Background The tomato pinworm Tuta absoluta (Meyrick) (Lepidoptera: Gelechiidae) is one of the key pests of tomato worldwide, causing an estimated crop loss of 80 to 100%. This pest has developed resistance to several pesticides due to overuse, resulting in control failures in the field. The use of biological insecticides as Bacillus thuringiensis that expressed insecticidal proteins can be an alternative tool by insecticides to suppress the pest population. Main body Laboratory study investigated the efficacy of standard Bacillus thuringiensis (Bt) strains (4D1, 4D4, 4G1, 4K5 and 4XX4) against T. absoluta. Bioassay was conducted using tomato leaf discs treated with spore crystal lysates prepared from the standard strains, and mortality data was subjected to concentration-mortality probit analysis. The LC50 values for Bt 4D1, Bt 4D4 and Bt 4G1 were 6.10, 6.62 and 8.18 μg/ml for the 2nd instar; 9.90, 10.20 and 11.12 μg/ml for the 3rd instar; and 19.82, 23.16 and 24.54 μg/ml for the 4th instar, respectively, while the Bt 4K5 and Bt 4XX4 were not toxic to T. absoluta. Conclusion This study suggests that Bt strain 4D1 is effective against different larval instars of the pest and can be used in its management.

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The tomato pinworm, Tuta absoluta (Meyrick) (Gelechiidae: Lepidoptera), is an introduced serious pest of tomato in India. Management of this insect pest mainly relies on insecticides because of its high infestation levels on all plant parts and life stages of tomato crop. This laboratory study investigated the efficacy of Cry1Ac protein of Bacillus thuringiensis against T. absoluta. The LC 50 and LC 95 values for 2nd, 3rd, and 4th larval instars were 0.12, 0.27, and 0.43 μg/ml and 0.63, 0.71, and 2.64 μg/ml, respectively. Experimental results showed that Cry1Ac is effective against different larval instars of tomato pinworm.

To evaluate the effect of four silicon fertilizers, field experiment was conducted in farmer's holding at Poovanthi village of Sivagangai district, Tamil Nadu during 2017-2018 against sugarcane leaf hopper, Pyrilla perpusilla Walker and its parasitoid, Epiricania melanoleuca (Fletcher). Silicon fertilizers were applied @ 500 and 1000 kg ha-1 before planting and the leaf hopper population was recorded at 150, 180, 210, 240 and 270 days after application. The results of field experiment revealed that Pyrilla population was minimum in the plots treated with calcium silicate @ 1000 kg ha-1 (8.20 numbers/leaf) followed by calcium silicate @ 500 kg ha-1 (8.80 numbers/leaf) as compared over untreated check (98.20 numbers/leaf) and the percent reduction over untreated check was 82.45 and 73.71 per cent, respectively. Similarly, the per cent parasitism was maximum in the treatment with calcium silicate @ 1000 kg ha-1 (82.33%) during November, which was on par with untreated check. Hence, Pyrilla population declined to an extent of 82.45 per cent by enhancement of E. melanoleuca parasitism (82.33 %) due to the application of silicon fertilizers.

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