Levels Of Superparasitism Research Articles

An asexual strain of Lysiphlebus fabarum (Hymenoptera: Braconidae) gains fitness in superparasitised hosts, but a sexual strain pays costs

1. The fitness impacts of two levels of superparasitism were compared in a sexual and an asexual strain of Lysiphlebus fabarum (Marshall) developing in black bean aphids.2. Asexual females were larger than sexuals, had higher eggs loads, and better adult emergence in two of three treatments, but parasitised fewer available aphids in 24 h (80% fewer when foraging alone).3. Superparasitism resulted in wasps that were larger than those emerging from singly parasitised aphids, and asexual females had larger ovaries, without delayed development. In contrast, sexual wasps took about 2 days longer to develop in superparasitised hosts, and females had smaller ovaries with lower egg loads.4. The growth of host aphids bearing asexual larvae was not reduced relative to healthy aphids, except when heavily superparasitised, whereas sexual larvae reduced aphid growth in all treatments.5. Elimination of supernumerary larvae was virtually complete at 4.5 days after parasitism by sexual females, but no elimination occurred among asexual larvae. The evolution of diminished aggression in asexual larvae may be facilitated by greater genetic similarity, without necessarily leading to gregarious development, assuming the extended life of supernumeraries somehow improves survivor fitness.6. Sons of virgin sexual females developed faster than sons of mated females, implicating parental effects that slowed development of the latter.7. It is concluded that asexual females of this strain use superparasitism to improve host quality, and thus the fitness of their daughters, whereas females of the sexual strain prioritise offspring number.

Superparasitism in Laboratory rearing ofSpalangia cameroni(Hymenoptera: Pteromalidae), a parasitoid of medfly (Diptera: Tephritidae)

The frequency of superparasitism and its effects on the quality of laboratory-reared Spalangia cameroni (Hymenoptera: Pteromalidae) parasitoids were investigated under laboratory conditions. Numerous variables were measured, such as the number of 'ovip holes' per host as a measure of superparasitism. Adult emergence and sex ratio, as well as female size, emergence ability from soil and longevity were also measured. Finally, an assessment was made of fertility and survival of adult parasitoids emerging from the medfly Ceratitis capitata (Diptera: Tephritidae) pupae with different levels of superparasitism. A high frequency and prevalence of superparasitism under laboratory rearing conditions was observed. The number of 'ovip holes' per host ranged from one to 17, with an average (±SD) of 2.8±3.4. Sex ratios became increasingly female-biased with increasing levels of superparasitism, although overall levels of wasp emergence (male, female) declined. Nevertheless, no relationship was discerned between female size and level of superparasitism. The 'emergence ability from the soil' was higher in those parasitoids that emerged from strongly superparasitized hosts, but not related to the type of substrate in which the host pupae were buried. The level of superparasitism did not have a significant effect on the longevity, fertility and survival of female parasitoids. Our results support the hypothesis that superparasitism in S. cameroni might be adaptive, since attributes such as 'emergence ability from the soil', longevity, fertility and survival were not affected by the level of superparasitism or the presumably detrimental effects derived from physical combats among conspecific larvae. Our findings are relevant to recommendations for rearing S. cameroni for biological control releases, as well as shedding light on superparasitism under both laboratory and field conditions.

Using superparasitism by a stem borer parasitoid to infer a host refuge

Abstract. 1. Macrocentrus cingulum Reinhard (Hymenoptera: Braconidae), a parasitoid of the European corn borer, Ostrinia nubilalis, and the Asian corn borer, O. furnacalis (Lepidoptera: Pyralidae), has high fecundity but has been reported to parasitize a low proportion of host larvae. This was corroborated in field collections: in Hebei (China) and Delaware (U.S.A.), M. cingulum parasitized only 15 and 25%, respectively, of hosts collected.2. Because M. cingulum females cannot oviposit through plant tissue, they must parasitize hosts either before they have bored into stalks or while they are near entrance holes, so that at any one time, many Ostrinia larvae may be unavailable to M. cingulum. This refuge, together with fluctuations in abundance of foraging M. cingulum females, may explain why M. cingulum parasitizes relatively few Ostrinia larvae.3. To test this hypothesis, levels of superparasitism were measured in the field. Low parasitism resulting from a refuge for host larvae should cause high rates of superparasitism in hosts outside the refuge.4. Because M. cingulum is polyembryonic, the number of parasitoids per host does not indicate the level of superparasitism. Random amplified polymorphic DNA markers were used to determine the number of different genotypes emerging from each host. The resulting frequency distributions were fitted to those expected under random oviposition to estimate the proportion of Ostrinia larvae unavailable to M. cingulum.5. In the samples from Hebei and Delaware, the level of superparasitism was much higher than expected by chance if all hosts were available. Fitting the frequencies of genotypes per host to a Poisson distribution, the authors estimated that 74–82% and 69–74% of host larvae were unavailable to M. cingulum in these collections, respectively. This means that M. cingulum parasitized 60–84% and 82–95% of available hosts in these collections, respectively. These levels of parasitism contrast strongly with the 15–25% found when all hosts were assumed available for oviposition.6. Genetic distances of M. cingulum within and between hosts did not differ, allowing rejection of the hypothesis that high levels of superparasitism resulted from a female laying several eggs in the same host.7. The hypothesis that M. cingulum parasitizes few Ostrinia larvae because many larvae are in a refuge explains these data and previously published information better than other hypotheses that have been suggested.

Host-searching behavior ofVenturia canescens (Grav.) (Hymenoptera: Ichneumonidae): Superparasitism

The foraging behavior ofVenturia canescens, a solitary endoparasitoid of lepidopteran larvae, was investigated in the laboratory. FemaleVenturia canescens with a larger number of mature eggs to lay were found to have higher levels of superparasitism (measured as numbers of eggs laid per parasitized host). Increased parasitoid density was found to result in reduced levels of superparasitism by host-deprived (i.e.,undepleted) wasps. Females which had been allowed access to hosts before the experiment (depleted wasps) laid fewer eggs per parasitized host than undepleted wasps, although there was no significant difference in the levels of superparasitism among the depletion periods of 1, 2, 5, and 7 h. It was also found that an egg which was encountered less than 15 min after oviposition was much less likely to be avoided than one which was encountered after more than 15 min had elapsed.

SEX RATIO VARIATION IN A PARASITIC WASP I. REACTION NORMS.

To understand genetic and phenotypic constraints on the sex ratio in a parasitic wasp that attacks fly pupae, I carried out a laboratory study of sex ratio variability in five strains of Muscidifurax raptor (Hymenoptera: Pteromalidae). I manipulated the environment through combinations of temperature and day length, and the numbers of females that attack a group of hosts. The change of phenotype in each strain over the range of environmental conditions describes the norm of each reaction for that strain, and measures how a strain responds to environmental variation to create phenotypic variability. Sex ratio in parasitic wasps is a complex trait that has several components-the numbers of eggs laid by an ovipositing wasp and the fraction of eggs that are fertilized (female). Further, sex ratio may be influenced by a female's reaction to other females exploiting the same hosts (superparasitism). I found no strain-environment interactions in either sex ratio or fecundity when I varied environmental conditions. Although strains differed in sex ratio and fecundity, all strains produced a more female-biased sex ratio and had higher fecundity when temperature and day length increased. Sex ratio and fecundity were phenotypically correlated, and strains with greater fecundity also produced a more female-biased sex ratio. All strains facultatively shifted sex ratio toward a higher fraction of males with increasing female density, despite apparent differences in superparasitism among strains. Males and females survived equally during development, so that mortality differences among strains and across environments could not account for sex ratio variability. This study indicates that sex ratio variability among strains is constrained by the correlation between sex ratio and fecundity, and that strains display similar facultative shifts in sex ratio as female density increases because sex ratio shifts are insensitive to differing levels of superparasitism.

Observations on superparasitism in a natural population ofCentrodora scolypopae(Hymenoptera: Aphelinidae)

Superparasitism was found to be an important mortality factor in a natural population of Centrodora scolypopae (Valentine), parasitising the eggs of Scolypopa australis. Levels of superparasitism varied between years and host plants. Progeny from the first oviposition suppressed the development of later individuals. Centrodora scolypopae females were shown to discriminate for oviposition sites between parasitised and nonparasitised eggs.

Adaptive Superparasitism and Patch Time Allocation in Solitary Parasitoids: Searching in Groups vs Sequential Patch Visits

A deterministic ESS model was made to predict optimal degrees of superparasitism, when solitary parasitoids exploit a patch simultaneously or sequentially. Some predictions of this model are: (1) increasing levels of superparasitism and (2) longer patch times (measured as the sum of search times of all females visiting a patch) with increasing numbers of females visiting the patch. (3) More superparasitism and (4) longer patch times were predicted when females visited a patch simultaneously than when the same number of females visited a patch sequentially

Development of Microplitis rufiventris (Hymenoptera: Braconidae) in Superparasitized Spodoptera littoralis (Lepidoptera: Noctuidae)

The developmental history of Microplitis rufiventris Kokujev the parasite within singly parasitized hosts, Spodoptera littoralis (Boisduval), was compared with that in superparasitized hosts. Different levels of superparasitism had no effect on the length of the egg stage but caused changes in the lengths of the stadia of the surviving parasite and in the encapsulation ability of the host against the eliminated first-instar parasite. Larval development was faster in singly parasitized hosts and decreased with increasing superparasitism. The percentage of encapsulation of eliminated parasite larvae increased with increasing numbers of parasite progeny per host larva. The results suggest the existence of permanent and impermanent capsules, the latter detectable within heavily superparasitized hosts. Some of the surplus parasite progeny appear to be eliminated early by physiological suppression and others later by encapsulation. In singly parasitized hosts, a nontrivial number of parasite larvae died very early as a result of unspecified host immune response(s).

Intraspecific competition among first instars of the parasitic wasp Biosteres longicaudatus.

Females of the solitary endoparasitic wasp Biosteres longicaudatus sometimes deposit >1 egg (superparasitism) in each larva of the Caribbean fruit fly host, Anastrepha suspensa. As host density increases, there is an inverse relationship between the level of superparasitism and the number of progeny produced/female. Larval parasitoid competition in superparasitized hosts causes an abrupt decline from >1 to 1 or <1 parasitoid/host 24-36 h before the surviving parasitoid larva molts to the 2nd instar. The mechanism by which supernumaries are eliminated was investigated by indirect, in vivo and direct, in vitro methods. There is no apparent competition between parasitoid eggs of the same age. Parasitoid first instars utilize their heavily sclerotized mandibles to eliminate competitors, some of which are subsequently encapsulated by the host. First instars in vitro produce a substance that kills conspecifics. Presumably, this substance is secreted into the surrounding medium. One of each pair of parasitoid first instars, evenly matched for age and size, may live up to 6.4 days longer and grow to 0.13 mm larger than the other. Thus, B. longicaudatus, like other solitary endoparasitoids eliminates competitors by both combat and interference competitions. The latter case, presumably involves allelochemical toxins against conspecifics in the absence of physical encounter.