PhD

The study entitled "Microbial consortium for the management of insect pests of bitter gourd" was undertaken in the Department of Agricultural Entomology at College of Agriculture, Vellayani during the period 2013 - 2018 with an objective to isolate and identify microbial pathogens of pests of bitter gourd, develop a microbial consortium, test its compatibility with new pesticide molecules and to evaluate the efficacy of the microbial consortium against major pests of bitter gourd. Important pests of bitter gourd viz. fruit fly, Bactrocera cucurbitae, pumpkin caterpillar Diaphania indica, epilachna beetle Henosepilachna septima and red pumpkin beetle Aulacophora foveicollis were monitored from bitter gourd fields in Thiruvananthapuram and Kollam districts. One entomopathogenic fungi from diseased epilachna grub and pumpkin caterpillar larvae and one phylloplane bacteria were isolated. Kotch's postulates were proved for both the fungi. Upon preliminary screening for pathogenicity to various pests of bitter gourd, the fungi showed infectivity only towards epilachna grubs and pumpkin caterpillar whereas, the bacteria was found to be infective to epilachna grub, pumpkin caterpillar and adults of red pumpkin beetle. The fungus from both the insects was identified as Fusarium verticilloides and the bacteria was identified as Serratia marcescens Pathogenicity studies were conducted using isolates of Metarhizium anisopliae (Ma4) Beauveria bassiana (Bb5) and Lecanicillium lecanii obtained from NBAIR, Paecilomyces lilacinus isolate (rrCC 6064), Beauveria bassiana isolate (rrCC 6063) and the indigenous isolates. The fungi M anisopliae and B. Bassiana were infective to all the test insects selected whereas the P. lilacinus was found infective only to pumpkin caterpillar and fruit flies. Lecanicillium lecanii was not infective to any of the test insects. M anisopliae was more virulent to the test insects compared to B. bassiana and reported a mortality of 93.54%, 82.5%, 45%, 5%, 25%, 61.05% respectively in B. cucurbitae adults, D. indica larvae, grubs and adults of H septima, adults of A. foveicollis and nymphs of L. australis seven days after treatment at a dose of 10 8 spores Lethargic movement followed by cessation of feeding was common symptom of mycosis in all the species. Bioassay was conducted against the adults of B. cucurbitae, H septima and A. foveicollis and the larvae of D. indica and H septima using M anisopliae (Ma4), B. bassiana (Bb5) and P. lilacinus (nCC 6064). The LC 50 values for M anisopliae were 1.55x10, 0.18X10, 1.56X10 and 4.70x10 spores mL- 1 respectively for adults of B. cucurbitae, D. indica larvae, grubs and adults of H septima, adults of A. foveicollis at seven days after treatment. With respect to B. bassiana, LC 50 values were 1.65x10, 1.20x10, 1.05X10, 5.48x10 and 2.94 x 10 spores ml respectiveiy was required for the adults of B. cucurbitae, D. indica larvae, grubs and adults of H septima, adults of A. foveicollis respectively. In vitro compatibility studies were conducted between the different entomopathogenic fungi viz. B. bassiana, M anisopliae, P. lilacinus and L. Iecanii. In dual cultures, colony growth of B. bassiana and M. anisopliae got locked at the point of contact after two weeks of inoculation leaving a space of 3 to 5 mm apart from each other. In dual culture combinations of B. bassiana with P. lilacinus and L. Iecanii and M anisopliae with P. lilacinus and L. Iecanii, the colony growth stopped at two weeks after inoculation and a space of 1.5 cm to 2 cm was observed between different fungi. The interactions between various microbes in-vitro is not necessarily an indicator of their in-vivo interactions. Hence in vivo studies were conducted to assess the effect different microbial combinations viz. M anisopliae with B. Bassiana (consortium 1), M anisopliae with P. lilacinus (Consortium 2) and B. bassiana with P. lilacinus (Consortium 3) on test insects. Laboratory evaluation of the fungal consortium showed that the mixtures of various fungi were more pathogenic to the test insects in comparison with the fungi using individually. The fungal consortium 1 (Ma4 +Bb5) was highly virulent to all the test insects and resulted in per cent mortality of 100, 100, 88.33, 36.67, 36.67 and 100 respectively for adults of B. cucurbitae, D. indica larvae, grubs and adults of H septima, adults of A. foveicollis and nymphs of L. Australis seven days after treatment. Talc based formulations of the consortium maintained the required standards of colony forming units in the formulation and retained bioefficacy against various test insects. Cfu at three months after storage was 0.83 x 10 7 and 7.23 x 10 7cfu g-1 respectively for room temperature and refrigeration. The components of the consortium I, B. bassiana and M anisopliae were tested for the compatibility with five insecticides commonly used for pest management in bitter gourd in order to evaluate the suitability of integrating the product with pesticides in pest management programmes. Compatibility of both the fungi was observed for the insecticide Chlorantraniliprole 18.5 SC 0.006 % . Field experiment was conducted in bitter gourd, variety Preethi to evaluate the talc based formulation of consortium I along with insecticide Chlorantraniliprole 18.5 SC and Malathion as check. The treatments were two application of Consortium I @ 35 g L -1, consortium followed by Chlorantraniliprole 18.5 SC 0.006 %, Chlorantraniliprole 18.5 SC 0.006 % followed by Consortium I @ 35 g L-1, two applications of Chlorantraniliprole 18.5 SC 0.006 % and two applications of Malathion and untreated check. Results showed that the treatment, consortium 1 followed by Chlorantraniliprole 18.5 SC 0.006 % effectively managed populations of D. indica (0.08 larvae /10 leaves) , H septima (0.11 grubs/ 10 leaves) and A. foveicollis (1.5 adults/ plant) at five days after treatment. The percentage infestation of fruits by B. cucurbitae also got reduced from 52.18 % during pre-treatment count to 9.13% after treatment and produced the highest yield of 14.53 t ha-1. To conclude, the fungal isolate which caused natural epizootic in epilachna grub and pumpkin caterpillar larvae was identified as F. verticilloides. A bacterium S. marcescens was obtained from the phylloplane of bitter gourd and found to be pathogenic to larvae of D. indica and grubs of H septima. The fungi B. bassiana and M anisopliae were pathogenic to all the test insects. The combination of both resulted in a higher mortality of the test insects and increased the speed of kill than when treated alone. However, in dual culture studies, the fungi were incompatible. Talc based formulation of the consortium maintained the required standards of cfu in the formulations and efficacy upto three months after storage. Highest mortality of the test insects were noticed at the dose 40 g L -1 of the formulation. In the field study, consortium 1 (Ma4 + Bb5) followed by Chlorantraniliprole 18.5 SC 0.006 % was effective in managing the insect population and resulted in a high yield.