Assessment of non-target effects of Bt proteins (Dipel 8L, Vip3Aa70, and Vip3Aa71) on the developmental biology of Bracon hebetor Say parasitizing Chilo partellus (Swinhoe)

Abstract

Bacillus thuringiensis (Bt) based bioinsecticides
and Bt proteins are widely used for the management of
lepidopteran pests. However, their potential effects on
non-target beneficial insects such as parasitoids require
careful evaluation. The present study assessed the impact
of Bt formulations and Vip proteins on the parasitoid
Bracon hebetor through its host, the maize stem borer,
Chilo partellus. Second instar larvae of the maize stem
borer were exposed to LC50
 concentrations of Dipel 8L
and Vip proteins (Vip3Aa70 and Vip3Aa71) for 48 hours.
The LC50
 values were 1.45 ppm for Dipel 8L, 4.17 ppm
for Vip3Aa70 and 4.83 ppm for Vip3Aa71. After feeding
on Bt proteins at LC50
, third-instar C. partellus larvae
were exposed to Bracon hebetor and the developmental
parameters of the parasitoid were recorded. Cocoon period
(days), cocoon weight (mg) and cocoon size (mm) of
the parasitoid showed non-significant differences among
treatments, indicating only mild effects on the biological
traits. Cocoon formation (%) and adult emergence (%)
differed significantly; Dipel 8L resulted in the lowest adult
emergence, while cocoon formation was minimum in the
Vip protein (Vip3Aa70 and Vip3Aa71) treatments, though
differences among Vip proteins were non-significant. The
exposure at LC50
 concentrations of Dipel 8L and Vip3A
proteins caused slight reductions (5.95-7.59 % in cocoon formation and 6.86-10.33% in adult emergence) and thus
exerted no major adverse effects on the developmental
biology of B. hebetor