J. Perez-mendoza et al., Effects of protect-it on efficacy of Anisopteromalus calandrae (Hymenoptera : Pteromalidae) parasitizing rice weevils (Coleoptera : Curculionidae) inwheat, ENV ENTOMOL, 28(3), 1999, pp. 529-534
The parasitoid Anisopteromalus calandrae (Howard) was: very sensitive to di
rect contact with Protect-It, an inert dust formulation containing 90% diat
omaceous earth and 10% silica aerogel. LT(50)s at room temperature and humi
dity were 49 min (95% CL = 48-51) and 72 min (95% CL = 69-74) for males and
females, respectively, in petri dishes containing 7.5 mg dust per square c
entimeter. Under the same conditions, adults of the rice weevil, Sitophilus
oryzae (L.) (Coleoptera: Curculionidae), a host of A. calandrae, were much
less sensitive. Mortality of S. oryzae after a 24-h contact period was 50%
for females and 62% for males. When tested in no-choice laboratory bioassa
ys at 27 degrees C, label rates of Protect-It (200 and 400 ppm) dusted onto
hard red winter wheat, Triticum aestivum, L. (13.9% moisture content) that
was infested with immature rice weevils reduced the longevity of parent A.
calandrae females and significantly reduced parasitization of the weevils
at 3 tested humidities, 43, 60, and 75% RH. Parasitoid progeny production w
as also significantly reduced. At 75% RH, 92.8 +/- 2.9 parasitoid progeny w
ere produced in untreated wheat compared with 12.6 +/- 2.6 progeny in the t
reated wheat. Sex ratio of parasitoid progeny was not significantly affecte
d by the dust treatments at any relative humidity. In two-choice tests in d
ivided petri dish arenas, single A. calandrae females showed a strong avoid
ance of Protect-It-treated wheat and a significant preference for parasitiz
ing weevils in untreated wheat. How ever, significantly more parasitoid pro
geny were produced in dishes in which one-half contained Protect-It-treated
wheat and the other half contained untreated wheat compared with dishes in
which both halves of the divided dishes held untreated wheat. Reasons for
the Protect-It-stimulated oviposition response by A. calandrae are not know
n, but may be related to stress induced by the dust. In separate tests, the
re was no significant difference in emergence of weevils from treated or un
treated a heat, regardless of the weevil age at time of dusting, or the rel
ative humidity at which the dusted wheat was maintained. Our studies provid
e evidence that any natural control of pest insects exerted by local popula
tions of parasitoids, or enhanced biological control by augmentative releas
es of parasitoids, would be adversely affected. by the use of Protect-It or
other diatomaceous earth products on stored grain.