The fate of an internal parasitoid,Nemeritis canescens,in a variety of insects

• 1 The fate of Nemeritis canescens has been studied in 36 species or, counting different stages, in 51 kinds of insects, in order to discover the causes of its success or failure in each.
• 2 The parasitoid was able to develop to the adult stage in 14 of the species studied.
• 3 A defence reaction of the host, cellular encapsulation, was by far the most frequent cause of the death of canescens in species in which it could not develop.
• 4 Deposition of melanin over its mouth probably caused the death of canescens in two species; in other species the role of melanisation was subordinate to encapsulation.
• 5 Very few species, if any, were unsuitable as food; larvae of the parasitoid ingested and assimilated the blood of a wide variety of insects.
• 6 Some individuals of a few species were unsuitable as a habitat for the parasitoid larva.
• 7 The survival of canescens in suitable hosts is discussed with reference to the means by which this parasitoid resists defence reactions.
• 8 Attention is drawn to incidental results of the research: (i) a state of diapause in some hosts was transmitted to first-instar larvae of canescens and delayed their development; (ii) evidence was found that the teratocytes formed by braconid parasitoids function as a means of preventing cellular defence reactions, that they act by attrition of the host, and that they protect a larva of canescens present in the same host; (iii) observations concerning the behaviour of adult canescens in attacking some species, and the survival of supernumerary larvae after competing for the host, are mentioned.

     

Arrestment responses of the parasitoid, Nemeritis canescens, to a contact chemical produced by its host, Plodia interpunctella

ABSTRACT. The locomotory response of walking parasitoids to a contact chemical from their host is reviewed, and in particular the response of the ichneumonid, Nemeritis canescens Grav., to the mandibular gland secretion of its host, Plodia interpunctella Hubn., is investigated. In response to the presentation of the host chemical on a surface, a walking Nemeritis exhibits a complex ortho-kinetic response involving stopping, walking at a reduced speed and probing with the ovipositor. In response to the removal of the chemical following presentation, as would occur when the insect left the edge of the chemical patch, the wasp exhibits a klinotactic response which directs it back to the patch at an average angle of 157° relative to the orientation at the moment of stimulation. This turning-back response at the patch edge greatly increases the time spent on a patch of contact chemical. The waning of this response determines when a host patch is abandoned. This waning is retarded by increasing the concentration of contact chemical on the patch and by opposition while on the patch.     

The hosts of Nemeritis canescens a problem in the host specificity of insect parasitoids

• 1 Published records of the hosts of N.canescens have been collected and critically examined.
• 2 It is accepted that canescens has developed on twenty-three species; on one of them perhaps accidentally, on two with some doubt.
• 3 Twelve species were parasitized in nature; nine species in the laboratory. Two species served as hosts when artificially infected.
• 4 The natural hosts belong in the Pyralidae, Tinaeidae and Yponomeutidae; the laboratory hosts in the Pyralidae, Oecophoridae and Gelechiidae. One individual was reared from a Tortricid, perhaps accidentally.
• 5 The host specificity of N.canescens is not easily explained on either a systematic or an ecological basis. It offers interesting problems for research.

     

Food conversion efficiency by fleshfly larvae, Sarcophaga bullata

ABSTRACT. The efficiency of the conversion of the digested food (ECD) (liver) during the growing period of the larva of Sarcophaga bullata was determined. The values for ECD in four different determinations were 67.8, 69.1, 64.1 and 63.4%. These values are of the same order as ECD determined for some phytophagous caterpillars under the best conditions of food utilization, and seem to represent the highest values obtainable in a multicellular organism. It is concluded that such high efficiency rates have as prerequisites: fast growth in the larvae; and in the food, easy availability, ingestibility, and digestibility, high nutritional value, and reasonably high water content. Bacterial decomposition of the food during the test period appeared scarcely to influence the apparent ECD.     

The temporal effects of Dufour's gland secretion in host discrimination by Nemeritis canescens

Behavioural experiments with Nemeritis canescens Grav. have demonstrated that the secretions from its Dufour's gland are used as a marker pheromone which can affect the behaviour of other wasps towards host caterpillars bearing it. The external marker is produced within the complex of secretions from the Dufour's gland and has oviposition deterrent effect which lasts approximately 32 h after deposition.The sequence of behaviour patterns shown by individual Nemeritis is described and shows a significant increase in escape and avoidance reactions towards Ephestia caterpillars treated topically with the Dufour's gland contents.This paper presents evidence for the first time to indicate that Nemeritis reacts to an external marker as well as to an internal one. Similar behaviour towards filter paper treated topically with contents of whole Dufour's gland and its component heneicosane contribute evidence for the conclusion that the gland contents influence the wasp's behaviour and hence its avoidance of superparasitism of its host.

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Effets temporels de la sécrétion de la glande de Dufour sur la sélection des hôtes par Nemeritis canescens grav

Résumé Des expériences sur le comportement de N. canescens ont montré que les sécrétions de la glande de Dufour sont utilisées comme phéromone de marquage pouvant affecter le comportement des autres hyménoptères face aux chenilles contaminées. Ce maqueur externe est produit à partir des sécrétions de la glande de Dufour, il a un effet dissuasif qui dure environ 32 heures après son émission.La séquence des actes comportementaux de Nemeritis montre un accroissement significatif de réactions de fuite et d'évitement face à des chenilles d'Ephestia traitées superficiellement avec du contenu des glandes de Dufour.Cet article prouve pour la première fois que Nemeritis réagit aussi bien à des marqueurs externes qu'internes. Un comportement analogue vis à vis de papier filtre imprégné du contenu des glandes de Dufour et de son constituant hénéicosane constitue une preuve que le contenu de la glande influe sur le comportement de l'hymenoptère et ainsi lui évite de superparasiter ses hôtes.

     

Effect of host density on searching behaviour of Nemeritis canescens (Hymenoptera: Ichneumonidae)

Observations were made over one hour of individual parasites, N. canescens, searching for their hosts, larvae of the moth Plodia interpunctella, at five different host densities. Records were made of the total number of hosts encountered at each density, the total number of eggs laid and the handling time per host.Holling's disc equation was found to fit the data well and gave estimates for rate of parasite search (a) and handling time (b) close to values actually observed. Despite the good fit, rate of search and handling time both declined as host density increased. The time spent handling already parasitised hosts, avoidance time was found to be about half the value of handling time.

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Resume Les observations ont été faites durant une heure sur des parasites isolés, N. canescens, prospectant des lots de chenilles de Plodia interpunctella — leurs hôtes — à cinq densités différentes. Pour chaque densité, ont été notés: le nombre total d'hôtes rencontrés, le nombre total d'ufs pondus et le temps d'examen par hôte.L'équation de Holling s'est bien adaptée aux données et a fourni des estimations pour le taux de prospection des parasites (a) et le temps d'examen (b) proches des valuers réellement observées. Malgré une bonne adaptation, le taux de prospection et le temps d'examen diminuent tous deux quand la densité de l'hôte augmente. Le temps dépensé à l'examen des hôtes déjà parasités, temps de rejet correspond à environ la moitié du temps d'examen.

     

Differences in egg wastage by superparasitism,contrastingVenturia (=Nemeritis) canescens searching singly versus searching in groups

A statistical and graphic study is presented of the wastage of eggs by Venturia (=Nemeritis) canescens when searching singly and in groups of 10 among hosts at four different host densities in laboratory universes as described byHuffaker andMatsumoto (preceding paper of this journal). The host insect was the fluour moth Anagasta kühniella and the host densities used were 10, 30, 100 and 200 per universe. Intensity of egg wastage due to superparasitim varied significantly according to host density, and between the two parasite densities employed, 1 and 10, using both F-tests and chi-square tests. Plots of k-factor analysis on this egg wastage showed high negative correlations with host density, and the raw data for single parasites was well represented by a parabola while that for the grouped parasites departed from this relationship only at the lowest host density.     

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.     

Sex-determination and biology of a parasitic wasp, Hadrobracon brevicornis (Wesmael)

Ohne Zusammenfassung

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Sex-determination and biology of a parasitic wasp, Hadrobracon brevicornis (Wesmael)

     

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.     

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.     

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.     

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.     

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     

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.     

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.     

Beta-ionone is a functional plant volatile that attracts the parasitic wasp,Microplitis pallidipes

BioControl - The effects of plant volatiles on parasitoids are important with regards to the tri-trophic interactions among host plants, insect herbivores, and their natural enemies. However, the...     

Electroantennogram responses of a parasitic wasp, Microplitis croceipes, to host-related volatile and anthropogenic compounds

The parasitic wasp Microplitis croceipes (Cresson) (Hymenoptera: Braconidae) showed its own characteristic electroantennogram (EAG) response profiles to 13 host‐related (cis‐3‐hexenol, α‐pinene (R)‐(+)‐limonene (S)‐(–)‐limonene, trans‐β‐ocimene (±)‐linalool, (–)‐trans‐caryophyllene, α‐humulene, nerolidol, trans‐nerolidol, cis‐nerolidol, methyl jasmonate and indole) and four anthropogenic (2‐diisopropylaminoethanol, 2,2′‐thiodiethanol, 2‐methyl‐5‐nitroaniline and cyclohexanone) volatile compounds. These profiles were similar between males and females except for 2‐diisopropylaminoethanol, which elicited significantly larger EAG responses in males. Among the compounds tested, cis‐3‐hexenol, linalool and cyclohexanone elicited the largest EAG responses. EAG responses were not influenced by the age of wasps between 1 and 13 days after emergence. EAG responses were dose‐dependent, and highly EAG‐active compounds elicited significant EAG responses with less than 10 μg of the compounds at source. Quantification of compounds released from an odour cartridge indicates that release rate is highly dependent on the chemical nature of stimuli, showing up to 10 000‐fold differences in the amount released between different compounds when the same amount was loaded in the odour cartridge. Wasps having undergone a behavioural training regime to be attracted to either cyclohexanone or methyl jasmonate did not show any differences in EAG responses from those of untrained wasps.