Sub-lethal doses of Nucleopolyhedrosis Virus and synthetic ınsecticides alter the biological parameters of Helicoverpa armigera Hübner (Lepidoptera: Noctuidae)

Resistance management is very important for devising control strategies of polyphagous insect-pests like Helicoverpa armigera Hübner (Lepidoptera: Noctuidae). Considering the importance of resistance management, demographic features of selected and unselected populations of H. armigera were studied in 6 different treatments viz. emamectin benzoate, Helicoverpa armigera Nucleopolyhedrosis Virus (HaNPV), emamectin benzoate+HaNPV, spinetoram, spinetoram+HaNPV and control. Higher values for fecundity, intrinsic rate, the finite rate of increase (λ) were recorded in the control of selected as compared to the rest of treatment. Similarly, higher values for these population parameters viz. oviposition days, fecundity, intrinsic rate, the finite rate of increase were calculated in the unselected control. Similarly, net reproductive rate (R0) for selected and unselected control was higher as compared to the rest of the treatments. It may happen because these kinds of selection pressures can result in decreased fitness of the test insect thus decreased fitness of H. armigera in different treatments was observed as compared to the control. Additionally, quicker development of susceptible insects was observed because susceptible insects were growing without any stressor (xenobiotics) as compared to the rest which contributed to their faster development.

Effect of a low cost diet on the cotton leaf worm, Spodoptera littoralis nucleopolyhedrosis virus pathogenicity and sterile insect technique

Background Mass rearing cost of Spodoptera littoralis (Boisd.) (Lepidoptera: Noctuidae) is one of the critical methods for the successful utilization of Baculovirus pathogenicity and sterile insect technique (SIT). Effectiveness of both SIT and S. littoralis Nucleopolyhedrosis Virus (SpliNPV) was assessed in response to plant-based diet and substitution of agar with commercial sources of gelling components as feed. Results Pupal and adult recoveries produced by castor bean leaves were significantly high, followed by the agar-based diet. Moreover, larval durations were significantly prolonged for (starch + gelatin)-based diet than the other dietary diets. Obviously, SpliNPV pathogenicity against the larvae reared on (starch + gelatin)-based diet was 2.5 and 2 times higher than those reared on castor leaves and agar-based diet, respectively. Contrary to expectation, the sterility doses of male moths produced by castor leaves and agar-based diet were relatively similar. Conclusion The findings suggest that the lowest cost diets (starch + gelatin)-based diet could be used effectively for increasing the SpliNPV pathogenicity, while either castor leaves or agar-based diet could be considered as a promising choice for SIT program.

Impact of emamectin benzoate on nucleopolyhedrosis virus infectivity of Spodoptera littoralis (Boisd.) (Lepidoptera: Noctuidae)

Background Attempts based on increasing the efficacy of Baculovirus and/or reducing the application concentration of synthetic insecticides through integrated lepidopteran management are appreciated role for conserving the environment. Impact of the multiple nucleopolyhedrosis virus (SpliMNPV) with emamectin benzoate (Em) against the cotton leaf worm, Spodoptera littoralis, was examined to identify the effective strategy for applying both agents in the control program successfully. Main body The LC50 and LC90 were drastically decreased from 1.9 × 106 and 1.0 × 1010 PIB/ml in SpliMNPV treatment to reach 8.87 × 101 and 1 × 104 PIB/ml, respectively in the SpliMNPV concentrations + Em LC25 treatment. This interaction was considered as potentiation. Larvicidal activity of Em was highly increased by Em concentrations + SpliMNPV LC25 treatment than the separately Em treatment; however, this interaction was considered as additive. Moreover, the mixture treatment (SpliMNPV LC99 + Em LC50) provided almost full protection of viral pathogenicity up to 48 h at natural exposure periods. Furthermore, the mixture treatment had a negative impact on the insect survival and reproduction of treated individuals. Conclusion Results indicated that the virus infectivity was increased by a mixture treatment of SpliMNPV + Em in particular facing UV sunlight, which causes virus degradation as well as reduced the effective doses of Em. These findings suggest that this simultaneous treatment maybe an effective technique to be applied in S. littoralis control strategy.