Crossing incompatibility between Trichogramma minutum and T-platneri (Hymenoptera : Trichogrammatidae): Implications for application in biological control
R. Stouthamer et al., Crossing incompatibility between Trichogramma minutum and T-platneri (Hymenoptera : Trichogrammatidae): Implications for application in biological control, ENV ENTOMOL, 29(4), 2000, pp. 832-837
The two egg parasitoid species Trichogramma minutum Riley and T. platneri N
agarkatti are closely related. No morphological or molecular characters are
known to distinguish them. Their treatment as distinct species rests on th
e absence of female offspring in between-species crosses. The current speci
es definitions, which must be considered tentative, assume their natural ra
nges to differ, with T. minutum occurring east of the Rocky Mountains and T
. platneri occurring to the west. Both species are used throughout North Am
erica for the biological control of moths in orchards and forests. They are
available to growers and researchers through a large number of biological
control suppliers. Because the species can only he identified after crosses
with known cultures, it is likely that producers often cannot be sure of t
he identity of their wasps. Here we studied the causes of the lack of femal
e offspring in the between-species crosses and what happened when one speci
es is released for biological control in the native area of the other. Our
results show that females in between-species crosses are inseminated and us
e the sperm to fertilize their eggs, but that these fertilized eggs die. In
addition, females do not preferentially mate with males of their own speci
es when exposed to conspecific and nonconspecific males. These results are
used in a model to predict the effect of releasing the non-native species i
n the native area of the other species. This model shows that such introduc
tions can result ina prolonged and substantial reduction of intended biolog
ical control.