Zusammenfassung Das Auffinden des Wirts durch die parasitische Wespe Orgilus lepidus wird durch zwei Kairomone vermittelt, die im Bohrmehl des Wirtsinsekts, der Kartoffelmotte (Phthorimaea operculella) vorliegen. Eine flüchtige Substanz, identifiziert als Heptansäure, löst erhöltes Suchverhalten aus, das zur Kontaktnahme des Parasiten mit dem Bohrmehl führt. Ein chemischer Kontaktreiz im Bohrmehl veranlasst den Parasiten, das Substrat mit dem Legestachel solange zu sondieren, bis er mit dem Wirt in Berührung kommt.