Superparasitism strategy in a semisolitary parasitoid with imperfect self/non-self recognition, Echthrodelphax fairchildii

To assess the adaptiveness of self‐ and conspecific superparasitism in the parasitoid Echthrodelphax fairchildii Perkins (Hymenoptera: Dryinidae), we measured the rate of superparasitism avoidance and fitness returns from superparasitism for different intervals between the first and second ovipositions. We also tested for any preference in oviposition side and whether any such preference was adaptive. The rate of superparasitism avoidance in both self‐ and conspecific superparasitism was about 10% for oviposition intervals of 2–8 h, and higher for intervals of 1 and ≥24 h (but did not exceed 35%). When conspecifically superparasitizing (but not self‐superparasitizing), females exhibited a slight preference for the side without the first‐comer. Under conspecific superparasitism, the survival rate of second comers was independent of the oviposition side and interval, but slightly lower than that of immature parasitoids for single parasitism. The adult size of second‐comers on the side harboring the first‐comer was larger than that of second‐comers on the side without it, when the oviposition interval was <24 or 96 h. These results explained the overall low rate of avoidance of conspecific superparasitism, but not the variation in avoidance rate or the preference for side without the first‐comer when conspecifically superparasitizing. Assuming that fitness returns are influenced more by offspring quantity than by their quality, self‐superparasitism produced positive fitness returns only when the oviposition interval was <24 h and the side without the first‐comer was selected. This suggests that the observed behavior was not adaptive. Possible reasons for the discrepancies between observed and optimal behaviors, including an imperfect ability for self/non‐self recognition, are discussed.     

Self-/conspecific discrimination and superparasitism strategy in the ovicidal parasitoid Echthrodelphax fairchildii （Hymenoptera： Dryinidae）

Superparasitism in solitary parasitoids results in fatal competition between the immature parasitoids, and consequently only one individual can emerge. In the semisoli- tary ovicidal parasitoid Echthrodelphaxfairchildii （Hymenoptera： Dryinidae）, 2 adults can emerge under superparasitism with a short interval （〈24 h） between the first and second ovipositions. We determined the female parasitoid＇s behavioral responses under self- and conspecific superparasitism bouts with first-to-second oviposition intervals of 〈2 h. The self- and conspecific superparasitizing frequencies increased up to an oviposition interval of 0.75 h, with the former remaining lower than the latter, particularly for oviposition intervals of _〈0.25 h, suggesting the existence of self-/conspecific discrimination. The superparasitizing frequency plateaued for oviposition intervals of _〉0.75 h, with no dif- ference between self- and conspecific superparasitism. The ovicidal-probing frequency did not differ under self- and conspecific superparasitism, and was usually 〈20%. The females exhibited no preference for the oviposition side （i.e., ovipositing on the side with or without the first progeny） and almost always laid female eggs for any oviposition in- terval under self- and conspecific superparasitism. The sex ratio was not affected by the type of superparasitism, oviposition sides, or the occurrence of ovicidal probing. These observed results about the oviposition side, ovicidal probing, and sex ratios differed from the predictions obtained assuming that the females behave optimally. Possible reasons for the discrepancies are discussed： likely candidates include the high cost of selecting oviposition sides and ovicidal probing, and, for the sex ratio, the low frequency of encountering suitable hosts before superparasitism bouts.     

Profitable self-superparasitism in an infanticidal parasitoid when conspecifics are present: self-superparasitism deters later attackers from probing for infanticide

Abstract.  1. To reveal the profitability of self-superparasitism when conspecifics are present, the total combined fitness returns from the first and second ovipositions under triple parasitism were compared with fitness returns from the first oviposition under double parasitism, using the small brown hopper Laodelphax striatellus and its semi-solitary infanticidal parasitoid Echthrodelphax fairchildii .
2. The total combined survival rate of the first and second comers under triple parasitism with oviposition intervals of 1/24 h (where 1 and 24 h represent the first-to-second and second-to-third oviposition intervals respectively) was nearly double the survival rate of the first comer under double parasitism with a 25-h oviposition interval, although there was no difference between these triple and double parasitisms in terms of head width and developmental time. Under the conditions of other oviposition intervals, self-superparasitism produced null (1/1- and 24/24-h intervals) or negative fitness returns (24/1-h intervals). This suggests that self-superparasitism on hosts that were self-parasitised 1 h previously is profitable when conspecifics are present.
3. When the female parasitoid laid an egg on a host harbouring the earlier comer(s) on the non-oviposition side, she often probed the non-oviposition side for infanticide, i.e. killing the first offspring. When the first and second comers were on different sides, the probing frequency at the third oviposition in triple parasitism with 1/24-h oviposition intervals was lower than that at the second oviposition in double parasitism with a 25-h oviposition interval. This difference was responsible for the above difference in survival rate between the triple and double parasitisms.     

Presence of a conspecific increases superparasitism but not infanticide under self‐ and conspecific superparasitism in a semisolitary parasitoid,Echthrodelphax fairchildii (Hymenoptera: Dryinidae)

Female parasitoids are expected to avoid superparasitism (ovipositing in and/or on parasitized hosts) when unparasitized hosts are available. However, when the supply of unparasitized hosts is restricted, they are expected to self‐ as well as conspecifically superparasitize. One of the cues of a reduced availability of unparasitized hosts is the presence of a conspecific. Moreover, if the focal species can perform infanticide, after encountering a conspecific female, the females are expected to kill eggs existing in and/or on hosts when superparasitizing, because the eggs are more likely to be laid by others. In this study we investigated whether females of an infanticidal semisolitary parasitoid, Echthrodelphax fairchildii, increase their frequencies of superparasitism and infanticide after encountering a conspecific female. Echthrodelphax fairchildii females are capable of discriminating between self‐ and conspecific superparasitism until up to 0.75 h after the first egg was laid (self‐superparasitism frequency < conspecific superparasitism frequency). As expected, the female parasitoids were more likely to perform self‐ and conspecific superparasitism after they had encountered a conspecific. In particular, the self‐superparasitism frequency increased highly within a short period after the first oviposition, so that no difference between the self‐ and conspecific superparasitism frequencies was found. In contrast, the infanticidal‐probing frequency remained extremely low, irrespective of whether or not the female parasitoids had encountered a conspecific. Moreover, when superparasitizing, females usually laid female eggs. Possible causes for the low frequency of infanticidal probing and the female‐biased sex ratio are discussed.     

Imperfect preference for singly parasitized hosts over doubly parasitized hosts in the semisolitary parasitoid Echthrodelphax fairchildii: implications for profitable self-superparasitism

Self‐superparasitism can be profitable (i.e., a fitness gain) when conspecific female adult parasitoids prefer singly parasitized hosts over doubly parasitized hosts. This preference is expected to evolve when the value (i.e., the fitness gain from oviposition) of doubly parasitized hosts is lower than that of singly parasitized hosts. We examined whether such a preference is found in the small brown planthopper, Laodelphax striatellus (Fallén) (Homoptera: Delphacidae), and its semisolitary infanticidal parasitoid Echthrodelphax fairchildii Perkins (Hymenoptera: Dryinidae). We compared the preferences and host values between each of four pairs of double and triple parasitism, each of which had the same time interval between the first and last oviposition bouts. Ovipositions on doubly and singly parasitized hosts occurred with similar frequencies in each of the four pairs, even though the doubly parasitized hosts were of lower value than the singly parasitized hosts. However, the value of doubly parasitized hosts with the first and second parasitoid offspring on the same side of the host was higher than that of hosts with the two offspring on different sides, and the value of the former did not differ significantly from that of singly parasitized hosts. The preferences between singly and doubly parasitized hosts with the two offspring on the same or different sides were as expected from differences in their values, except for one pair of double and triple parasitisms. This exception is considered attributable to an imperfect ability to evaluate hosts.     

Vulnerability window for laying male eggs and superparasitism in producing female offspring of Encarsia sophia on Bemisia tabaci B biotype

Encarsia sophia (Girault & Dodd) (Hymenoptera: Aphelinidae) is an autoparasitoid that produces male offspring by laying unfertilized eggs in conspecific or heterospecific immature parasitoids at a particular stage of development known as the “vulnerability window”. In the work discussed in this paper, the early vulnerability window in which parasitoid wasps lay unfertilized eggs was determined by exposing parasitized Bemisia tabaci (Gennadius) (Homoptera: Aleyrodidae) nymphs to female E. sophia wasps at 12-h intervals. Because superparasitism affected the results of mass-rearing of parasitoids, especially for autoparasitoids, the effects of superparasitism on development time for female offspring were investigated. Furthermore, the effects of the ratio of wasps to nymphs and the effects of inoculation interval on superparasitism were also determined. The superparasitization behavior was observed in the laboratory. Results indicated that female wasps could produce male offspring in nymphs that had been parasitized five days previously. Wasp offspring were 40.54 and 59.42 % male when exposed nymphs were parasitized 5 and 5.5 days previously, respectively. Superparasitism significantly prolonged the duration of development of female offspring, which increased from 11.5 days for one parasitization to 15.8 days for three parasitizations. Exposure interval also affected superparasitism: when the interval was increased from 0 to 96 h, superparasitism decreased from 70.0 to 23.8 %. With increasing parasitization, the time wasps spent on internal probing plus oviposition increased from 147.4 s for the first parasitization of nymphs to 285.4 s for the third parasitization, whereas there was no significant difference in the time wasps spent on external inspection of nymphs that had been parasitized one, two, or three times. When the ratio of wasps to nymphs was increased from 1:10 to 5:10, superparasitism increased from 0.4 to 46.4 %.     

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.

     

The pay-off from superparasitism in the egg parasitoid Trissolcus basalis, in relation to patch defence

1. In species such as quasi-gregarious egg parasitoids, which exploit defendable patches, the fitness pay-off from superparasitism is an important factor in considering the evolution of patch defence and optimal patch defence strategies.
2. When oviposition in a previously parasitized host has a non-zero fitness pay-off, competing parasitoids are not only able to diminish the future value of a patch to other females by depleting unparasitized hosts, but also devalue the previous investment of other females in the patch by superparasitizing.
3. In Trissolcus basalis , an egg parasitoid of pentatomid bugs, the fitness pay-off from superparasitism is higher than 0.5 when the time interval between ovipositions is less than 3 h, suggesting that defending a previous investment will be an important component of patch defence behaviour.
4. The data suggest a mechanism for the high early pay-off, which involves the superparasitizing female adjusting the sex ratio of its offspring in favour of males. Males develop more quickly than females and thus may have a competitive advantage.     

Hyperparasitism in a Generalist Ectoparasitic Pupal Parasitoid,Pachycrepoideus vindemmiae (Hymenoptera: Pteromalidae), on Its Own Conspecifics: When the Lack of Resource Lead to Cannibalism

Hyperparasitism is a normal behavior of parasitoids, which often happens among species. Conspecific hyperparasitism, such as some kinds of heteronomous hyperparasitic behaviors, has been only reported in some species belonging to Aphelinidae. In this article, the conspecific hyperparasitism of Pachycrepoideus vindemmiae (Pteromalidae) is reported, with Drosophila puparia as hosts. Hosts were exposed to P. vindemmiae females twice to parasitism with nine, twelve, and fifteen day intervals between the two exposures. None of the infested hosts emerged more than one offspring, and emergence of parasitoid offspring occurred in two obvious events, synchronously with the exposure time intervals, which suggested that offspring emerging during the first and second events would come from the primary and secondary parasitoids, respectively, and the inference with the developmental duration of offspring also indicated this. With two P. vindemmiae strains that could be identified by a simple sequence repeat marker, the above speculation of the origin of those offspring emerging during the two events was confirmed. Dissection of hosts exposed twice revealed a cannibalism behavior of larvae from the secondary foundresses on the primary conspecific pupae. Our results suggested a conspecific hyperparasitism behavior of the secondary parasitoids on the primary conspecifics. Measures showed a reduced body size for the adults from the conspecific hyperparasitism. Foundresses from the conspecific hyperparasitism had less fitness variables than those from primary parasitism, with shorter longevity, less life time fecundity, lower values of infestation degree, and lower success rate of parasitism. However, when the parasitoids from the conspecific hyperparasitism met healthy Drosophila puparia, their offspring would recover to normal size. Frequency of the conspecific hyperparasitism behavior enhanced with the decreasing of proportion of healthy hosts in the oviposition patch. The conspecific hyperparasitism of P. vindemmiae on the primary conspecifics would be helpful to last the population when healthy hosts are absent in the oviposition patch.     

Superparasitism in Cotesia glomerata: response of hosts and consequences for parasitoids

Abstract.  1. Superparasitism occurs in Cotesia glomerata (Hymenoptera: Braconidae), a gregarious endoparasitoid of Pieris spp. (Lepidoptera: Pieridae). The response of P. brassicae larvae to superparasitism and the consequences for the parasitoid were examined in order to elucidate the ecological significance of this behaviour.
2. Field surveys of a Swiss population revealed that C. glomerata brood sizes from P. brassicae larvae ranged from three to 158, and both the female ratio and the body weight of emergent wasps correlated negatively with brood size. In the laboratory, single oviposition on P. brassicae larvae did not produce any brood size larger than 62, but brood size increased with superparasitism.
3. Laboratory experiments demonstrated that both naive and experienced female wasps were willing to attack hosts that had been newly parasitised by themselves or conspecifics. Superparasitism reduced survivorship but increased food consumption and weight growth in P. brassicae larvae. Superparasitism lengthened parasitoid development and prolonged the feeding period of host larvae.
4. Despite a trade-off between maximising brood size and optimising the fitness of individual offspring, two or three ovipositions on P. brassicae larvae resulted in a greater dry female mass than did a single oviposition on the host. Thus, superparasitism might be of adaptive significance under certain circumstances, especially when host density is low and unparasitised hosts are rare in a habitat.     

Asymmetric larval competition between two species of solitary parasitoid wasps: the influence of superparasitism

Abstract.

• 1 We test the hypothesis that a solitary parasitoid wasp may gain in fitness if she lays more eggs in a host.
• 2 Using heterospecific superparasitism (=multiparasitism) between the solitary aphid parasitoids, Aphidius smithi Sharma & Subba Rao and Ephedrus californicus Baker, we show that (i) a superparasitizing female's chance that her offspring will survive competition is an increasing function of egg density, and (ii) survival among same-aged larvae is independent of the oviposition sequence.
• 3 These findings on asymmetric larval competition provide indirect evidence that supports two fundamental, but untested, assumptions underlying models of adaptive superparasitism between conspecific wasps.

     

Impact of mating status on egg-laying and superparasitism behaviour in a parasitoid wasp

Most parasitoid female wasps can distinguish between unparasitized and parasitized hosts and use this information to optimize their progeny and sex allocation. In this study, we explored the impact of mating on oviposition behaviour (parasitism and self‐ and conspecific superparasitism) on both unparasitized and already parasitized hosts in the solitary parasitoid wasp Eupelmus vuilleti (Crw.) (Hymenoptera: Eupelmidae). Virgin and mated females had the same oviposition behaviour and laid eggs preferentially on unparasitized hosts. The sex ratio (as the proportion of females) of eggs laid by mated females in parasitism and conspecific superparasitism was 0.67 ± 0.04 and 0.57 ± 0.09, respectively. Likewise, females laid more eggs in conspecific superparasitism than self‐superparasitism under our experimental conditions. These experiments demonstrate that E. vuilleti females can (i) discriminate between unparasitized and parasitized hosts and adapt the number of eggs they lay accordingly, and (ii) probably discriminate self from conspecific superparasitized hosts. Finally, mating does not appear to influence the host discrimination capacity, the ovarian function, or the oviposition behaviour.     

Evidence for adaptive self-superparasitism in the dryinid parasitoid Haplogonatopus atratus when conspecifics are present

Self-superparasitism – ovipositing in or on a host that was previously parasitized by the same individual – had generally been considered maladaptive for solitary parasitoids. Recently, however, some researchers have suggested that self-superparasitized hosts produce higher fitness returns per host than singly parasitized hosts when these hosts are parasitized by conspecifics. The present study is the first to verify this possibility in the parasitoid Haplogonatopus atratus . Fitness returns from the first and second ovipositions under triple parasitism were compared with those from the first oviposition under double parasitism. Fitness returns were assessed in terms of survival rate, adult size, and developmental time. No differences were found between the two groups in adult size and developmental time. When the interval between the second and third ovipositions was 1 h, the total survival rate of the first and second comers under triple parasitism was higher than the survival rate of the first comer under double parasitism, and as high as the total survival rate of two first comers under double parasitism. This suggests that the value of self-parasitized hosts is as high as that of unparasitized hosts. When the second-to-third interval of triple parasitism was 24 h, self-superparasitism produced no fitness returns. Moreover, fitness returns from ovipositing into self-superparasitized hosts were similar to those from ovipositing into singly parasitized hosts.     

Superparasitism and host size effects in Oomyzus sokolowskii, a parasitoid of diamondback moth

Many aspects of a parasitoid's biology may be affected by its host. Host size, for example, could affect parasitoid fitness, especially in gregarious parasitoids, in which the resource is used by multiple siblings. Oomyzus sokolowskii (Kurdjumov) (Hymenoptera: Eulophidae) is a gregarious larval–pupal endoparasitoid of the diamondback moth, Plutella xylostella L. (Lepidoptera: Plutellidae), a major pest of crucifers worldwide, and is able to superparasitize the host. This study focuses on the hypothesis that because resource availability is higher in larger hosts, parasitoids developing in larger hosts will fare better. However, superparasitized hosts are expected to yield larger numbers of parasitoid offspring of smaller body size. Results showed that superparasitism increased the number of parasitoid offspring produced per host and increased offspring longevity, but decreased offspring body size. However, developmental time and sex ratio of parasitoid offspring was similar among hosts parasitized once, twice, or three times. Regardless of superparasitism, parasitoids emerging from larger hosts that were fed honey solution lived longer than similarly fed progeny from smaller hosts (36.4 vs. 22.1 days). The results partially support the hypothesis that Oomyzus gained fitness from an increase in host size; moreover, superparasitism seems advantageous for Oomyzus due to increased offspring numbers and longevity.     

Heterospecific ovicide influences the outcome of competition between two endoparasitoids, Encarsia formosa and Encarsia luteola

Abstract.  1. Studies of inter-specific competition in parasitoids have largely focused on the outcome of within-host competition and the behavioural mechanisms by which female parasitoids prevent competition. Another, less well studied, possibility is oviposition preceded by 'heterospecific ovicide', the destruction of the other species' egg. Heterospecific ovicide essentially eliminates within-host competition.
2. This study investigated the mechanisms and outcome of within-host competition in Encarsia formosa and Encarsia luteola , solitary endoparasitoids of whitefly pests. These species are known to commit ovicide of conspecific eggs.
3. Competition experiments indicated that the offspring of second-ovipositing females had an apparent advantage in competition, regardless of whether the second female was E. formosa or E. luteola .
4. Observations of ovipositor movement through the cuticle of host whitefly nymphs showed that both species often committed heterospecific ovicide and then oviposited or host-fed. Multiparasitism and heterospecific host discrimination were less common and absent respectively.
5. Heterospecific ovicide appears to explain the second-female advantage in competition between these species. Second-female advantage is contrary to the paradigmatic view of multiparasitism, where the first-ovipositing female has an advantage in competition or one of the species consistently prevails in competition.     

Seemingly maladaptive refraining from infanticidal probing at the third parasitism attack by the semi-solitary parasitoid Echthrodelphax fairchildii （Hymenoptera： Dryinidae）

We assessed the adaptiveness of refraining from infanticidal probing at the third attack under triple parasitism in the parasitoid Echthrodelphaxfairchildii Perkins, by comparing fitness returns from the third attack with and without probing. Fitness returns were assessed in terms of the survival rate, mean developmental time, and mean adult head width of the progenies. Not probing was maladaptive under triple parasitism with oviposition intervals of 1/24 and 24/24 hours （where the numbers before and after the slash refer to the first-to-second and second-to-third oviposition intervals, respectively）, although no significant difference was detected in fitness returns for oviposition intervals of 24/1 hours. We suggest that the cost of probing （especially the decrease in the chance of future ovipositions） is a reason for the seemingly maladaptive absence of probing.     

Sex Allocation Decision Under Superparasitism by the Parasitoid Wasp Eupelmus vuilleti

Superparasitism is a widespread phenomenon in parasitoids and may be advantageous in some circumstances. In this study, offspring sex ratio was analysed in three superparasitism situations: when the second egg was laid by a random Eupelmus vuilleti (Hymenoptera: Eupelmidae) female from a group, when an isolated female was allowed to lay two eggs on the same host (self-superparasitism) or laid one egg on a host already parasitized by a conspecific (conspecific superparasitism). Females produced a different offspring sex ratio according to the different superparasitism situations tested. These sex ratios are in line with the local mate competition theory. The results further suggest that females can discriminate between hosts parasitized by a conspecific or by themselves and adapt the sex of the eggs they lay accordingly.     

Superparasitism strategies by a native and an exotic parasitoid species attacking the Mexican fruit fly,Anastrepha ludens (Diptera: Tephritidae)

Superparasitism refers to the action of parasitoids ovipositing eggs in hosts that are already parasitized; this inevitably results in the elimination of supernumerary larvae in solitary parasitoids. Here, we investigated superparasitism performed by two species of solitary parasitoids on the larvae of Anastrepha ludens (Loew; Diptera: Tephritidae): a native species, Doryctobracon crawfordi (Viereck; Hymenoptera: Braconidae), and an exotic species, Diachasmimorpha tryoni (Cameron; Hymenoptera: Braconidae). Tests were conducted under laboratory conditions evaluating the behaviour of females acting alone (self-superparasitism) or in groups (conspecific superparasitism). Parasitism strategies were different between these two species. In D. crawfordi, the number of first instar larvae found in each dissected host pupa was never greater than two, regardless of the number of oviposition scars observed per pupa. In contrast, there was a positive correlation between the number of oviposition scars and the number of first instar larvae in D. tryoni. The survival and fecundity of D. crawfordi females emerging from pupae with one scar was higher than in females emerging from pupae with more scars. In D. tryoni, the number of oviposition scars did not show deleterious effects on life history traits and was positively correlated with the proportion of emerging females. An understanding of the superparasitism strategy adopted by parasitoid species could be of great interest to augmentative biological control programmes because the mass rearing of natural enemies could be negatively or positively affected by this condition.     

Impact of superparasitism time intervals on progeny survival and fitness of an egg parasitoid

1.Superparasitism influences the fitness of female parasitoids and their progeny, and increasing time interval between oviposition bouts generally reduces survival probabilities of the second clutch. However, the timing of superparasitism may, under certain conditions, favour the second clutch. 2. This study investigated the effects of superparasitism time intervals on survival and fitness of both clutches, allowing the egg parasitoid Trichogramma euproctidis to parasitise previously parasitised Ephestia kuehniella host eggs at different time intervals. 3. In short intervals (0–1 h), a significant advantage was found for the second clutch over the first clutch (93.1% survival). In contrast, the second clutch was outcompeted by the first clutch in 17–19 h and 27–29 h intervals. Females deposited their eggs into larvae (intraspecific hyperparasitism) in a 39–41 h interval with a probability of survival of 57.1%. Females mostly refused to hyperparasitise pupae (～80% rejection at 124–126 h), and when they did, their progeny never survived. 4. Hyperparasitism significantly increased parasitoid mortality in both clutches from less than 20% (superparasitism only) to over 35%. 5. Except on newly laid eggs (0–1 h), superparasiting females were frequently observed attempting to stab immatures of all stages (from 36.4% to 89.4% of all ovipositions depending on treatment), but infanticide only appeared to succeed on larvae (39–41 h). 6. When the second clutch survived, emerging parasitoids were smaller than control individuals, probably due to resource depletion. 7. These results suggest that T. euproctidis females can detect that a host has been previously parasitised but they cannot perceive superparasitism time intervals.     

Self and conspecific superparasitism by the egg parasitoid Trichogramma evanescens

Superparasitism is a widespread phenomenon in insect parasitoids and may be advantageous in certain circumstances. In this paper, we distinguish two kinds of superparasitism with different adaptive consequences for an ovipositing parasitoid: self superparasitism, where a parasitoid oviposits in a host in which she has previously oviposited, and conspecific superparasitism, where she oviposits in a host containing egg(s) from a previous oviposition by a conspecific. Our studies on Trichogramma evanescens Westwood show that females lay smaller clutches on parasitized than on healthy hosts but make the same overall allocation of males and females, although the sequence of sexes during oviposition differs. No difference was found between allocation in self and conspecific superparasitism. These results are discussed in the light of theories for progeny and sex allocation.

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Selbst- und konspezifisch-superparasitismus durch die schlupfwespe Trichogramma evanescens

Zusammenfassung Superparasitismus ist ein weitverbreitetes Phänomen in Parasitoiden von Insekten und es kann unter bestimmten Umständen vorteilhaft sein. Diese Arbeit macht Unterschied zwischen zwei Formen von Superparasitismus, jeder mit seiner eigenen adaptiven Konsequenz für die parasitierende Schlupfwespe: Selbst-Superparasitismus, wenn eine Schlupfwespe einen Wirt parasitiert die sie vorher selbst parasitiert hat, und Konspezifisch-Superparasitismus, wenn sie einen Wirt parasitiert die vorher von einem Artgenossen parasitiert worden ist. Unsere Untersuchungen an Trichogramma evanescens zeigen dass die Weibchen auf den belegten Wirten, aber das Gesamtverhältnis von männlichen und weiblichen Brut ist dasselbe, obschon die Reihenfolge in den die Eier der beiden Geschlechte abgelegt werden sich underscheiden. Keinen Unterschied wurde gefunden zwischen die Ablegung während elbst-Superparasitismus und Konspezifisch-Superparasitismus. Diese Ergebnisse werden diskutiert im Rahmen der Theorien für die Belegung des Wirtes in bezug auf die Anzahl und das Geschlecht der Eier.