N. Gauthier et Jp. Monge, Behavioural and physiological responses to conflicting oviposition stimuliin a synovigenic parasitoid, PHYSL ENTOM, 24(4), 1999, pp. 303-310
The behavioural and physiological responses of the synovigenic parasitoid,
Dinarmus basalis (Rond.) (Hymenoptera: Pteromalidae), were investigated whi
lst the wasps were submitted to conflicting oviposition stimuli: an environ
ment which induced them to restrict egg-laying and a physiological factor,
egg-load pressure, which induced them to lay eggs. When individual females
depleted patches containing hosts parasitized 24 h or 72 h beforehand, they
laid preferentially on unparasitized hosts and the number of eggs laid dec
reased significantly. Although they remained for several days in such patch
es, egg-load pressure did not lead them to modify their strategy (i.e. to a
ccept all the available hosts including the already parasitized ones). In t
his synovigenic species, the oviposition constraint resulted in the retenti
on of oocytes. Dissection and histological observation showed that the unla
id eggs are resorbed, a reproductive regulatory process which has seldom pr
eviously been reported in the presence of unparasitized hosts. This physiol
ogical response was induced by the mere presence of the parasitized hosts r
ather than their density. The females' response was also influenced by the
presence of conspecifics. They still avoided laying on parasitized hosts bu
t the number of eggs laid daily became comparable to that observed in patch
es containing only unparasitized hosts. Thus, D. basalis females adapted th
eir strategy in response to their environment, in which the most significan
t factor seemed to be the quality of the hosts provided, and their physiolo
gy. The originality and the importance of these results are discussed.