Mixed sex allocation strategies in a parasitoid wasp

Abstract

The sex allocation strategy of the parasitoid Laelius pedatus (Hymenoptera: Bethylidae) on different-sized hosts was investigated. The wasp lays from one to five eggs, and clutch size increases with host size. On the smallest hosts, single male eggs are laid, while on slightly larger hosts single female eggs are laid. On still larger hosts, gregarious clutches are laid which nearly always consist of a single male and one or more female eggs. The sex ratio strategy of the wasp appears to be influenced by a combination of local mate competition and conditional sex expression based on host quality.

Life history correlates and reproductive biology of Laelius pedatus (Hymenoptera: Bethylidae) in The Netherlands

“…Our studies failed to find a relationship between host size and offspring sex in single-egg clutches, a trend found previously in L. pedatus (Mayhew & Godfray, 1997) and in many other parasitoid spp. (see King, 1987).…”

“…However, all male broods, all female broods, and single egg broods were also produced, suggestive of non-local mating. To resolve this paradox, information on mating stucture is required (Mayhew & Godfray, 1997). We have shown here that females sometimes become sperm depleted late in life, laying all-male broods.…”

“…Mertins (1982) also reports that four Trogoderma species are attacked with rare partial success and that little or no interest is shown in Attagenus megatona F. or Thylodrias contractus Motschulsky (he also reports that the species is unable to attack A. flavipes, c.f. Morgan & Cook, 1994;Mayhew & Godfray, 1997). Mor tality on the three Anthrenus spp.…”

“…The male is usually the last egg to be oviposited (Mertins, 1980;Mayhew, 1996). In solitary clutches, males are laid on very small hosts and females on larger hosts, a strategy known as conditional sex expression, which suggests that females benefit more from large size than males (Mayhew & Godfray, 1997). Female wasps encountering a clutch of eggs laid by a conspecific female will invariably remove them prior to laying her own clutch, a tactic known as ovicide, considered adaptive because egg removal takes little time but reduces competition for resources among her offspring (Mayhew, 1997).…”

Life history studies of Prorops nasuta, a parasitoid of the coffee berry borer

“…The wasp apparently has the ability to regulate the sex of its progeny, but it is not yet understood how this species determines the proportion of the sexes. According to Mayhew and Godfray (1997) and Hardy and Mayhew (1998) the sex allocation of Bethylids is related to the clutch size (higher proportion of males in smaller clutches, reducing mate competition in larger clutches while ensuring male occurrence within smaller clutches) and host quality (larger hosts have a lower proportion of males; they may also, of course, support larger clutches of eggs). In H. hampei the sex ratio (male proportion) is 0.09, and female larvae are almost double the length of male larvae (Bergamin, 1943).…”