The invasive parasitic fly, Philornis downsi (Muscidae), is one of the greatest threats to the avifauna of the Galapagos Islands. The larvae of this fly feed on the blood and tissues of developing nestlings of at least 18 endemic and native birds. The aim of the current study was to investigate biotic and abiotic factors that may influence the population dynamics of this invasive parasite. To study the influence of vegetation zone and related climatic factors on fly numbers, a bi-weekly monitoring program using papaya-baited traps was carried out at a dry, lowland site and at a humid, highland site on Santa Cruz Island between 2012–2014. Female flies, a large proportion of which were inseminated and gravid, were collected throughout the year at both sites, indicating females were active during and between the bird breeding seasons. This is the first evidence that female flies are able to persist even when hosts are scarce. On the other hand, catch rates of male flies declined between bird breeding seasons. Overall, catch rates of P. downsi were higher in the drier, lowland habitat, which may be a consequence of host or resource availability. Time was a stronger predictor of adult fly numbers than climate, further suggesting that P. downsi does not appear to be limited by its environment, but rather by host availability. Seasonal catch rates suggested that populations in both habitats were continuous and multivoltine. Numbers of adult female flies appeared to be regulated chiefly by simple direct density dependence, and may be governed by availability of bird nests with nestlings. Nevertheless, confounding factors such as the existence of reservoir hosts that perpetuate fly populations and changes in behavior of P. downsi may increase the vulnerability of bird hosts that are already IUCN red-listed or in decline.

Despite the diverse array of mating systems and life histories which characterise the parasitic Hymenoptera, sexual selection and sexual conflict in this taxon have been somewhat overlooked. For instance, parasitoid mating systems have typically been studied in terms of how mating structure affects sex allocation. In the past decade, however, some studies have sought to address sexual selection in the parasitoid wasps more explicitly and found that, despite the lack of obvious secondary sexual traits, sexual selection has the potential to shape a range of aspects of parasitoid reproductive behaviour and ecology. Moreover, various characteristics fundamental to the parasitoid way of life may provide innovative new ways to investigate different processes of sexual selection. The overall aim of this review therefore is to re-examine parasitoid biology with sexual selection in mind, for both parasitoid biologists and also researchers interested in sexual selection and the evolution of mating systems more generally. We will consider aspects of particular relevance that have already been well studied including local mating structure, sex allocation and sperm depletion. We go on to review what we already know about sexual selection in the parasitoid wasps and highlight areas which may prove fruitful for further investigation. In particular, sperm depletion and the costs of inbreeding under chromosomal sex determination provide novel opportunities for testing the role of direct and indirect benefits for the evolution of mate choice.

The neotropical parasitoid Conura annulifera (Walker) (Hymenoptera: Chalcididae) is known to parasitize birdparasitic flies in the genus Philornis (Diptera: Muscidae) including P. downsi (Dodge and Aitken), a species that has invaded the Gal apagos islands and is negatively impacting populations of Darwin's finches. We report here some aspects of the life history, field ecology, and host specificity of C. annulifera. We collected puparia of four Philornis species in 13 bird nests during 2015 and 2016 in western mainland Ecuador and found that C. annulifera and three other parasitoid species emerged from those puparia. This is the first record of C. annulifera in Ecuador. Rearing records and dissections of parasitized puparia revealed that C. annulifera is a solitary pupal ectoparasitoid, placing its eggs in the gap between host pupa and puparium. Laboratory studies of host specificity involving P. downsi and pupae from five other dipteran, three lepidopteran, and one hymenopteran species found that C. annulifera only produced progeny when presented with P. downsi pupae. Pupae of P. downsi that had been exposed to C. annulifera also failed to emerge more often than expected by chance compared with no-parasitoid controls, suggesting that the parasitoids can cause developmental mortality through means other than successful parasitism. These studies constitute the first steps in evaluating C. annulifera as a potential biological control agent of P. downsi in the Gal apagos Islands.

The taxonomically widespread nature of polyandry remains a puzzle. Much of the empirical work regarding the costs and benefits of multiple mating to females has, for obvious reasons, relied on species that are already highly polyandrous. However, this makes it difficult to separate the processes that maintain the current level of polyandry from the processes that facilitate its expression and initiated its evolution. Here we consider the costs and benefits of polyandry in Nasonia vitripennis, a species of parasitoid wasp that is “mostly monandrous” in the wild, but which evolves polyandry under laboratory culture conditions. In a series of six experiments, we show that females gain a direct fecundity and longevity benefit from mating multiply with virgin males. Conversely, mating multiply with previously mated males actually results in a fecundity cost. Sexual harassment may also represent a significant cost of reproduction. Harassment was, however, only costly during oviposition, resulting in reduced fecundity, longevity, and disrupted sex allocation. Our results show that ecological changes, in our case associated with differences in the local mating structure in the laboratory can alter the costs and benefits of mating and harassment and potentially lead to shifts in mating patterns.

In the last two decades molecular techniques have revealed that polyandry, or multiple mating by females with different males, is common. One explanation is that females engage in convenience polyandry, mating multiply to reduce the costs of sexual harassment. Although the underlying logic of convenience polyandry is clear, and harassment often seems to influence mating outcomes, it has not been subjected to as thorough theoretical or empirical attention as other explanations for polyandry. Here, we reexamine convenience polyandry in the light of a new generation of studies showing previously unconsidered benefits of polyandry. We suggest that true convenience polyandry is likely to be a fleeting phenomenon, but a phenomenon that can profoundly shape mating system evolution due to potential feedback loops between resistance to males and the costs and benefits of mating. The history of polyandry Mating systems are often classified as either monogamous, with a single male paired with a single female, or polygamous, with multiple mates of one or the other sex. Polygamy in turn can be subdivided into polygyny (one male with multiple females) or polyandry (one female with multiple males; see glossary). The near ubiquitous nature of polygyny has never been debated, but polyandry has had a somewhat contradictory history. On the one hand, researchers using insects and other invertebrates as study organisms have often acknowledged the prevalence of