Synergistic interaction of biocides and insecticides on tomato fruit borer helicoverpa armigera (Hubner)

Abstract

The tomato fruit borer Helicoverpa armigera (Hubner) is a serious pest of several cultivated crops and has attained global importance. H. armigera displays formidable biological profiles based on multihost feeding, strong flying ability and genetic versatility, and consequently it resists any synthetic insecticide used to control it world wide. This pest is out of control precisely because of overuse of synthetic insecticides, which has led to development of resistance and destruction of natural enemy complex. Hence the present study was carried out to investigate the efficacy and interaction of different plant extracts, microbial pesticides and synthetic chemicals, alone and in combination against H. armigera to reduce the cost, to avoid the after effects of commonly used insecticides and to consider its fitness in different management options.

The population of H. armigera was found to be more during October to March period. There was no incidence of pest from July to September period. Among the four ecosystems, tomato recorded the highest number of larvae followed by bhendi, bittergourd and cowpea. The species of natural enemies recorded on H. armigera during the survey period were Carcelia illota, Apanteles taragamae, Chrysoperla carnea, Nosema sp. and Nomuraea rileyi. All these natural enemies are being reported for the first time on H. armigera in Kerala.

The plant aqueous extracts (Acorus calamus Linn. , Andrographis paniculata Wall. and Vitex negundo Linn. ) on their own, are not very highly effective, as they cause only about 30 to 40 per cent mortality at five per cent concentration. All the essential oils (Citronella winterianus Jowitt., Cymbopogon flexuosus Steud., Kaempferia galanga Linn. and Cymbopogon martinii Roxb.) are causing more than

50 per cent mortality except citronella oil (C.winterianus). Palmarosa oil (C. martinii) at five per cent concentration recorded the highest percentage of mortality.

In the compatibility study, all the three-entomopathogenic fungi (Nomuraea rileyi, Metarhizium anisopliae and Beauveria bassiana) were found to be incompatible with essential oils and compatible with plant extracts and insecticides. But all the commercial formulations of Bacillus thuringiensis were compatible with plant extracts, essential oils and insecticides.

The bioassay of entomopathogens with botanicals and insecticides under laboratory conditions produced the following results

In the entomopathogenic fungi and plant extracts combinations, N. rileyi + V. negundo (76.6 per cent) M. anisopliae + V. negundo (63.3 per cent) and B. bassiana + V. negundo (56.6 per cent) recorded the maximum mortality.

The treatments N. rileyi+ spinosad (96.6 per cent), B. bassiana+ spinosad and M. anisopliae + spinosad (93.3 per cent) recorded the highest mortality in entomopathogen + insecticide combinations. A drastic reduction in LT50 value was noticed in combination treatments.

Among the bacterial formulations + plant extract combination, Delfin + V. negundo (83.3 per cent) recorded the highest mortality percentage among the entire three (Halt, Delfin and Dipel) combination products. The time mortality response was reduced from six to seven days to three to four days in combinations.

In the case of bacterial formulations + essential oil, the maximum mortality was recorded in B. thuringiensis (Halt, Delfin and Dipel)+ C. martinii followed by B. thuringiensis + K. galanga.

The treatment combinations Halt + spinosad, Delfin + spinosad and Dipel + spinosad recorded the maximum mortality percentage. The mean lethal time could be decreased drastically in combinations when compared to individual treatments.

The combination NPV + V. negundo recorded the highest mortality percentage in NPV + plant extract combinations. Among the NPV + essential oil combinations, NPV + K. galanga recorded the highest mortality percentage followed by NPV + C. martinii, NPV + C. flexuosus and NPV + C. winterianus. NPV + spinosad combination recorded the highest mortality percentage in NPV + insecticide combinations.

The combined treatment of NPV and B. thuringiensis with plant extracts significantly reduced the digestive enzyme (protease, α - amylase, β - amylase and lipase) activity in the midgut of H. armigera.

The results of the field experiment indicate that the percentage mortality was more in biocide (B. thuringiensis, NPV and N. rileyi) and insecticides combinations when compared to the individual treatments. The study has identified eight such combinations, which are immediately field worthy. This technology is considered as eco- friendly and economically viable in nature. The present findings will be of immense help to the ordinary farmer and take him out of debt traps and offer him a better future.