Abstract:
The insecticidal efficacy of entomopathogenic fungi Beauveria bassiana (Balsamo) Vuillemin, diatomaceous earth SilicoSec and a new chemistry insecticide thiamethoxam was evaluated in various laboratory bioassays as well in on farm trials against one of the major stored grain insect species Rhyzopertha dominica F. (Coleoptera: Bostrychidae). Initially, the temporospatial distribution and seasonal patterns of R. dominica were studied in two types of storage structures i.e. mud bins and steel bins. Followed by laboratory bioassays conducted to investigate the effect of dose rate, grain type, insect population (strain), exposure interval and storage period on the insecticidal effectiveness of all three control measures against the test insect species. The findings of the current studies revealed that the densities of R. dominica were higher in mud bins as compared to steel bins and the numbers of beetles were low immediately after bins were filled in July, peaked in August, declined to almost zero in January and remained at low levels until end of March. In laboratory bioassays, when DE was combined with thiamthoxam, individually the thiamethoxam was more effective compared with DE alone. Significant differences in adult mortality were also recorded among grains and populations tested when DE was used with B. bassiana and the combined use of DE and B. bassiana considerably increased adult mortality as compared with their individual application. The residual effectiveness of all three test substances was decreased over the 9 months of storage period and the maximum mortality was observed in the combination of DE with thiamethoxam but on the other hand, the maximum rate of mycosis and sporulation in the cadavers of R. dominica was observed where B. bassiana was applied alone at the lowest dose rate. During on farm trials, the least number of surviving adults, minimum percent grain damage was observed for DE, insecticide combination but DE with B. bassiana provided the long-term protection as compared with the remaining treatments.
