Life table of the parthenium beetle, Zygogramma bicolorata (Coleoptera: Chrysomelidae), under different environmental variables.
The present study was aimed to understand the patterns in the development, survival and mortality of the immature stages of parthenium beetle, Zygogramma bicolorata Pallister along with the behavioural patterns associated with them under different environmental variables. This may aid in the improved mass multiplication of this weed biocontrol agent. For the purpose, life table of Z. bicolorata, a defoliator and biocontrol agent of a parthenium weed, Parthenium hysterophorus L., was studied in the laboratory under environmental variables, like food, temperature, photoperiod and different wavelengths of light. Kappa value, as mortality indicator, was lowest when beetles at various life stages were fed on inflorescence of weed, followed by leaves and stem, while the generation survival was highest on inflorescence. Temperature significantly affected the mortality and survival rate of key life stages of the beetle. Kappa value was lowest when beetles at immature stages were reared at 27°C, followed by 30, 25, 20 and 35°C. The generation survival and survival rate followed the same pattern. Mortality was significantly influenced by different photoperiods and it was least with best generation survival at 14 L:10D (long day) followed by 12 L:12D (equinox), 10 L:14D (short day), 24 L:0D (continuous light) and 0 L:24D (continuous dark). In response to different wavelengths of light, Kappa value was lowest with highest generation survival under white light (broad spectrum), followed by yellow (λ=ca. 570 nm), blue (λ=ca. 475 nm) and red (λ=ca. 650 nm). Egg experienced highest mortality. The life stages of the beetle can be best reared under long day white light at 27°C feeding on inflorescence of parthenium. Mortality trend was rigidly and significantly stage-specific, showing an innate survival effect which was independent from the factors studied.