Ecological Entomology (2009), 34, 652–662 DOI: 10.1111/j.1365-2311.2009.01115.x Sequences of sex allocation and mortality in clutches of Metaphycus parasitoids of soft scale insects and the prevalence of all-female broods APOSTOLOS KAPRANAS 1 , ERIC WAJNBERG 2 and ROBERT F. LUCK 1 1 Department of Entomology, University of California, Riverside, California, U.S.A. and 2 INRA, 400 Route des Chappes, BP 167, 06903 Sophia Antipolis Cedex, France Abstract. 1. In many gregarious or quasi-gregarious parasitoids that experience local mate competition, precise sex ratios with low variance are observed. Precise sex ratios can be achieved by laying male and female eggs in non-random sequences. 2. Developmental mortality can also alter sex ratios of emerging offspring, and subsequently influence sex ratio optima. 3. The present study investigates sex allocation by Metaphycus flavus Howard, M. luteolus Timberlake, and M. angustifrons Compere (Hymenoptera: Encyrtidae), endoparasitoids of soft scale insects, in the laboratory. 4. All three Metaphycus species had precise secondary sex ratios when parasitising brown soft scale, Coccus hesperidum, L. in the laboratory. Moreover, we documented that all three species lay fertilised (= female) eggs first followed by unfertilised (= male) eggs at the end of the oviposition bout. However, there were significant differences in sex allocation sequences among species. 5. Mortality rates of eggs allocated within an oviposition bout also varied con- siderably, indicating that there is a significant interspecific variation in sequence position-specific mortality. 6. Using a stochastic Monte Carlo simulation approach, we provide evidence that the incidence of all-female broods in these parasitoid wasps appears mainly due to developmental mortality and not due to decisions by the ovipositing female. In two species the prevalence of all-female broods was independent of clutch size, contrary to what is expected from theory. The influence of mortality on optimal sex allocation in these parasitoids is discussed. Key words. All-female broods, developmental mortality, encapsulation, Metaphycus , precise sex ratios, sex allocation sequence pattern, soft scale insects. Introduction In many parasitic Hymenoptera, mating is confined mostly among siblings, and is often restricted to a local area or natal patch instead of being panmictic (Godfray & Cook, 1997). Under this scenario of spatially-structured populations, males compete for mates. This is known as local mate competition and production of female-biased sex ratios is Correspondence: Apostolos Kapranas, Department of Plant Pro- duction, School of Agriculture, Technological Educational Institute, Larissa 41110, Greece E-mail: akapranas@gmail.com usually the optimal strategy for ovipositing females (Hamilton, 1967). Hamilton’s Theory of Local Mate Competition predicts that the optimum sex ratio for mothers depends on the number of colonists (foundresses) allocating offspring to a patch (Hamilton, 1967, 1979). When there are only a few foundresses in the patch, the optimal sex ratios are highly female-biased, thus reducing competition among males for mating opportunities. In extreme situations where only one female is allocating offspring in a patch, allocating more sons than is necessary to inseminate their sisters is a waste of host resources better provisioned for the production of daughters. In such a situation, the allocation of ‘precise sex ratios’ with  2009 The Authors 652 Journal compilation  2009 The Royal Entomological Society