ABSTRACT
Entomopathogenic nematodes (EPN) belonging to the families of Steinernematidae and Heterorhabditidae are obligate pathogens of a wide range of insects. But their survival and efficacy is adversely affected by the temperature. Therefore, in the present study, we determined the survival ability of Steinernema carpocapsae (Weiser) and Heterorhabditis indica (Poinar) infective juveniles (IJ) by exposing them to various temperatures. Results showed that the percentage survival with the maximum exposure time (48 h) at 25 and 40°C, for S. carpocapsae was 100 and 32.93%, respectively. H. indica which also showed 100% survival after exposure to 25°C, did not survive at 40°C. Among the nematodes, S. carpocapsae showed more tolerance to high temperature compared to H. indica and exposure time also significantly different in both nematodes. When IJs used as inoculum source after exposing to various temperature levels, the percent penetration was reduced and, importantly, progeny production was very less on Greater wax moth larvae. On desiccation, IJs of both S. carpocapsae and H. indica showed significant survivalability. H. indica IJs showed significantly more survival compared to S. carpocapsae when exposed to different desiccating levels.
ABSTRACT
Abstract Diamondback moth (DBM), Plutella xylostella (Linnaeus), is a notorious pest of brassica crops worldwide and is resistant to all groups of insecticides. The insect system harbors diverse groups of microbiota, which in turn helps in enzymatic degradation of xenobiotic-like insecticides. The present study aimed to determine the diversity of gut microflora in DBM, quantify esterase activity and elucidate their possible role in degradation of indoxacarb. We screened 11 geographic populations of DBM in India and analyzed them for bacterial diversity. The culturable gut bacterial flora underwent molecular characterization with 16S rRNA. We obtained 25 bacterial isolates from larvae (n = 13) and adults (n = 12) of DBM. In larval gut isolates, gammaproteobacteria was the most abundant (76%), followed by bacilli (15.4%). Molecular characterization placed adult gut bacterial strains into three major classes based on abundance: gammaproteobacteria (66%), bacilli (16.7%) and flavobacteria (16.7%). Esterase activity from 19 gut bacterial isolates ranged from 0.072 to 2.32 µmol/min/mg protein. Esterase bands were observed in 15 bacterial strains and the banding pattern differed in Bacillus cereus – KC985225 and Pantoea agglomerans – KC985229. The bands were characterized as carboxylesterase with profenofos used as an inhibitor. Minimal media study showed that B. cereus degraded indoxacarb up to 20%, so it could use indoxacarb for metabolism and growth. Furthermore, esterase activity was greater with minimal media than control media: 1.87 versus 0.26 µmol/min/mg protein. Apart from the insect esterases, bacterial carboxylesterase may aid in the degradation of insecticides in DBM.