Deuterium marking of chemical emissions: detectability and fitness consequences of a novel technique for insect behavioural studies

Behavioural studies often need to employ marking techniques to identify and track individuals. Marks ideally have no influence on behaviour or fitness of marked individuals or on the organisms with which they interact. A newly developed internal marking technique uses deuterium to manipulate the chemical emissions of bethylid wasps that are parasitoids of lepidopteran larvae. Wasps are deuterated indirectly by injecting deuterium oxide (heavy water) into the host on which they feed as larvae. Adult wasps emit a volatile chemical under stressful conditions and the emissions of deuterated and undeuterated wasps can be clearly and readily distinguished by measuring the ratio of deuterated/undeuterated molecules using real‐time mass spectrometry. Deuterated female wasps are, however, detectably disadvantaged in dyadic contests for host resources, a component of female fitness. In this study, we evaluated potential side‐effects of this deuterium marking technique on three further correlates of female Goniozus legneri Gordh (Hymenoptera: Bethylidae) fitness: longevity, lifetime fecundity, and offspring developmental mortality. We found that deuterium enrichment has no overall adverse effects on these parameters. We further showed that injecting hosts with different concentrations of deuterium results in distinguishably different volatile emissions of adult wasps, such that at least three individuals can be simultaneously identified by their chemical signatures. We also showed that deuterium marking remains effective beyond a wasp's death: deuterated and undeuterated wasps remain readily distinguishable after storage. We discuss potential applications of deuterium marking for the laboratory and field study of chemical communication, dispersal, and mating structure in parasitoid wasps and other insects.     

Consequences of infanticide for a gregarious ectoparasitoid of leafroller larvae

1. In this laboratory study, the clutch size and handling time of Goniozus jacintae were investigated, a comparison of its life‐history performance between primary and secondary (laid after infanticide events) broods was carried out, and the lipid and protein concentrations in the haemolymph of non‐parasitised and parasitised hosts were estimated. 2. It was found that G. jacintae temporarily paralysed its host larvae for 66 min and briefly guarded its brood for 66 min. The clutch size of G. jacintae increased from two to seven with increasing larval fresh weight of its host, and both ovicide and larvicide of primary clutches occurred in 81% of encounters. 3. Secondary clutches of G. jacintae were significantly larger than primary clutches in two of three ovicide treatments for the same host individuals. Secondary clutches also experienced greater brood survivorship than primary clutches. 4. Lipid concentrations were consistently higher in the haemolymph of parasitised hosts, and protein concentrations were initially higher (until egg hatch), but increased at a lower rate in parasitised hosts than in non‐parasitised hosts. 5. This study is the first to provide evidence that improved nutritional quality could be an important benefit of infanticide for an insect parasitoid, allowing for larger clutch size and improved brood survivorship among secondary broods.     

Observations on the oviposition behaviour ofGoniozus sensorius [Hymenoptera: Bethylidae] a parasite ofDiaphania indica [Lepidoptera: Pyralidae]

Goniozus sensorius Gordh (Hymenoptera: Bethylidae) was recorded as a major parasite of the pumpkin caterpillar,Diaphania indica (Saunders) (Lepidoptera: Pyralidae). This paper provides detailed information on the oviposition behaviour ofG. sensorius. Prior to oviposition, the parasite temporarily paralyses the host larva. The paralysed condition lasts for about 2 h. The egg laying process on each larva requires 30 to 60 min. The maximum number of eggs are laid on the 6^th and 7^th segment, and none in the terminal segments. Generally, oviposition is restricted to 1 segment of the host larva and occasionally on 3 segments. The maximum number of eggs are laid on the 2^nd and 3^rd day after emergence and the mean number of eggs laid on each host larva was 7.1.     

浙江省棱角肿腿蜂属种类记述（膜翅目：肿腿蜂科：肿腿蜂亚科）

我国已知棱角肿腿蜂属 Goniozus Forster,1 856四种 ,即日本棱角肿腿蜂 G.japonicus Ashmead,1 90 4;中华棱角肿腿蜂 G.sinicus Xiao et Wu,1 987;蓬莱棱角肿腿蜂 G.hoorai Terayama,1 999和八重山棱角肿腿蜂 G.yaeyamanus Terayama,1 999。本文记述浙江省棱角肿腿蜂属 4种 ,其中除日本棱角肿腿蜂 Goniozusjaponicus Ash-mead,1 90 4为已知种外 ,其余 3个为新种 ,即 :萧氏棱角肿腿蜂 Goniozus xiaoi,sp.nov.,百山祖棱角肿腿蜂 Goniozus baishanzuensis,sp.nov.和豆卷螟棱角肿腿蜂 Go-niozus lamprosemae,sp.nov.。这样使中国棱角肿腿蜂属增加到 7种。1 .萧氏棱角肿腿蜂 Goniozus xiaoi,新种 (图 1～ 5)该新种与分布于日本和我国台湾的蓬莱棱角肿腿蜂 G.hoorai Terayama,1 999较相似 ,但新种触角第 2至 5节各节长明显大于宽 ;并胸腹节背表面后缘的横脊不完整 ,仅在并胸腹节的后侧角可见。正模 :♀ ,浙江庆元百山祖 ( 2 7.45°N,1 1 9.1 2°E) ,1 993 - -0 6,吴鸿 ,No.9452 91。副模 :1♀ ,浙江松阳 ( 2 8.2 7°N,1 1 9.2 9°E) ,1 994- -0 7,陈汉林 ,No.948481。2 .百山祖棱角肿腿蜂 Goniozus baishanzuensis,新种 (图 6～ 1 0 )本新种的触角与日本棱角肿腿蜂 Goniozusjaponicus Ashmead,1 90 4的触角     

Co‐foundress confinement elicits kinship effects in a naturally sub‐social parasitoid

Kinship among interacting individuals is often associated with sociality and also with sex ratio effects. Parasitoids in the bethylid genus Goniozus are sub‐social, with single foundress females exhibiting post‐ovipositional maternal care via short‐term aggressive host and brood defence against conspecific females. Due to local mate competition (LMC) and broods normally being produced by a single foundress, sex ratios are female‐biased. Contests between adult females are, however, not normally fatal, and aggression is reduced when competing females are kin, raising the possibility of multi‐foundress reproduction on some hosts. Here, we screen for further life‐history effects of kinship by varying the numbers and relatedness of foundresses confined together with a host resource and also by varying the size of host. We confined groups of 1–8 Goniozus nephantidis females together with a host for 5+ days. Multi‐foundress groups were either all siblings or all nonsiblings. Our chief expectations included that competition for resources would be more intense among larger foundress groups but diminished by both larger host size and closer foundress relatedness, affecting both foundress mortality and reproductive output. From classical LMC theory, we expected that offspring group sex ratios would be less female‐biased when there were more foundresses, and from extended LMC theory, we expected that sex ratios would be more female‐biased when foundresses were close kin. We found that confinement led to the death of some females (11% overall) but only when host resources were most limiting. Mortality of foundresses was less common when foundresses were siblings. Developmental mortality among offspring was considerably higher in multi‐foundress clutches but was unaffected by foundress relatedness. Groups of sibling foundresses collectively produced similar numbers of offspring to nonsibling groups. There was little advantage for individual females to reproduce in multi‐foundress groups: single foundresses suppressed even the largest hosts presented and had the highest per capita production of adult offspring. Despite single foundress reproduction being the norm, G. nephantidis females in multi‐foundress groups appear to attune sex allocation according to both foundress number and foundress relatedness: broods produced by sibling foundresses had sex ratios similar to broods produced by single foundresses (ca. 11% males), whereas the sex ratios of broods produced by nonsibling females were approximately 20% higher and broadly increased with foundress number. We conclude that relatedness and host size may combine to reduce selection against communal reproduction on hosts and that, unlike other studied parasitoids, G. nephantidis sex ratios conform to predictions of both classical and extended LMC theories.     

Bio-assay study of response by a parasitoid to frass and feeding substrates of its host, the stalk borer Eldana saccharina

In Petri dish and olfactometer tests Goniozus natalensis Gordh (Hymenoptera: Bethylidae) exhibited a host-searching response upon contact with, and at a short distance from, frass of its natural host, Eldana saccharina Walker (Lepidoptera: Pyralidae), whichever the substrate on which E. saccharina had been feeding. The substrates were two host plants, sugarcane or Cyperus papyrus L.; diet media based respectively on sugarcane, papyrus, or cellulose; or a synthetic diet medium, containing no plant material. Host-searching behaviour increased in intensity with age and after mating of G. natalensis females. Parasitoids responded similarly to frass produced by male and female E. saccharina larvae. The substrates themselves elicited little response in G. natalensis. Frass of another borer, Sesamia calamistis Hamps. (Lepidoptera: Noctuidae), fed on sugarcane-based medium, also elicited little response in G. natalensis. The results suggest that frass of E. saccharina larvae contains a material, evidently volatile, to which their parasitoid G. natalensis responds, irrespective of the substrate on which the E. saccharina subsist.     

Brood guarding in a bethylid wasp

Abstract.

• 1 Atypical of the parasitoid Hymenoptera, female Goniozus nephantidis Muesebeck remain with offspring until they pupate. This behaviour will only have evolved if the consequent reduction in fecundity is outweighed by fitness returns.
• 2 G.nephantidis competes for hosts with conspecific and non-conspecific parasitoids. The effectiveness of G.nephantidis at deterring superparasitism and multiparasitism is tested. Brood survivorships were compared when G.nephantidis and Bracon hebetor Say intrude on hosts with the mother present and absent and with offspring at different developmental stages.
• 3 Laying by the intruder reduced brood survivorship. Guarding reduced oviposition on unparasitized hosts by intruding females, and prevented superparasitism of hosts with egg broods. Hosts with larval broods were rarely superparasitized. Multiparasitism was common except on hosts with guarded larval broods, but even here survivorship was reduced.
• 4 Competitive asymmetries determined the outcome of contests for possession of host resources.
• 5 The costs of remaining seem at least partially offset by the prevention of oviposition by competing parasitoids.

     

Brood sex ratio variance,developmental mortality and virginity in a gregarious parasitoid wasp

Females of the parasitoid wasp Goniozus nephantidis paralyse host caterpillars and lay a clutch of up to 18 eggs onto the host integument. The known biology of G. nephantidis suggests that matings occur exclusively between siblings from the same brood. This leads to the prediction that brood sex ratios should be highly female-biased and have low variance. Sex ratios are indeed female-biased, with the mean proportion of males equal to 0.093. However, while sex ratio variance is significantly less than binomial, many broods contain no males at emergence. During development 28% of G. nephantidis offspring die. Male mortality offers a potential explanation for all-female (= virgin) broods. For the clutch sizes and mortality observed, theory predicts that <10% of females will emerge from all-female broods but the empirical value is much higher. The prediction that the prevalence of virginity decreases with increasing clutch size is, however, supported. We consider alternative explanations for the observed proportion of all-female broods, but this appears to be neither an artefact of the laboratory environment nor due to incorrect assumptions about G. nephantidis life history. Although its reproductive biology has been much investigated and its sex ratio matches some theoretical predictions, we conclude that a fuller understanding of G. nephantidis sex ratio requires a deeper knowledge of its field biology.     

15N-enrichment of plant tissue to mark phytophagous insects, associated parasitoids, and flower-visiting entomophaga

New techniques are presented on the use of ¹⁵N to mark insects. ¹⁵N, a stable isotope of nitrogen, was enriched above natural abundance in plant and insect tissues. Two laboratory studies demonstrated that enriched ¹⁵N-concentrations could be tracked from plant to insect using mass spectrometry. In the first study, adult Cotesia plutellae (Kurdjimov) (Hymenoptera: Braconidae) and Hippodamia convergens Guérin-Méneville (Coleoptera: Coccinellidae) were allowed to feed at the flowers of rapid-cycling Chinese cabbage plants that had been fertilized with ¹⁵N-enriched potassium nitrate (KNO₃-¹⁵NO₃). Both insect groups were found to have significantly elevated ¹⁵N levels after visiting the flowers of the ¹⁵N-enriched plants for 48 hours. In the second study, ¹⁵N-enriched bean plant (Phaseolus vulgaris L.) tissue was incorporated into an insect diet and fed to navel orangeworms, Amyelois transitella (Walker) (Lepidoptera: Pyralidae). When the navel orangeworm larvae were 4th instars, they were removed from the diet and exposed to the parasitoid, Goniozus legneri Gordh (Hymenoptera: Bethylidae). Results indicated that the enriched ¹⁵N-concentration of the bean plants was transferred to the navel orangeworms and, subsequently, to the parasitoids. This work may provide useful techniques to help establish whether agriculturally important entomophaga visiting ¹⁵N-enriched flowers or parasitizing enriched sentinel larvae in the field can be effectively marked with ¹⁵N.