Ecological management of coconut root grub, Leucopholis coneophora Burm

Abstract

The study entitled ‘Ecological management of coconut root grub, Leucopholis coneophora Burm.’ was conducted at the Department of Agricultural Entomology, College of Agriculture, Vellayani, and College of Agriculture, Padannakkad during 2017 to 2019. The main objectives were to study the efficacy of botanical insecticides and biocontrol agents against coconut root grub, L. coneophora. The entire study consisted of two parts, laboratory evaluation and pot culture experiment. The laboratory experiment was conducted for screening various entomopathogenic fungi (EPF), entomopathogenic nematodes (EPN), botanicals and chemical insecticides against coconut root grub. Metarhizium anisopliae (Ma 4) and Beauveria bassiana (Bb 5) at different concentrations (1 x 108, 1 x 109 and 1 x 1010 spores mL-1) were tested. Entomopathogenic nematodes Steinernema carpocasae and Heterorhabditis bacteriophora at 100, 500 and 1000 IJ mL-1 were used for screening. The botanicals such as Azadirachta indica, Gliricidia maculata, Clerodendron infortunatum and Chromolaena odorata @ 25 g kg-1 of soil were screened for their efficacy against root grub. The chemicals used for the experiment comprised of chlorantraniliprole 0.4% G @ 75g a.i ha-1, fipronil 0.3% G @ 75g a.i ha-1 and spinosad 45% SC @ 73g a.i ha-1. Chlorpyriphos 25 % EC @ 225 g a.i ha-1 was used as a chemical check along with untreated control. Fifteen kilograms of sterilized moist soil was taken in a plastic basin and fresh potato tubers were given as feed for root grub. Three grubs were released into the basin and treatments were given one week after the release of grubs. The screening experiment using EPF consisted of eight treatments with three replications. The application of M. anisopliae @ 1 x 1010 spores mL-1 was found to be the most effective (100 % mortality) EPF against root grub and was on par with chemical check at 14 days after treatment (DAT). At 21 DAT, B. bassiana @ 1 x 1010 spores mL-1 resulted 100 per cent mortality and was on par with M. anisopliae @ 1 x 1010 spores mL-1 and the chemical check. At 28 DAT, M. anisopliae @ 1 x 1010 spores mL-1 and B. bassiana @ 1 x 1010 spores mL-1 brought about 100 per cent mortality of grubs, which were on par with the chemical check chlorpyriphos 20 % EC @ 225g a.i ha-1 (100 %), followed by M. anisopliae @ 1 x 109 spores mL-1 (92.58 %) and B. bassiana @ 1 x 109 spores mL-1 (85.17 %). The screening experiment with EPN consisted of eight treatments with three replications and the results revealed that all the treatments except chemical check failed to cause infection on grubs upto 10 DAT. Among the botanicals, A. indica application showed 48.14 per cent mortality of root grubs followed by C. infortunatum (37.03 %) at 30 DAT. The effect of chemical insecticides on root grub was conducted with five treatments and four replications. Fipronil 0.3% G @ 75g a.i ha-1 exhibited 97.22 per cent mortality and was on par with the chemical check at nine DAT followed by chlorantraniliprole 0.4% G @ 75g a.i ha-1 (74.99 %). Promising treatments viz. M. anisopliae (1 x 1010 spores mL-1, 1 x 109 spores mL-1), B. bassiana (1 x 1010 spores mL-1, 1 x 109 spores mL-1), chlorantraniliprole 0.4% G @ 75g a.i ha-1, and Fipronil 0.3% G @ 75g a.i ha-1 from laboratory experiments were selected and evaluated in a pot culture experiment and were laid out in CRD with eight treatments and three replications. Chlorpyriphos 25 % EC @ 225 g a.i ha-1 was used as a chemical check along with untreated control. Fodder grass variety CO-3 was raised in pots and first instar grubs were released after the establishment of the crop. The results of the pot culture experiment indicated that the application of fipronil 0.3% G @ 75g a.i ha-1 resulted in 100 per cent mortality and was on par with the chemical check at 28 DAT followed by M. anisopliae @ 1 x 1010 spores mL-1 (85.17 %). The treatments B. bassiana @ 1 x 1010 spores mL-1 (77.77 %), chlorantraniliprole 0.4 % G @ 75g a.i ha-1 (74.06 %) and M. anisopliae @ 1 x 109 spores mL-1 (74.06 %) were found to be on par at 28 DAT. From the present study, it can be concluded that the application of entomopathogenic fungi M. anisopliae @ 1 x 1010 spores mL-1 is a promising option for the management of first instar grubs of L. coneophora followed by B. bassiana @ 1 x 1010 spores mL-1. Soil application of neem leaves @ 25 g kg-1 of soil can enhance the suppression of root grubs. The results clearly indicate the possibility of reducing the use of chemical insecticides by resorting to botanicals and biocontrol agents.

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