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The current study entitled “Efficacy of chitin enriched formulations of
Lecanicillium spp against sucking pests of rice Oryza sativa L. was carried out at
College of Agriculture, Vellayani and Integrated Farming Systems Research Station,
Karamana, Thiruvananthapuram, during 2015-17. The objective was to evaluate the
efficacy of chitin enriched formulations of Lecanicillium spp against sucking pests of
rice and to assess their impact on natural enemies. The species evaluated were the
indigenous isolate Lecanicillium saksenae (Kushwaha) Kurihara and Sukarno
(Accession No. LsVs 1 7714) and the NBAIR Isolate of Lecanicillium lecanii
(Zimmermann) Zare and Gams, (Vl 8).
The indigenous isolate, L. saksenae was found to be infective to rice bug
Leptocorisa acuta (Thunberg), brown planthopper Nilaparvata lugens (Stal), green
leafhopper Nephotettix nigropictus (Stal), white leafhopper Cofana spectra (Distant),
and white winged planthopper Nisia nervosa (Motschulsky). The exotic species
L. lecanii was infective to the hoppers but not to rice bug. The pentatomid bugs
Scotinophara coarctata (F.) and Menida versicolor (Gmelin) were not susceptible to
Lecanicillium spp. Symptoms of mycosis in hoppers which were similar in both the
fungi included inactivity, cessation of feeding in dying insects and growth of white
fluffy mycelia in the cadaver. The repeated tremors and convulsions were observed
in rice bugs treated with L. saksenae within 14 h, which might be due to the action of
toxic metabolites.
Cross infectivity studies to non target organisms revealed that L. saksenae was
found to be safe to the predatory coccinellids viz., Micraspis discolor (F.) and
Coccinella transversalis F., the mirid bug, Cyrtorhinus lividipennis Reuter, the
carabid beetle, Ophionea nigrofasciata Schmidt-Gobel, and the predatory spiders
Tetragnatha maxillosa (Thorell) and Oxyopes shweta Tikader, when treated with
spore suspension of 109 spores mL-1. Leaf and soil inoculation of the fungus @ 109
spores mL-1 did not show any cross infectivity to rice plants.
Laboratory experiment to determine the effective dose of the selected fungi
revealed that, spore suspension @107 and 108 spores mL-1of L. saksenae, caused 100
per cent mortality of L. acuta at 48 - 72 hours after treatment (HAT). Similar trend
was observed in the case of the hoppers, N. nigropictus, N. nervosa and C. spectra,
but for N. lugens it took 96 - 120 h. In the case of L. lecanii, @ 108 spores mL-1, 100
per cent mortality of N. lugens adults was recorded at 168 HAT, while only 76.67 per
cent died in 107 spores mL-1 during the same time period. The time taken was
extended upto 168 h for other hoppers.
Comparison of median lethal
concentration values of L. saksenae and
L. lecanii on the sixth day after treatment, revealed that L. lecanii needed a tenfold
increase in spore concentration (10 5spores mL-1), in all the susceptible insects,
indicating higher virulence of the indigenous isolate. Lethal concentration to cause
90 percent mortality values further substantiates the improved virulence of
L. saksenae (105spores mL-1), while for L .lecanii the value was hundred times higher
(107spores mL-1). The LT50 of L. saksenae was 18.58 h and 17.58 h for adults and
nymphs rice bug.
Field evaluation of the bioformulations revealed that, chitin enriched
formulation of L. saksenae was superior in terms of population of rice bug (1.33 bugs
per five sweeps and five random hills plot-1) and yield (3.25 kg plot-1, plot size 2 x 2
m). Though the talc formulation of Metarhizium anisopliae (Metschnikoff) Sorokin
was equally effective in reducing the population (1.67) there was no significant
increase in yield (2.17 kg plot-1). Population of insect predators, viz. coccinellids,
mirids, and reduviids did not vary significantly on third, seventh and fourteenth day
after first spray and third and seventh day after second spray among the treated and
untreated plots, the average population ranging from 0.67 to 4.67 per plot,. However,
the population was significantly low (1.67, 1.33, and 1.00) in plots treated with
Malathion 0.1% on the tenth day after first spay and tenth and fourteenth day after
second spray. The count of predatory spiders and hymenopteran parasitoids did not
vary significantly among the various plots throughout the experimental period.
The study indicated that the indigenous isolate, L. saksenae is more virulent
than the exotic isolate L. lecanii. Though L. lecanii could control the hopper pests in
rice, it is non infective to the major pest, rice bug, which is effectively managed by
chitin enriched formulations of L. saksenae. It is safe to natural enemies of rice
ecosystem and non infective to rice plant. Hence, it can be an effective contender and
suitable replacement to chemical pesticides for the management of sucking pests in
rice.