MSc

A study titled “Bioefficacy of entomopathogenic fungi against rice bug, Leptocorisa oratorius Fab. (Alydidae: Hemiptera)” was carried out at Dept. of Agricultural Entomology to evaluate efficacy of three entomopathogenic fungi namely Beauveria bassiana, Metarhizium anisopliae and Lecanicillium lecanii for the biocontrol of rice bug. The preliminary evaluation comprised of pot culture experiment with the fungi being applied at four different concentrations ranging from 105 to 108 spores ml-1 along with insecticide malathion 500g a.i. ha-1 and an untreated control. Mortality of rice bugs were recorded at 24h interval for 10 days.
Ten days after treatment B. bassiana was the most effective among the three fungal pathogens tried, with mortality values ranging from 68.88 per cent at 105 spores per ml to the highest value of 97.77 per cent at 108 spores per ml. This was followed by malathion with 95.55 per cent and B. bassiana at 107 spores per ml with 93.33 per cent mortality respectively, all being on par with each other. M. aniospliae and L. lecanii at the rate of 108 spores per ml registered the highest mean mortality of 71.11 and 62.22 per cent respectively.
The most effective concentrations of each of the entomopathogenic fungus identified in the pot culture experiment was evaluated along with malathion 500g ai ha-1 under field conditions during August-December at Vellanikkara and again during January-May in a Farmer field at Muthuvara. Observations on rice bug population as well as the damage caused by rice bug were recorded before treatment as well as at five and ten days after the treatment.
The results of field evaluation broadly agreed with the findings of the pot culture studies. Malathion registered the lowest mean bug population in both the experiments. Ten days after treatment B. bassiana recorded a significant reduction in mean rice bug population which was found superior to both M. anisopliae and L. lecanii and was on par with malathion.
As in case of bug population malathion continued to record the lowest grain damage among all the treatments. In the first field experiment, malathion recorded an average grain damage of 8.67 per cent at ten days treatment and was followed by B. bassiana with 13.08 per cent grain damage, both being at par. M. anisopliae and L. lecanii recorded mean grain damage of 24.01 and 22.05 per cent respectively and were on par with control (27.09 per cent grain damage). A similar trend was observed fifteen days after treatment as well.
Field evaluation at Muthuvara confirmed the finding of the first field evaluation. Malathion recorded the lowest grain damage of 13.46, 15.18 and 14.64 per cent 5, 10 and 15 days after first round of treatment and was significantly superior to other treatments. Plots treated with B.bassiana were next in terms of grain damage with 16.67, 15.8 and 18.22 per cent damage at 5, 10 and 15 days after treatment respectively. It was significantly superior to both M. anisopliae and L. lecanii, both of which were on par with control
The pot culture as well as field evaluation have demonstrated the efficacy of the local isolate of Beauveria bassiana to reduce the infestation by gundhi bug L. oratorius in rice. It constantly proved to be as effective as the insecticide malathion. It had caused greater reduction in bug population and had led to lower grain damage in all three experiments than the insecticide, though the differences were not significant. From the above, it can be concluded that the local isolate of B. bassiana could be a highly potent biocontrol agent against rice bug.
However, given the time lag between the application of treatment and any appreciable reduction in bug population, timing of the treatment could be critical in minimizing grain damage by the bug. Application of the fungus at milky grain stage could be insufficient to check the damage to the grains. Advancing the timing of treatment by about ten days to panicle initiation stage might prove to be a better strategy, against a pest that causes heavy damage in a relatively short period.