| Abstract |
The spider mite, Tetranychus truncatus Ehara is a polyphagous mite pest infesting many economically important crops of Kerala. Synthetic acaricides, though effective in mite management, pose several adverse effects to human and environment, demanding a shift to safer and easily biodegradable products. Exploitation of botanicals can be a viable alternative to synthetic acaricides to overcome these hazards. However, botanicals have not been evaluated and effectively utilized for mite pest management in Kerala. The study entitled “Bioefficacy of botanicals against the spider mite, Tetranychus truncatus Ehara (Prostigmata: Tetranychidae)” was carried out at Acarology Laboratory, Department of Agricultural Entomology, College of Horticulture, Vellanikkara during 2018 to 2020. The objectives of the study were to evaluate the efficacy of botanical extracts against T. truncatus, to identify bioactive solvent fractions of promising plant extracts against T. truncatus, and to test the safety of bioactive fractions to the predatory mite, Neoseiulus longispinosus (Evans) and the acaropathogen, Acremonium zeylanicum (Petch). The crude aqueous (5, 7.5 and 10%) and methanol (1 and 2 %) extracts of ten plants viz., Acorus calamus L., Bacopa monnieri (L.) Pennell, Quassia indica Gaern., Eucalyptus sp., Lantana camera L., Aegle marmelos (L.) Correa, Annona squamosa L., Vitex negundo L., Carica papaya L. and Ocimum sanctum L. were evaluated at different concentrations for their efficacy against egg and adult of Tetranychus truncatus Ehara in laboratory bioassays. The aqueous extract of the botanicals, though did not show any ovicidal action, differed significantly in their adulticidal action. The aqueous seed extract of A. squamosa and leaf extract of C. papaya, both at 10 per cent concentration recorded highest mortality (98.67%) of adults, five days after treatment. B. monnieri (10%) and A. squamosa (7.5 and 5%) also recorded mortality on par with these treatments. Appreciable adulticidal activity was also recorded by B. monnieri (7.5 and 5 %), A. calamus (10%), C. papaya (7.5%) and L. camera (10%). The methanol extract of the botanicals were found to be effective against the adults of T. truncatus. Cent per cent mortality of adult mites was attained in A. calamus (2%) within 48 h of treatment. By 72 h, C. papaya (2%) and A. calamus (1%) also<br/>recorded 100 per cent mortality. Four days after treatment, A. marmelos (2%) and C. papaya (1%) also recorded significant mortality of adult mite, on par with these treatments, followed by A. squamosa (2%), B. monnieri (2%) and A. marmelos (1%). However, the methanol extracts did not record appreciable ovicidal activity. The botanical, A. calamus, found effective against the gravid females of T. truncatus based on the laboratory studies, was further subjected to bioassay guided fractionation, to identify the bioactive solvent fraction. Hexane, chloroform and methanol were employed as solvents based on the increasing order of polarity. Fractionated methanol extract at 0.7 per cent concentration resulted in 100 per cent mortality of eggs. All the three solvent fractions were promising against adult mites, recording 100 per cent mortality by 96 h. The efficacy of the methanolic fraction of A. calamus (0.3 and 0.5%) and aqueous extract of A. squamosa (7.5%) was evaluated along with neem oil emulsion (2%), horticultural mineral oil (HMO 2.5%) and spiromesifen (100 g a.i/ ha) against T. truncatus on cucumber, in polyhouse. Within seven days of treatment, 0.5 and 0.3 per cent A. calamus recorded significant per cent reduction in mite population closely following the synthetic acaricide, spiromesifen. By tenth day, A. calamus (0.5%) and spiromesifen recorded complete reduction in mite population. The lower concentration of 0.3 per cent also recorded mite population on par with these. These treatments were followed by A. squamosa and HMO, in reducing the mite population. Laboratory bioassay to evaluate the safety of the methanolic fraction of A. calamus to the predatory mite, N. longispinosus resulted in 100 per cent mortality of the adult. Evaluation of safety of the methanolic fraction of A. calamus to the acaropathogen, A. zeylanicum using poisoned food technique revealed antagonistic effect on the acaropathogen. The methanolic fraction caused 62.96, 54.07 and 40.37 per cent inhibition at concentrations of 0.7, 0.5 and 0.3 per cent, respectively. The study identified appreciable acaricidal property of the botanicals A. calamus, C. papaya, B. monnieri, A. squamosa, A. marmelos and L. camera against spidermites. The methanolic fraction of A. calamus emerged as a promising candidate in mite pest management under protected cultivation. |
