Study of the biology of <i>Trichogramma chilonis</i> Ishii (Hymenoptera: Trichogrammatidae) in Mauritius

Abstract

Maruca vitrata F. is a serious pest of bean (Phaseolus vulgaris L.) in Mauritius. During the search of its natural enemies, Trichogramma chilonis Ishii was found to parasitize eggs of M. vitrata for the first time. Laboratory and field studies were conducted to study the biology of T. chilonis developed from M. vitrata eggs.

Trichogramma chilonis females lived for about 8.5 ± 0.7 days in laboratory
and produced an average of 42.4 ± 1.3 eggs during their life time. They laid
80% of their egg complement within four days after emergence. However,
egg production was highest on the first day. The sex ratio of emerging
progeny was 1:2.2 (:).One-day old M. vitrata eggs were preferred for
oviposition whereas 2 and 3-day old eggs for feeding. No parasitism was
observed in 3-day old eggs. The combined effect of egg parasitism and
feeding resulted in more than 77% mortality in one and two-day old eggs.
Only one T. chilonis adult emerged from a parasitized egg.
The choice test showed that T. chilonis females had a preference for
parasitizing eggs of Helicoverpa armigera Hb. to M. vitrata but did not
oviposit in eggs of Plutella xylostella L. In the no-choice test, parasitism in
eggs of H. armigera and M. vitrata was significantly higher than that in
eggs of P. xylostella. Exposed eggs of M. vitrata and H. armigera in the
field were parasitized by T. chilonis while those of P. xylostella were not.

Keywords: Trichogramma chilonis, Maruca vitrata, biology, Plutella
xylostella, Helicoverpa armigera, egg parasitism