Development and survival of brinjal shoot and fruit borer Leucinodes orbonalis Guenee (Crambidae: Lepidoptera) at constant and alternating temperatures

Abstract

Brinjal shoot and fruit borer (BSFB) Leucinodes orbonalis Guenee is a key pest of brinjal and a major constraint to its production in the Indian subcontinent. The influence of constant as well as alternating temperatures on the development and survival of the pest is not known. Also, no information is available on the thermal constant, development thresholds, and phenology for the insect. So, the development and survival of Leucinodes orbonalis were studied under laboratory conditions at five constant (15 ± 1, 20 ± 1, 25 ± 1, 30 ± 1 and 35 ± 1 °C) and six alternating temperatures (25:15, 30:15, 35:15, 25:20, 30:20 and 35:20 °C) with 70 ± 5% R.H. and photoperiod of 14:10 (L:D) h. Under the alternating temperature regimes, maximum and minimum temperatures were maintained in a cycle of 14 and 10 h, respectively. Transition from maximum to minimum temperature followed square waveform and was complete within 10 min. The rate of development of the egg, larval, pupal, and adult stages accelerated with increases in the levels of temperature. Survival of BSFB was highest at intermediate temperature levels (25-30 °C), and it started declining outside this range. The favourable range of constant temperature for the development from egg to adult stage was 20 ± 1–35 ± 1 °C, while all six alternating temperatures were conducive for complete development of the pest. The thermal constant (K) and lower developmental threshold (Tmin) determined from a linear regression analysis for the total development period were 435.39–530.66 DD and 5.69–14.63 °C, respectively. The non-linear models did not fit the data obtained from constant temperature studies, as they overestimated the temperature threshold for the pest. In the case of alternating temperatures, Tmin, Topt, and Tmax for the different developmental stages were in the range of 6.87–10.47 °C, 30.3–30.4 °C, and 41.96–42.31 °C, under Briere-1, Briere-2 and Kontodimas models. Our results provide a framework for forecasting the pest incidence in the field, thus helping in modulating management schedules and techniques to target the weak link in the life cycle of the pest.