Reproductive behaviour of Aphidius ervi Haliday (Hymenoptera: Aphidiidae : a thesis presented in partial fulfi[l]ment of the requirements for the degree of Doctor of Philosophy in Plant Science (Entomology) at Massey University, Palmerston North, New Zealand
Aphidius ervi Haliday is a cosmopolitan parasitoid species of several major aphid
pests on economically important crops. Prior to this research, little information was
available on its reproductive behaviour. Emergence of A. ervi peaks during the first
few hours of the photophase with males being protandrous. Females become sexually
mature earlier than males and oviposit primarily in the photophase. Aphids parasitised
in their early instars die before reproduction but those parasitised in later instars
produce a limited number of progeny. Females prefer aphids of 3- to 5-d-old over the
younger and older aphids for oviposition. Females ovipositing in 4- to 7-d-old aphids
have more fitness gains in terms of progeny body size and egg load at emergence.
Fertilised eggs are more likely deposited in large hosts and unfertilised eggs in small
ones. Large individuals have greater longevity, large males father more progeny, and
large females have higher fecundity, parasitism and greater ability in host searching.
However, with increasing body size females gain more than males in longevity and
fecundity but males gain more than females in the number of female progeny. Males
can inseminate up to nine females and they carry about 82% effective sperm at
emergence and replenish about 18% sperm during their adult life. Females adjust the
oviposition and sex allocation strategies in response to increasing host density with
higher number of aphids parasitised at higher host densities and lower proportion of
female progeny produced at lower host densities. Males play an active role in mating
behaviour. Males having mating experience, and being large or younger, respond to
females more quickly and perform better courtships resulting in higher mating success.
Males prefer larger and younger females for mating probably because the latter have
greater reproductive potential. Males optimize the use of their sperm based on the
availability of their sperm and the reproductive status (age) of females. The switchingoff
of female receptivity of male mating attempt after the mating is a gradual process.
Some females accept the second males within 1 minute since the termination of the
first mating. The shorter mating period in the second mating suggests that females
remate probably due to the gradual process of switching-off of female receptivity
rather than the insufficient sperm transformation during the first mating. Males
prolong their mating duration in male-biased operational sex ratio to reduce the
probability of female remating.