Deciphering the associated risk on soil microbes upon use of biopesticides in rice ecosystem.

Plant species, viz Cleistanthus collinus, Lantana camara, and Strychnos nux-vomica are being traditionally used for pest management in rice. However, limited investigation has been carried out to understand the toxic effect of these materials on soil microbes. Hot water extracts of these plants were evaluated for their effects on soil microbial population and enzyme activities along with neem oil and chlorpyrifos as check. Soil microbial population, viz bacteria, fungi, phosphate-solubilizing bacteria (PSB), and asymbiotic nitrogen fixers were unchanged after application of plant extracts. Maximum population of bacteria including PSB and asymbiotic nitrogen fixers were observed in control, whereas, S. nux-vomica, and C. collinus-treated soil had higher number of actinomycetes and fungal population, respectively. Soil microbial biomass did not vary differently among the plant extracts. Application of plant extracts did not alter dehydrogenase, ß-glycosidase, acid phosphatase, alkaline phosphatase, and urease content in soil. Secondary metabolites present in these plant extracts may be responsible for variable effects on soil microbes. Chlorpyrifos had a fleeting negative effect on soil microbes and enzymes in comparison to plant extracts. All the three plants did not have any negative effect on soil microbes and enzymes and can be safely recommended in rice pest management.

Toxicological effect of underutilized plant, Cleistanthus collinus leaf extracts against two major stored grain pests, the rice weevil, Sitophilus oryzae and red flour beetle, Tribolium castaneum.

Toxicity and repellency activity of Cleistanthus collinus (Roxb.) (CC) leaf extracts were evaluated against rice weevil, Sitophilus oryzae (L.) and red flour beetle, Tribolium castaneum (Herbst) under laboratory condition. Five concentration(s) (1%, 1.5%, 2%, 2.5% and 4%) with two controls (acetone and water) treatments along with deltamethrin were used for direct and contact residual toxicity. The insect that survived after CC exposure were transferred to an untreated feeding substrate and the population buildup of subsequent two generation were recorded after 30 (F1) and 60 days (F2). In the contact residual toxicity, highest CC concentration (4%) produced 75% mortality in S. oryzae and 62.5% mortality in T. castaneum during 7 days of exposure, whereas in direct toxicity the mortality were 81% and 58% respectively, for S. oryzae and T. castaneum. The long term effect of CC was apparent in both the insect species, where F2 populations were significantly decreased in the CC treatments. CC treatment at 4% produced similar adult mortality in comparison to deltamethrin at 1%. In addition, repellent activity of CC extracts was observed against both S. oryzae and T. castaneum. This is the first step towards assessing the scientific basis for the understanding the effectiveness of CC extracts against stored grain pests and it could be a viable eco-friendly option for stored grain insect pest management.