Abstract
BackgroundIn the present study, the efficacy of two isolates of Beauveria bassiana namely, BKN20 and BKN1/14 was evaluated against the tea mosquito bug (TMB), Helopeltis theivora, Waterhouse (Hemiptera: Miridae) damaging harvestable shoots of tea plants in the Dooars and Darjeeling regions of West Bengal, India.ResultsLaboratory study revealed that, in both isolates, BKN20 was more pathogenic than BKN1/14, exhibiting 76% mortality of the test insect. The BKN20 isolate was formulated as an aqueous suspension (5%AS), and evaluated against TMB through micro-plot trials in tea plantations. The Micro-plot field study revealed a maximum of 72.19% reduction in the shoot damage due to TMB in plots sprayed with a 1000 ml/ha concentration of BKN20 5%AS containing 2 × 107 conidia/ml, as compared to the synthetic insecticide (Thiamethoxam 25%WG), where a 63.12% reduction in the shoots was recorded. Furthermore, different concentrations of the formulated BKN20 5%AS were evaluated against the test insect at 2 locations of tea gardens in the Dooars and Darjeeling regions. The results from both locations revealed that 1000 and 1200 ml/ha concentrations of BKN20 5%AS (each concentration containing 2 × 107 conidia/ml) significantly (p < 0.05) reduced the TMB population and they were more effective than Thiamethoxam 25%WG (120 g/ha). However, non-significant differences in crop yields were recorded. The formulation BKN20 5%AS was found to be non-pathogenic to non-target insects, i.e. natural enemies present in the tea ecosystem. BKN20 5%AS had no phytotoxic effect on the tea leaves, with acceptable organoleptic attributes.ConclusionThe BKN20 isolate could be commercialized as an alternative microbial insecticide to reduce the load of chemical insecticides in the tea ecosystem.
Highlights
In the present study, the efficacy of two isolates of Beauveria bassiana namely, BKN20 and BKN1/14 was evaluated against the tea mosquito bug (TMB), Helopeltis theivora, Waterhouse (Hemiptera: Miridae) damaging harvestable shoots of tea plants in the Dooars and Darjeeling regions of West Bengal, India
In vitro bio‐efficacy of the B. bassiana against TMB The results of the in vitro bio-efficacy test showed that both isolates BKN20 and BKN1/14 were pathogenic to the TMB and caused significant insect mortality (Fig. 1)
There was non- significant difference in the mortality between the 2 isolates (p > 0.05), the BKN20 isolate was considered for its further formulations and field studies because of its higher pathogenicity on the TMB
Summary
The efficacy of two isolates of Beauveria bassiana namely, BKN20 and BKN1/14 was evaluated against the tea mosquito bug (TMB), Helopeltis theivora, Waterhouse (Hemiptera: Miridae) damaging harvestable shoots of tea plants in the Dooars and Darjeeling regions of West Bengal, India. The TMB remains active throughout the year, and unchecked infestation leads to 100% of the crop loss under favorable conditions if the appropriate management practices are not appropriately applied (Muraleedharan 1992). Continuous and non-judicial use of these chemical insecticides leads to certain undesirable issues such as water pollution, degradation of valuable soil microbes, decline in biological control agents, resurgence, development of resistance in insect pests, and pesticide residues in the manufactured tea (Roy et al 2008). To address these undesirable situations, exploring non-chemical control strategies has become essential. The application of the Microbial Control Agents (MCAs), especially entomopathogens plays a major role in the management of insect pests of tea plants in an ecofriendly way
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