Background
Entomopathogenic nematodes (EPNs) are one of the widely studied biological control agents. The present study was conducted to evaluate the efficacy of two EPNs species, Heterorhabditis bacteriophora (Poinar) (Rhabditida: Heterorhabditidae) and Steinernema aciari (Qui, Yan, Zhou, Nguyen and Pang) (Rhabditida: Steinernematidae), isolated locally from soils of Majuli river island, Assam, India against two important subterrenean pests; Odontotermes obesus (Rambur) (Isoptera: Termitidae) and Agrotis ipsilon (Hufnagel) (Lepidoptera: Noctuidae) under laboratory conditions.
Results
In case of O. obesus, mortality percent was recorded by H. bacteriophora after 72 h. at 300 IJs/termite and by S. aciari at 250 and 300 IJs/termite after 96 h. The lowest LD50 and LT50 values obtained for H. bacteriophora were 13.054 IJs/termite and 26.639 h., respectively, while those of S. aciari were 42.040 IJs/termite and 31.761 h., respectively. With respect to A. ipsilon, H. bacteriophora registered a highest mortality rate at 300 IJs/larvae after 144 h. S. aciari showed 100 percent mortality at 300 IJs/larva after 168 h. The lowest values of LD50 and LT50 for H. bacteriophora were 35.711 IJs/larva and 83.050 h., respectively. The lowest values of LD50 and LT50 for S. aciari were 71.192 IJs/larvae and 97.921 h., respectively. Overall, H. bacteriophora displayed more virulence toward O. obesus and A. ipsilon than S. aciari.
Conclusion
Both native EPNs were found effective against O. obesus and A. ipsilon. However, H. bacteriophora was more virulent toward O. obesus and A. ipsilon than S. aciari under the laboratory conditions.
Experiments were carried out in the farmer’s field at Jorhat during 2015-16 and 2016-17 to study the population dynamics of red ant Dorylus orientalis Westwood in potato crop. The incidence of D. orientalis was observed both under flood free/ and prone conditions in three villages each, during potato growing season. These data were correlated with weather factors. The effect on population buildup was studied with observations at fortnightly interval starting from 1st fortnight of October to 2nd fortnight of February through fixed plot surveys. The observations revealed that maximum incidence (36.5, 33.2 and 30.1; 35.2, 32.5 and 29.8/ pit) was observed in Charaibahi, Karangia and Hokai Khangia villages, respectively during the 1st fortnight of January. In contrast, in the flood prone villages, incidence was observed to be negligible. Correlation coefficients of incidence with weather factors revealed that minimum temperature, soil temperature (morning and evening) and evaporation rate show a significantly negative correlation; whereas relative humidity (RH) (morning and evening) exhibited significant positive correlation in flood free villages. In flood prone villages minimum temperature as well as morning soil temperature showed significant negative correlation (2015-16); in contrast, in flood prone villages, RH (morning and evening) showed significant positive correlation (2016-17).
A b s t r a c t A r t i c l e I n f oInsecticide resistance and the demand for reduced chemical inputs in agriculture have provided a movement to the development of alternative measures of controlling insect pests. Myco-biocontrol offers an attractive alternative to the use of chemical pesticides.Entomopathogenic fungi are potential biological control agents mainly by reason of their wide host range, high reproductive capabilities, target specific activity, short generation time, and resting stage or saprobic phase producing capabilities that can ensure their survival for a longer time when no host is present. However, a primary requirement for the commercial use of entomopathogenic fungus as myco-biocontrol agents is the susceptibility of the insect and also the virulence of the fungus. They are naturally occurring organisms which are perceived as less damaging to the environment. The current paper could enlightened regarding the recent progress in the field of entomopathogenic fungi and their possible mode of action along with further improvement aspects for perceptive of myco-biological control of insect pests.
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