Robert W. Matthews

Courtship in Parasitic Wasps

Courtship may be defined as any behaviors between conspecific individuals of opposite sex which facilitate mating. Such behaviors, with their incredible variety and obvious importance, have provided biologists with a vast and fascinating field of study. The evolution of such systems has, in particular, received considerable attention in recent years. For the vertebrates, this area has been capably reviewed by Orians (1969) and Trivers (1972).

Biology of the Parasitoid Melittobia (Hymenoptera: Eulophidae)*

As parasitoids upon solitary bees and wasps and their nest cohabitants, Melittobia have an intricate life history that involves both female cooperation and variably expressed male siblicidal conflict. Inter- and intrasexual dimorphism includes blind, flightless males and (probably nutritionally determined) short- and long-winged females. Thought to be highly inbred, Melittobia do not conform to local mate competition (LMC) theory but exhibit simple forms of many social insect traits, including overlapping adult generations, different female phenotypes, close kinship ties, parental care, and altruistic cooperative escape behaviors. Most host records and research findings are based on only 3 species--M. acasta, M. australica, and M. digitata--but any of the 12 species could have pest potential due to their polyphagy, explosive population growth, cryptic habits, and behavioral plasticity. Readily cultured in the laboratory, Melittobia offer considerable potential as a model for genetic, developmental, and behavioral studies.

Hierarchical genetic structure of the introduced wasp Vespula germanica in Australia

The wasp Vespula germanica is a highly successful invasive pest. This study examined the population genetic structure of V. germanica in its introduced range in Australia. We sampled 1320 workers and 376 males from 141 nests obtained from three widely separated geographical areas on the Australian mainland and one on the island of Tasmania. The genotypes of all wasps were assayed at three polymorphic DNA microsatellite markers. Our analyses uncovered significant allelic differentiation among all four V. germanica populations. Pairwise estimates of genetic divergence between populations agreed with the results of a model‐based clustering algorithm which indicated that the Tasmanian population was particularly distinct from the other populations. Within‐population analyses revealed that genetic similarity declined with spatial distance, indicating that wasps from nests separated by more than ~25 km belonged to separate mating pools. We suggest that the observed genetic patterns resulted from frequent bottlenecks experienced by the V. germanica populations during their colonization of Australia.

Mating and reproduction in the wasp Vespula germanica

Abstract. We used polymorphic microsatellite markers to study patterns of queen and worker reproduction in annual nests of the wasp Vespula germanica in its introduced range in Australia. We found that queens were typically polyandrous (at least 85.4% mated multiply), with the minimum number of male mates ranging from 1 to 7. Calculations based on nestmate worker relatedness (r=0.46) yielded an estimate of effective queen mating frequency of 2.35. Queens were unrelated to their mates (r=–0.01), indicating that mating occurred at random within Australian V. germanica populations. In addition, the distribution of the minimum number of male mates of queens followed a Poisson distribution. This result suggested that the probability of a queen remating was not affected by previous copulations. We also discovered that mates of polyandrous queens contributed unequally to progeny production leading to significant male reproductive skew within nests. Analyses of nestmate male genotypes revealed that queens usually produced most or all males. However, workers were responsible for the production of many males in a few nests, and, in contrast to theoretical expectations, two of these nests were apparently queenright.

Offspring production and development in the parasitoid wasp Melittobia clavicornis (Cameron) (Hymenoptera: Eulophidae) from Japan

The development time, sex ratio and offspring production of Melittobia clavicornis reared with wild, facultative and factitious hosts are presented. Known hosts and different biological aspects presented in previously published reports are summarized and clarified. Immature development time was equivalent or slightly longer than that of other Melittobia species, and the sex ratio was approximately 97% female. Total offspring numbers were considerably lower than that of other Melittobia species using the same hosts. We report female dimorphism in this species for the first time. The number and relative proportion of brachypterous morph females produced was higher than that in other species of the genus.

Trans-bergamotenes-male pheromone of the ectoparasitoid Melittobia digitata.

The first male-produced sex attractant pheromone in the parasitic Hymenoptera has been identified. The elaborate courtship behavior of Melittobia digitata, an idiobiont that parasitizes the last larval instar or the pupal stage of solitary bees and wasps, involves a series of coordinated movements of legs, wings, and antennae, initiated after the female is attracted to the blind, flightless male. We identified α- and β-trans-bergamotene as the active compounds of the male M. digitata sex attractant. Variation in the release of the sex pheromone by males and the pheromone load during aging is also described.

Population Genetic Structure and Social Evolution in the Sphecid Wasp Microstigmus comes

Genetic structure and sex allocation were studied in a natural population of the primitively eusocial sphecid wasp Microstigmus comes. No higher-level genetic structure was discernible at the level of the subpopulation, and microgeographic structure at the level of the local deme or individual host palm was, at most, modest. In contrast, genetic structure at the level of the individual nest was striking, with the average genetic relatedness among female nest mates estimated to be 0.62-0.67. This high relatedness results from the fact that colonies comprise relatively simple families, which are, in many instances, matrifilial monogynous societies. High relatedness among female nest mates and the absence of conspicuous higher-level structure, in conjunction with the observed female-biased sexinvestment ratios, are compatible with the interpretation that kin selection has played a major role in the origin of eusocial behavior in the recent ancestors of this wasp. The inferred colony composition and social organization further suggest that this social evolution may have occurred via a subsocial route, with simple matrifilial families rather than polygynous groups serving as the principal setting for the development of worker altruism.

Development of Melittobia australica Girault and M. digitata Dahms (Parker) (Hymenoptera: Eulophidae) parasitizing Neobellieria bullata (Parker) (Diptera: Sarcophagidae) puparia

O desenvolvimento de Melittobia australica Girault e M. digitata Dahms parasitando puparios de Neobellieria (=Sarcophaga) bullata (Parker) foram estudados com densidades de um a cinco parasitoides femeas por pupario. Aspectos da biologia dos parasitoides tais como: numero de descendentes produzidos, longevidade, e tamanho do corpo dos descendentes, podem ser afetados em funcao do numero de parasitoides por pupario. Em geral, a porcentagem de puparios parasitados foi maior para M. digitata do que para M. australica. Independentemente da densidade de parasitoides por pupario, o numero total de descendentes produzidos foi significativamente maior para M. digitata (66,5 a 158,0)que para M. australica (10,9 a 55,5). Para ambas especies, o numero de descendentes produzidos por femea dos parasitoides foi inversamente proporcional a densidade dos parasitoides. O aumento da densidade dos parasitoides prolongou o tempo de desenvolvimento M. australica, e ocasionou reducao em M. digitata. A longevidade dos adultos emergidos de M. australica e M. digitata foi maior quando oriundos das densidades ate tres parasitoides por pupario, e o tamanho do corpo dos decendentes, mostrou significante reducao quando aumentou a densidade de femeas dos parasitoides por pupario. Entretanto, a razao sexual dos descendentes nao foi afetada, variando de 0,95 a 0,98 para M. australica, e de 0,95 a 0,97 para M. digitata. Os resultados mostram que M. digitata apresentou melhor desempenho que M. australica parasitando N. bullata, e ambas especies apresentaram reducao no desempenho aumentando a densidade de parasitoides por hospedeiro, sugerindo haver competicao entre os descendentes.

A SEX PHEROMONE IN MALES OF MELITTOBIA AUSTRALICA AND M. FEMORATA (HYMENOPTERA: EULOPHIDAE)

A 4-choice arena was used to test for evidence of a volatile male-produced attractant in macropterous and brachypterous forms of 2 closely related parasitic wasps, Melittobia australica Girault and M. femorata Dahms. Virgin females of both species and forms were strongly attracted to freshly killed mashed and intact males and to living males. They were unresponsive toward males which had been dead for at least 5 days and toward empty controls. Mated females were indifferent to males, regardless of male condition. Bioassays implicated the abdomen as the source of the male sex pheromone in both species.

Sexual behavior among parasitic Megarhyssa wasps (Hymenoptera: Ichneumonidae)

SummaryMale wasps of three sympatric species of Nearctic Megarhyssa (Hymenoptera: Ichneumonidae) typically form mixed-species (61.7%) aggregations composed of up to 28 males over sites of female emergence. Observations of 107 aggregations over two seasons in New York state revealed two male mating strategies: postemergence copulation on the tree surface and preemergence insemination accomplished by male abdominal insertion into the female emergence hole. Insertions by one or more males (as many as ten consecutively but not more than two simultaneously) occurred at 88% of the aggregations, with each inserting for an average of 24.8 min. Insemination as a result of preemergence insertion had a success rate of 83% while postemergence copulation attempts were successful 30% of the time (average duration 61.9 s). Individual male reproductive success was very low and not correlated with size, arrival order at emergence sites, or tenacity at the site. Males frequently aggregated at sites of male emergences as well as those of nonconspecifics, though conspecifics to the emerger ultimately played the major role at aggregations. Male-male aggression in aggregations was not apparent, though jostling occurred during the insertion period and during postemergence copulation attempts.