Effects of zeolite formulations on the mortality and progeny production of Sitophilus oryzae and Oryzaephilus surinamensis at different temperature and relative humidity levels

Abstract

The insecticidal potential of two natural zeolite formulations, Zeocem and Mycostop, was tested against the rice weevil Sitophilus oryzae (L.) and the sawtoothed grain beetle Oryzaephilus surinamensis (L.) on wheat, at the dose rates of 0.25, 0.50, 0.75, and 1 g/kg. The bioassays were carried out under laboratory conditions at three temperature levels (20, 25, and 30οC) and two relative humidity (r.h.) levels (55, 75%). Mortality was recorded after 7, 14, and 21 d of exposure and progeny production was recorded 65 d later. Complete (100%) mortality was achieved only for O. surinamensis adults with Zeocem for most temperature and r.h. combinations tested. Progeny production for this species was extremely low. In contrast, mortality for S. oryzae was much lower and did not exceed 87% after 21 days at any of the combinations tested, while progeny production was high. For O. surinamensis exposed to Mycostop, mortality after 21 days did not exceed 97% for all temperature and r.h combinations, while overall progeny production was low. Moreover, S. oryzae mortality was generally low and did not exceed 56%, while progeny production for this species was high for most temperature and r.h. combinations. Despite the fact that some general trends were evident, the effect of temperarature and r.h. in zeolite efficacy was often found inconclusive. The results of the present study illustrated the insecticidal potential of zeolites for the contol of certain stored product insect species, which requires additional investigation.