The effect of different dietary sugars and honey on longevity and fecundity in two hyperparasitoid wasps

In nature adult insects, such as parasitic wasps or 'parasitoids' often depend on supplemental nutritional sources, such as sugars and other carbohydrates, to maximize their life-expectancy and reproductive potential. These food resources are commonly obtained from animal secretions or plant exudates, including honeydew, fruit juices and both floral and extra-floral nectar. In addition to exogenous sources of nutrition, adult parasitoids obtain endogenous sources from their hosts through 'host-feeding' behavior, whereby blood is imbibed from the host. Resources obtained from the host contain lipids, proteins and sugars that are assumed to enhance longevity and/or fecundity. Here we conducted an experiment exploring the effects of naturally occurring sugars on longevity and fecundity in the solitary hyperparasitoids, Lysibia nana and Gelis agilis. Although both species are closely related, L. nana does not host-feed whereas G. agilis does. In a separate experiment, we compared reproduction and longevity in G. agilis reared on either honey, a honey-sugar 'mimic', and glucose. Reproductive success and longevity in both hyperparasitoids varied significantly when fed on different sugars. However, only mannose- and water-fed wasps performed significantly more poorly than wasps fed on four other sugar types. G. agilis females fed honey produced twice as many progeny as those reared on the honey-sugar mimic or on glucose, whereas female longevity was only reduced on the mimic mixture. This result shows not only that host feeding influences reproductive success in G. agilis, but also that non-sugar constituents in honey do. The importance of non-sugar nutrients in honey on parasitoid reproduction is discussed.     

Spruce stands provide natural food sources to adult hymenopteran parasitoids of bark beetles

Adults of synovigenic hymenopteran parasitoids of bark beetles need supplemental feeding to maximise their lifetime realised fecundity, and yet little is known about the natural sources that provide this food. Here we show that, in spite of the reduced diversity of flowering plants expected in even-aged spruce plantations, several plant species are present that might provide nectar and pollen to the hymenopteran parasitoid complex of Ips typographusL. (Coleoptera: Scolytidae), throughout the growing season. Conifer aphids are also abundant in these stands and produce large amounts of honeydew, which might also be consumed by the parasitoids. Laboratory experiments demonstrate that longevity is significantly increased in Coeloides bostrychorum Giraud (Hymenoptera: Braconidae) when the wasps are exposed to flowers of various species commonly found in spruce stands.     

Fecundity and Longevity of Green Vegetable Bug,Nezara viridula, Following Parasitism byTrichopoda giacomellii

The effects of parasitism by the ArgentinianTrichopoda giacomellii(Blanchard) on reproduction and longevity of its host,Nezara viridula(L.) are reported. Parasitoid larvae suppress egg maturation, reducing by 70% the fecundity of mature female hosts during the period of larval development. Egg viability was not affected, but mating frequency was reduced by approximately 50%. When parasitized as newly eclosed adults, 84% of females fail to reproduce. In male hosts, fertility and mating frequency were not affected during the period of larval parasitoid development. In male and reproductively immature female hosts, death was coincident with, or occurred shortly after parasitoid emergence (2–4 days); in mature females, death occurred on average 2 weeks after larval parasitoid emergence. Host mortality occurred as a consequence of tissue damage incurred as the parasitoid larvae emerged from the host. Some individuals survived parasitism though no further reproductive activity (mating or oviposition) occurred. The effectiveness ofT. giacomelliias a biological control agent is discussed in relation to its impact on reproduction and survival of its host and contrasted with the action of otherTrichopodaspecies.     

Comparative Development and Performance of Artificially Reared versus Host-RearedDiapetimorpha introita(Cresson) (Hymenoptera: Ichneumonidae) Wasps

Diapetimorpha introita(Cresson) (Hymenoptera: Ichneumonidae), a native ectoparasitoid ofSpodopteraspp. pupae, was reared in the laboratory on an artificial diet devoid of any insect host components. Diet-reared wasps demonstrated a propensity to search for and parasitize natural hosts in a field cage trial. Longevity of the diet-reared wasps was comparable with the longevity of wasps reared on host pupae. Survival rate ofD. introitawas 61.3% when reared on diet and 76.3% when reared on host pupae. Wasps reared on the artificial diet had longer developmental times, reduced fecundity, and reduced adult weights compared to wasps reared on host pupae. These studies suggest that future research efforts should focus on increasing fecundity and weight of diet-reared wasps and decreasing the mortality and developmental time of wasps reared on the artificial diet. The ability to rearD. introitaon an inexpensive, artificial diet significantly enhances the potential of mass rearing this parasitoid for inundative releases againstSpodopteraspp.     

Costs and Benefits of Food Foraging for a Braconid Parasitoid

The costs and benefits of food foraging for the insect parasitoid, Phanerotoma franklini Gahan (Hymenoptera: Braconidae), were examined. Feeding benefited P. franklini by increasing longevity, but did not influence egg maturation. Costs of feeding are represented by the time required to locate and consume food. Field observations of starved wasps revealed that wasps spent approximately 25% of their time grazing on substances on the surface of cranberry foliage. However, our initial laboratory tests to determine the value of these substances were inconclusive. We also examined how grazing behavior integrated with host foraging by comparing the attack rate of fed and unfed wasps held under different host densities. While feeding status did not affect the mean attack rate of wasps, starvation enhanced the probability that a wasp will engage in movement over the host plant foliage. We conclude that feeding benefits P. franklini by increasing longevity, that travel time to food sources is likely to be low, and that the observed food-foraging behavior does not appear to influence host-foraging efficiency.     

Modelling age‐ and density‐structured reproductive biology and seasonal survival of Apanteles galleriae Wilkinson (Hym., Braconidae)

Abstract: The biology of Apanteles galleriae Wilkinson, an important biological control agent of wax moths, is well described in the literature. We developed models simulating the functional response of fecundity and female progeny proportion of adult females as a function of age, host and/or parasitoid density to integrate current knowledge. Daily pattern of age‐related fecundity and female progeny proportion of different parasitoids was also examined. We investigated the effect of sex, mating status and seasonal time on adult longevity. We derived survival data of females in two different seasonal periods. We found that 50% of adult life span is important for an efficient fecundity. The patterns of host and/or parasitoid density‐dependent fecundity and sex ratio varied considerably. The highest fecundity and female progeny proportion occurred with one parasitoid and one female equivalent host. Longevity of adults was affected by sex and month periods, but mating status did not affect their longevity. Female survival was greater between December and May relative to June and November. Our results indicated that age, host and parasitoid density, and the timing of rearing influenced the life processes of parasitoids.     

Fecundity and oviposition ofEucelatoria bryani, a gregarious parasitoid ofHelicoverpa zea andHeliothis virescens

We examined longevity, fecundity, and oviposition strategies ofEucelatoria bryani Sabrosky (Diptera: Tachinidae), a gregarious endoparasitoid ofHelicoverpa zea (Boddie) andHeliothis virescens (F.) (Lepidoptera: Noctuidae). Longevity of adult femaleE. bryani was not related to body size. In contrast to longevity, largerE. bryani females had greater potential fecundity than smaller females, as determined by the number of embryonated eggs present in the common oviduct. However, female parasitoid size did not affect primary clutch size (number of eggs deposited in a host). Because embryos in eggs located in the ovisac were larger than those located elsewhere in the common oviduct, maximum primary clutch size may be physiologically limited by the number of fully mature eggs a female has available at one time.E. bryani females adjusted primary clutch size in response to host size, for bothH. zea andH. virescens. This adjustment appears to be adaptive because females did not overexploit hosts by depositing more larvae than a host could support. Adult emergence was not related to host size. Although host weight positively influencedE. bryani progeny weight, increases in progeny size with host size were counterbalanced by increases in primary clutch size with host size.     

Discriminating between energetic content and dietary composition as an explanation for dietary restriction effects

A reduction in dietary calories has been shown to prolong life span in a wide variety of taxa, but there has been much debate about confounding factors such as nutritional composition of the diet, or reallocation of nutrients from reduced reproduction. To disentangle the contribution of these different mechanisms to extension of life span, we study the effect of caloric restriction on longevity and fecundity in two species of sugar-feeding parasitoid wasps. They have a simple diet that consists of carbohydrates only, and they do not resorb eggs, which rules out the proposed alternative explanations for beneficial effects of caloric restriction. Two caloric restriction treatments were applied: first, dietary dilution to investigate the effect of carbohydrate concentration in the diet; and second, intermittent feeding to examine the effect of feeding frequency on longevity and fecundity. Only the dietary dilution treatment showed an effect of caloric restriction with the highest longevity recorded at 80% sucrose (w/v). No effect of dietary regime was found on fecundity. We also measured the weight increase of the parasitoids after feeding to obtain an estimate of consumption. A constant quantity of the sugar solution was consumed in all dietary dilution treatments, hence caloric intake was proportional to sucrose concentrations. Although the present study does not disqualify the relevance of nutrient composition in other species, our data unequivocally demonstrate that caloric restriction alone is sufficient to extend life span and invalidate alternative explanations.     

Feeding strategies in drosophilid parasitoids: the impact of natural food resources on energy reserves in females

1. Adult feeding strongly increases longevity and fecundity in parasitic wasps. Searching for food resources involves costs; therefore, it is advantageous to be able to feed on the breeding substrate.
2. Cohorts of females of four drosophilid parasitoid species were assigned to different food treatments including starvation. Fat contents were measured and compared after 5 days. In this way the nutritional value of breeding substrates to females could be expressed in terms of energy reserves.
3. Three of the four species tested fed on natural breeding substrates. A fourth species did not produce evidence of such feeding. However, this species fed on honey when fat reserves were low.
4. Feeding is related to: (i) the species' natural breeding substrate, (ii) the energy allocation and lifetime expectancy of the female, and (iii) time of the season.
5. Because feeding strongly influences longevity and fecundity, it is argued that the different feeding strategies found may affect competitive relationships between these drosophilid parasitoid species.     

Feeding and survival in parasitic wasps: sugar concentration and timing matter

Sugar consumption can increase the longevity and lifetime fecundity of many species of parasitic wasps. Consequently, for these insects the availability of sugar sources in the field is important for their reproductive success. As sugar sources can be highly variable in quantity, space and time, the chances of finding a sufficient amount of sugar to increase longevity might be very low. Therefore, the reward from a single feeding event can be critical for the forager's fitness. We measured the longevity of the parasitoid Cotesia rubecula after a single honey meal differing in sugar concentration (25, 47, 86% w/w) and timing (day of emergence and 24 h later). Survival was analysed with Cox's Proportional Hazards Model. The risk of starving to death in sugar-fed wasps was reduced by 0–73% in comparison to unfed wasps, depending on sugar concentration and timing. Longevity was significantly increased by sugar concentration and by feeding later in life. Our results suggest that in the field, adult C. rubecula has to locate food at least once per day to avoid starvation.