Reproductive strategy as a major factor determining female body size and fertility of a gregarious parasitoid

Abstract

The generally known “adult size‐fitness hypothesis” (ASFH) is applied to the gregarious parasitic wasp Anaphes flavipes (Foerster, 1841) (Hymenoptera: Mymaridae). ASFH is dependent on the reproductive strategy of the mother, which means the larger females have more offspring compared to smaller females. Two main factors, the mother's body size and food quantity received during larval development, can affect the body size of the offspring. For the first time, we present a study on the relative effect of both factors on fitness of the same species, wasp A. flavipes. Our data confirmed that females of A. flavipes with larger body sizes had more offspring compared to smaller ones. At the same time, mother's body size does not seem to affect the body size of the offspring. The other studied factor, quantity of food received during larval development, can be influenced by reproductive strategy (number of parasitoids developing in one host egg), host quality or the duration of development. We found only the reproductive strategy to have a statistically significant effect on body size. We demonstrated that the variable reproductive strategy (VRS) of wasp A. flavipes causes a plasticity in body size and future number of offspring. The generally known “trade‐off” scheme (more small offspring or fewer bigger offspring) does not apply to A. flavipes, because their large females have more offspring and it is their reproductive strategy that determines body size.

Host population density and presence of predators as key factors influencing the number of gregarious parasitoid Anaphes flavipes offspring

“…One ( a ), two ( b ) and three ( c ) wasps developing per host egg.

Figure 3The number of wasps developing in one host egg, their adult body size and future fertility are influenced by the host population density of the host. Each female has 34 offspring, but the size of their offspring depends on the number of individuals developed in one host 28 . Wasps lay a higher number of eggs into one host egg and therefore produce smaller offspring if the population density of hosts is “low” compared “medium” and “high” population densities of hosts.

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“…The host spectrum of the wasp includes species of the genera Lema and Oulema (Coleoptera: Chrysomelidae), including an economically important crop pest - the cereal leaf beetle O. melanopus 25,27 . Recently, we observed that in comparison to smaller females, larger females have more offspring and that the adult size of the offspring is directly determined by the number of offspring developing in one host egg 28 .…”

“…However, in some cases, larger hosts do not indicate higher nutritional value 29,30 , and parasitoids from smaller but more nutritionally valuable hosts have a larger body size 31 . Eggs of the Oulema species are the same size 28 . Therefore, we expect that species of Oulema do not differ in nutritional value and do not affect either host preference or the number of offspring.…”

“…Host density influences the number of parasitoids developed in one host 20,21 . We assume that with a plethora of host eggs available, the female A. flavipes also increases her fitness if she lays a smaller number of offspring into one host, as this would ensure a larger body size of the offspring 28 . (4) Presence of predators .…”

Host Specificity of the Parasitic Wasp Anaphes flavipes (Hymenoptera: Mymaridae) and a New Defence in Its Hosts (Coleoptera: Chrysomelidae: Oulema spp.)

“…(O. duftschmidi Redtenbacher, 1874, O. gallaeciana Heyden, 1879, and O. melanopus Linnaeus, 1758) [22,23]. Larvae and adults of Oulema species damage the leaves of cereals (barley, wheat and oats), and they are an economically important crop pest in Europe and North America [24][25][26]. For example, in agricultural areas around the world, insect pests reduce grain crop yields by 5% to 20 % every year [27].…”