The studies on population management of chickpea pod borer, Helicoverpa armigera (Huebn) using pheromone traps over a period of 16 years (1983 to 1998) revealed peak adult populations from 20 March to 23 April. Among the environmental factors (maximum and minimum temperature, rainfall, wind speed and relative humidity), maximum and minimum temperatures were observed to be the most important environmental factors determining the population build up of this insect. The most favourable maximum and minimum temperature ranges for 80 to 90% trap catch populations were 16 to 35°C and 10 to 20°C respectively).
Regression analysis of mean 16 years pooled trap catch populations to ascertain relationship between the trap catch population and environmental factors indicated that, 1) Maximum and minimum temperatures were found significant at 15 day mean (R2=0.5948, p<0.05, d.f.=6) and at 14 day mean (R2=0.5939, p<0.05, d.f.=6) respectively, 2) Rainfall and wind speed showed significance at 2 day mean (R2=0.049, p<0.05, d.f.=65), and at 5 day mean (R2=0.2119, p<0.01, d.f=24) respectively, 3) Relative humidity (%) were found significant at 14 day mean at 0900 h (R2=0.5151, p<0.05, d.f.=6) and at 6 day mean at 1600 h (R2 =0.1739, p<0.05, d.f.=19) respectively. Stepwise multiple regression analysis of environmental factors with trap catches revealed that one or more than one environmental factor(s) showed significant influence on trap catches in different year.
Relationship between chickpea crop phenology and insect infestation (from 1994 to 1998) revealed that peak oviposition was observed between 01 and 18 April at 60 to 100% flowering stage of the crop. Peak populations of 1sti and 2nd instar larvae were noted between 07 and 23 April at 40 to 100% flowering of the crop and between 15 to 28 April at 100% flowering to 80% small podding stage crop respectively. The Infestation peaks of 3rd and 41h instar larvae were observed between 15 April and 03 May at full podding stage and between 20 April and 14 May at 15% crop maturity respectively. Maximum infestation of 51h instar was noted during 23 April to 10 May at 50% crop maturity. Significant regressions for H. armigera adults populations were obtained with the number of eggs planr1, number of 1st and 2nd instar larvae plan-1.
Chickpea pod borer, H. armigera infestation prediction models revealed that 04 March ± 6 days, 13 April ± 4 days and 07 June ±t 16 days were calculated to be the predicted dates for start, peak and end of trap catch populations respectively according to Calendar date method. Similarly, Degree-day accumulation method, 181.2 ± 39.7, 480 ± 85.5, and 1379.6 ± 319.3 degree-days were calculated as to be the predicted degree-days for start, peak and end of trap catch populations respectively. In April 1999, insect peak population was seen on 14 April (fallen in agreement within the range of the calendar date model) and accordingly the plant protection measures were adopted.
Significant synergistic interactions were observed in most of the combinations of HD-1-S-1980 with malic acid. The LC500f HD-1-S-1980 decreased with 1.0,2.0, & 4.0 % malic acid. Potency of HD-1-S-1980 was increased by 0.4, 2.7, and 12.89 folds in 1.0, 2,0, and 4.0 % malic acid combinations respectively. The bioassay results on susceptibility of different larval instars indicated that LC50s 42.2, 37.4, 40.9, 44.6, 59.9 ~g/ml diet for early & late 1 s" early & late 2nd and early 3rd instars respectively were significantly less from the LC50s of early and late 4th instar (99.1 and 119.9 ~g/ml diet respectively). DiPel 2X@ showed the lowest LC50 (21.0 ~g/ml) and the highest potency (52,000 IU/mg) and relative potency (3.20) in comparison with the LC50s of the other microbial insecticides DiPel ES@, MVP@, and Echotech Pro@.
Potted chickpea plants treated with DiPel 2X @ 0.8 Kg (25.6 BIU) and 1.6 Kg (51.2 BIU)/hectare caused 66.60 and 81.48% larval mortalities respectively and DiPel ES@ 2.00 liters (35.2 BIU)/hectare caused 84.0% larval mortality of H. armigera .
Field tests of DiPel 2X@ with and without adjuvants for control of chickpea pod borer for 3 successive years (1993-94 to 1995-96 chickpea seasons) resulted in significant increase in grain yield in DiPel 2X@ treatments as compared to the grain yield in control plot. The grain yield in DiPel 2X@ treatments (@ 1.6 Kg/hectare) was 2 to 3 times higher (511 to 1535 Kg/hectare) as compared to control plot yield (171 to 591 Kg/hectare). Chemical insecticide treatment (Karate 2.5 EC @ 0.500 ml/hectare gave higher grain yield (935 to 1892 Kg/ha) as compared to DiPel 2X@ treatments.