Effects of Phosalone, Pyridalil and Fenpyroximate on Bracon hebetor life history parameters

Abstract

Introduction: Bracon hebetor Say (Hymenoptera: Braconidae), is one of the important
ectoparasitoid on larval stage of many lepidopterous pests especially Noctuidae and Pyralidae.
These wasps are used widely in biological control programs. Every year a variety of pesticides
are used in cotton fields, which affects natural enemies such as B. hebetor. In this research,
lethal and sub-lethal effects of commonly used pesticides in cotton fields such as Phosalone,
Pyridalil and Fenpyroximate, on B. hebetor were evaluated under laboratory conditions
(25±1ºC, 60±5 r.h. and a photoperiod of 16L: 8D h).
Materials & Methods: In this research, lethal and sub-lethal effects of commonly used
pesticides in cotton fields such as Phosalone, Pyridalil, and Fenpyroximate, on B. hebetor were
evaluated under laboratory conditions (25±1ºC, 60±5 RH. and a photoperiod of 16L: 8D h.).
In the next stage of study, bioassay experiments by application of dipping were carried out on
immature B. hebetor.
Result: The effects of field recommended concentrations of the pesticides were assessed on
the larval and pupal stages of B. hebetor according to IOBC standard methods‚ thus the results
showed that every of three pesticides were classified as slightly harmful. Assessment of
pesticides sub lethal effects on adult warps which were exposed to LC25 revealed, stable
population parameters, biological and reproductive parameters were influenced by this
pesticide. The mean value of Net reproductive rate (R0) and intrinsic rate of increase (rm) for
phosalone, pyridalil and fenpyroximate, were calculated 33.78±0.71, 26.35±0.45 and
40.76±2.43 female/female/generation and 0.21, 0.18 and 0.23 female/female/day, respectively.
Comparison of means using Tukey's test (p<0.05) shows that, different between the means is
significant.
Conclusion: Negative effects of pesticides on parasitoids unknow well but our results showed
that the order of toxicities of the insecticides on B. hebetor was as follows:
phosalone > pyridalil > fenpyroximate and fenpyroximate is suitable pesticide for interment
pest managements.