Sex allocation and the evolution of insemination capacity under local mate competition

Local mate competition (LMC) theory has proved enormously successful in predicting sex ratios across a broad range of organisms when localised mating patches lead to mating competition amongst kin. As such, LMC is a key component of sex allocation theory. However, the mating systems that influence and promote LMC also shape other traits, as well as sex allocation. These aspects of LMC mating systems have received far less attention, including in species where LMC is common, such as parasitoid wasps. Here, we consider how LMC influences the evolution of insemination capacity in parasitoids, a key reproductive allocation decision for males that should be under both natural and sexual selection. Basic LMC theory predicts that a single female exploiting a patch should produce just enough sons to inseminate all her daughters, that is, between them these sons should have sufficient insemination capacity to inseminate their sisters. However, the insemination capacity of males is generally higher than predicted and, in order to classify parasitoid species, we propose an Index of Insemination Strategy (IIS): the ratio between the insemination capacity of males on the emergence patch and the average number of females available per male at emergence on that patch. A survey of IIS for 25 species belonging to 10 hymenopteran families showed that IIS values ranged from 0.9 to 40.9, supporting the idea that males typically have more sperm than predicted. Several factors could explain these high IIS values, including non-local mating, temporal variation in emergence, variation in mate acquisition capacity, the intensity of sperm competition, and responses to host quality

Sex allocation and the evolution of insemination capacity under local mate competition

RAB is supported by a NERC DTG studentship.Local mate competition (LMC) theory has proved enormously successful in predicting sex ratios across a broad range of organisms when localised mating patches lead to mating competition amongst kin. As such, LMC is a key component of sex allocation theory. However, the mating systems that influence and promote LMC also shape other traits, as well as sex allocation. These aspects of LMC mating systems have received far less attention, including in species where LMC is common, such as parasitoid wasps. Here, we consider how LMC influences the evolution of insemination capacity in parasitoids, a key reproductive allocation decision for males that should be under both natural and sexual selection. Basic LMC theory predicts that a single female exploiting a patch should produce just enough sons to inseminate all her daughters, that is, between them these sons should have sufficient insemination capacity to inseminate their sisters. However, the insemination capacity of males is generally higher than predicted and, in order to classify parasitoid species, we propose an Index of Insemination Strategy (IIS): the ratio between the insemination capacity of males on the emergence patch and the average number of females available per male at emergence on that patch. A survey of IIS for 25 species belonging to 10 hymenopteran families showed that IIS values ranged from 0.9 to 40.9, supporting the idea that males typically have more sperm than predicted. Several factors could explain these high IIS values, including non-local mating, temporal variation in emergence, variation in mate acquisition capacity, the intensity of sperm competition, and responses to host quality.PostprintPeer reviewe

Standard operating procedures for standardized mass rearing of the dengue and chikungunya vectors Aedes aegypti and Aedes albopictus (Diptera: Culicidae) - I - egg quantification

BACKGROUND: Quantification of eggs prior to rearing the immature stages of mosquitoes is an essential step in establishing a standardized mass rearing system. To develop a simple and accurate method of egg quantification for Aedes aegypti and Aedes albopictus, the relationship between egg number and weight, as well as egg number and volume, were studied. METHODS: Known quantities of eggs (1,000, 3,000, 6,000, 12,000, 15,000, 18,000, 21,000 and 27,000) were counted and subsequently their weight and volume were measured. Best-fit curves and regression equations were used to describe relationships between Aedes egg number and both weight and volume. RESULTS: Eighteen thousand Ae. aegypti eggs weighed 159.8 mg and had a volume of 277.4 μl, compared to measurements of 131.5 mg and 230.3 μl for Ae. albopictus. The eggs of Ae. aegypti were thus larger and heavier than those of Ae. albopictus. The use of weight and volume to quantify egg number was validated by counting volumes and weights of eggs expected to correspond to 3,000 and 18,000 eggs of each species; significant correlations were found in all cases except in the case of 3,000 Ae. albopictus eggs measured by volume. CONCLUSION: Methods for egg quantification were validated and shown to be a consistent and practical means to achieve uniform distribution of Aedes larvae between rearing trays, important for optimal mass rearing of the immature stages of Aedes mosquitoes

Standard operating procedures for standardized mass rearing of the dengue and chikungunya vectors Aedes aegypti and Aedes albopictus (Diptera: Culicidae) - II - Egg storage and hatching

Abstract Background Management of large quantities of eggs will be a crucial aspect of the efficient and sustainable mass production of mosquitoes for programmes with a Sterile Insect Technique component. The efficiency of different hatching media and effectiveness of long term storage methods are presented here. Methods The effect on hatch rate of storage duration and three hatching media was analysed: deionized water, boiled deionized water and a bacterial broth, using Two-way ANOVA and Post hoc Tukey tests, and the Pearson correlation coefficient was used to find the effect on the proportion of collapsed eggs. Two long term storage methods were also tested: conventional storage (egg paper strips stored in zip lock bags within a sealed plastic box), and water storage (egg papers in a covered plastic cup with deionized water). Regression analyses were used to find the effect of water storage and storage duration on hatch rate. Results Both species hatched most efficiently in bacterial broth. Few eggs hatched in deionized water, and pre-boiling the water increased the hatch rate of Ae. aegypti, but not Ae. albopictus. A hatch rate greater than 80 % was obtained after 10 weeks of conventional storage in Ae. aegypti and 11 weeks in Ae. albopictus. After this period, hatching decreased dramatically; no eggs hatched after 24 weeks. Storing eggs in water produced an 85 % hatch rate after 5 months in both species. A small but significant proportion of eggs hatched in the water, probably due to combined effects of natural deoxygenation of the water over time and the natural instalment hatching typical of the species. Conclusions The demonstrated efficiency of the bacterial broth hatching medium for both Ae. albopictus and Ae. aegypti facilitates mass production of these two important vector species in the same facility, with use of a common hatching medium reducing cost and operational complexity. Similarly the increased hatch rate of eggs stored in water would allow greater flexibility of egg management in a large programme over the medium term, particularly if oxygenation of the water by bubbling oxygen through the storage tray could be applied to prevent hatching during storage

Laboratory evaluation of the effects of sterilizing doses of gamma-rays from Caesium-137 source on the daily flight activity and flight performance of Aedes albopictus males

The control of Aedes albopictus through Sterile Male Releases requires that the most competitive males be mass-reared and sterilized usually with gamma- or X-ray radiation prior to release. Developing an understanding of the impact of irradiation treatment on flight performance in sterile males is very important because any fitness cost may reduce the efficacy of SIT intervention in the field. Here, we examined the role of irradiation exposure and sugar-feeding on daily flight activity and performance of Ae. albopictus males sterilized during pupal stage with gamma-radiation at 35Gray from a Caesium 137 source. We used a previously developed automated video tracking system to monitor the flight activity of different groups of sterile and control non-sterile males over 24 hours in a flight arena. This monitoring took place under controlled laboratory conditions and we wished to quantify the daily flight activity and to highlight any changes due to radiation treatment and nutritional conditions (starved versus sugar fed). Our experimental evidence demonstrated a characteristic diurnal flight activity with a bimodal pattern regardless of the treatment. Precisely, both irradiated and non-irradiated males exhibited two distinct peaks in flight activity in the morning (6-8 a.m.) and late afternoon (4-6 p.m.). Under changing physiological conditions, irradiated males were generally more active over time and flew longer overall distances than control male populations. These results suggest some internal circadian control of the phase relation to the light-dark cycle, with evidence for modification of flight performance by nutritional status. The fact that daily activity patterns are alike in irradiated and control Ae. albopictus males, and that sterile males could display higher flight performance, is in contrast with the hypothesis that irradiation treatment appears to reduce the fitness of male mosquitoes. We discuss the implications of the present study in sterile-male release programs against Ae. albopictus