David Damiens

Spermatogeny as a life-history index in parasitoid wasps.

Reproduction is a major life-history trait but it has been studied mostly in relation to female reproductive effort. Recently, an ovigeny index using the proportion of oocytes ready to be oviposited at eclosion has been proposed for female insect parasitoids. Here, we propose a spermatogeny index for male parasitoid wasps. Prospermatogenic species have an index of 1, have all their spermatozoids mature at emergence and do not produce more later in life. At the other end of the spectrum, synspermatogenic species have no spermatozoids at emergence and produce them later in life. The level of spermatogeny should be linked to several other life-history parameters such as longevity, size, nutrition, distribution of mating opportunities and dispersion before and after mating. Data presented for some parasitoid species support the presence of variability in this male life-history parameter.

Male reproductive strategy in Trichogramma evanescens: sperm production and allocation to females

Abstract.  The production and allocation of sperm among successive mates during a males life largely determine its fitness. The sperm production pattern and sperm allocation to females is studied in Trichogramma evanescens, a short‐lived egg parasitoid of several lepidopteran species. At emergence, virgin males have an average of 1607 ± 249 sperm stored in the seminal vesicles and no further production occurs during adult life. These males are able to mate with at least 20 females in rapid succession. During the first 10 matings, the males transfer approximately 100 sperm each time and then transfer fewer and fewer sperm per mating. The number of sperm stored in spermathecae of successively mated females remains relatively constant for the first 10 females, and decreases slowly for the subsequent females. The relationship between male reproductive strategy and some life‐history traits are discussed.

Qualitative aspects of sperm stock in males and females from Eupelmus orientalis and Dinarmus basalis (Hymenoptera: Chalcidoidea) as revealed by dual fluorescence

Abstract The quality of a sperm population can be characterized physiologically and its fecundity predicted by its viable : non‐viable sperm ratio. To improve the knowledge of reproductive strategies in two ectoparasitoid hymenopteran species, Eupelmus orientalis Crawford (Hymenoptera: Eupelmidae) and Dinarmus basalis Rondani (Hymenoptera: Pteromalidae), the assessment of sperm viability using the dual fluorescence staining procedure SYBR‐14 : propidium iodide was developed. The aim of the study was to provide a comparative test in vitro applicable to both sexes to study the evolution of sperm quality at various stages of the reproductive processes. The reliability of propidium iodide to detect non‐viable sperm (stained in red) was confirmed in both species on the basis of two stress tests (ethanol and Triton X‐100) but our study also revealed that propidium iodide concentrations must be adequately adjusted for each single species. This experiment also demonstrated the physiological heterogeneity of sperm populations in E. orientalis and D. basalis males and females. In both species, 40% of the sperm in the seminal vesicles was found to be non‐viable. By contrast with E. orientalis, the populations of non‐viable sperm estimated from the seminal vesicles of D. basalis were found to be strongly different from those observed in the spermatheca. From the present results, the population of viable sperm detected in the spermatheca of females from both species proved a reliable predictor of fertilization achieved in ovipositing females.

Male Mate Choice in Trichogramma Turkestanica

In most animals it is the sex that invests the most in reproduction, generally the female, that expresses mate choice. However, in numerous species, males or both males and females are choosy. We investigated mate choice in males of the egg parasitoid Trichogramma turkestanica Meyer (Hymenoptera: Trichogrammatidae). We tested the impact of age and feeding status of males on their capacity to choose between virgin or mated and kin or non-kin females. As expected, males showed no preference between kin and non-kin mates, but inseminated virgin females over mated ones. No effect of age on the level of choosiness was found, but unfed males were choosier than fed ones. This is the first study to show an effect of feeding status of males on mate choice in insect parasitoids.

Strategic ejaculation in the egg parasitoid Trichogramma turkestanica (Hymenoptera: Trichogrammatidae)

Abstract 1. Several parameters influence sperm allocation by males, including their size and sperm stock, intra‐specific variability, quality of females’, as well as the risk and intensity of sperm competition.

Male reproductive investment relative to age and flight behaviour in the monandrous butterfly Pararge aegeria

Male reproductive investment may signify a considerable cost to male insects that produce sperm packages or spermatophores. Male butterflies allocate much of their active time budget to mate location, and they may adopt different behavioural strategies to do so. In the speckled wood butterfly (Pararge aegeria L.), males adopt either a territorial wait-and-fight strategy (territorial perching) or a fly-and-search strategy in wider areas (patrolling). In this study, we analysed the impact of male age, male size and male behaviour (i.e. behavioural strategies and levels of activity) on spermatophore investment (i.e. spermatophore mass, number of eupyrene sperm bundles). As predicted, reproductive investment increased with male age and size. Nevertheless, the increase of spermatophore mass with age and the number of eupyrene sperm bundles (i.e. fertile sperm) was stronger in low-activity males compared to active flying males. This suggests that flight activity has a negative impact on male reproductive investment. However, males that were forced to fly in the laboratory produced more eupyrene sperm bundles than resting males. We discuss the potential effects of male–male competition and predation risk on current versus future male reproduction. Males adopting different mate-locating strategies (perching and patrolling) in outdoor cages did not differ in spermatophore traits as was predicted from their very different flight performances. Copulations of territorial perching males took somewhat longer than copulations with non-perching males. There was a significant family effect of spermatophore size and of the expression of male mate-locating strategies suggesting heritable variation. Female traits (i.e. age and size) did not strongly affect spermatophore production. We discuss the results relative to both ultimate and proximate explanations of the complex relationships between butterfly activity, behavioural strategies, age and spermatophore production.

Bad housekeeping: why do aphids leave their exuviae inside the colony?

BackgroundAnimals can gain protection against predators and parasites by living in groups. The encounter-dilution effect provides protection when the probability of detection of a group does not increase in proportion to group size (i.e. encounter effect), so that predators do not offset the encounter effect by attacking more members of the group (i.e. dilution effect). In this paper, we propose a novel mechanism by which prey insects could gain by producing decoys that act as multiple targets for predators or parasitoids if these decoys are recognised as preys or hosts and negatively affect the patch foraging strategy of these predators and parasitoids. Such a decoy mechanism could be present in aphid colonies in which aphid exuviae are recognised and attacked by Aphidiine wasps.ResultsWe conducted a behavioural study to evaluate the effect of exuviae on parasitoid patch residence time and egg allocation in experimental aphid patches with or without exuviae. We showed that exuviae are recognised and attacked at the same level as aphids when both are present in the patch. While parasitism rate was not significantly lower in patches with exuviae when the parasitoid left the patch, the time wasted by parasitoids to handle exuviae did influence the patch residence time. As a consequence, the attack rate on the live aphids was lower in patches that contain exuviae.ConclusionAphids had more time available to flee and thus each individual might gain protection against parasitoids by leaving their exuviae near and within the colony. These results demonstrate that the encounter-dilution effect provided by living in a group can be enhanced by extra-materials that act as decoy for natural enemies.

Comparison of reproductive traits of regular and irradiated male desert locust Schistocerca gregaria (Orthoptera: Acrididae): Evidence of last-male sperm precedence

Summary The sterile insect technique (SIT) is increasingly used to control pest insect populations. The success of SIT control programs depends on the ability to release sterile males and on the capacity of sterile males to compete with wild males to inseminate wild females. In this study, we evaluated the mating performance of Schistocerca gregaria (Försk.) males irradiated with 4 Gray. We compared reproductive traits, such as duration of precopulation time, mating duration, quantity of sperm stored by females after copulation, number of females mated successively and postmating competition of irradiated males with non-irradiated males. Irradiated males were able to mate but the resulting number of offspring was dramatically reduced compared to the average number of offspring observed during a regular mating. During a single copulation, irradiated males transferred fewer sperm than regular males but, theoretically, this quantity is enough to fertilize all the eggs produced by a female during its reproductive life. Irradiated males also had the ability to remove sperm from a previous mating with unirraditated males. This new information on the mating strategies helps explain the post-copulation guarding behaviour of S. gregaria.