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.
Basic biological attributes and feeding potential of three major predators viz., the seven spotted lady bird beetle Coccinella septempunctata Linnaeus and two syrphids Episyrphus viridaureus (Wiedemann) and Betasyrphus isaaci (Bhatia), of mustard aphid, Lipaphis erysimi were studied under laboratory conditions. The predators were multiplied on mustard aphids reared on mustard plants.C. septempunctata, E. viridaureus and B. isaaci completed their life cycle in 68.5± 6.5 days, 47±2 and 41±2, respectively. Coccinella septumpunctata completed the larval growth with four larval instars, while both the syrphids terminated the larval growth with three instars. Final instars of all the three predators were found to have highest predatory potential than the younger instars. C. septumpunctata was found to be the most dominant predator of mustard aphid with average lifetime consumption of 4312±537.74 aphids, followed by E. viridaureus (416.67±6.76 aphids) and B. isaaci (338±7.89 aphids). All the three predators have the potential to reduce the mustard aphids; however, C. septumpunctata has a maximum predatory potential with a longer life, which makes this species as an excellent bioagent of L. erysimi and further research on their utilization on a large scale should be undertaken.
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