Influence of temperature on the development and reproduction of Spodoptera litura (Fabricius) on castor bean: implications for its use as a trap crop

Climate change (rise in temperature, CO2 level, etc.) poses a serious threat to the agriculture sector. Therefore, it is necessary to develop and adopt new methods to cope with climate change. The army worm, Spodoptera litura (Lepidoptera: Noctuidae) is a destructive pest of many crops including castor bean in tropical regions of the world. The insect’s development, reproduction, food uptake, and body size on castor bean was assessed at five constant temperatures (15, 20, 25, 30, and 35 °C). Green Lacewing, Chrysoperla carnea (Stephens) (Neuroptera: Chrysopidae) is an important general predator. The predation rate dependency on temperature is also a concern in scenarios of climate change. Therefore, we studied predation by C. carnea at similar constant temperatures on eggs (with hairs and without hairs) and first instar larvae of S. litura. Immature stages of S. litura complete their duration at 15 to 35 °C. Optimum survival of all immature stages ranged from 25 to 27 °C according to polynomial survival model. There was no egg laying by S. litura at 15, 30, and 35 °C but a maximum of eggs (5212 eggs/female) were laid at 25 °C. The larval instar’s length did not follow temperature size rule, but pupal weight did. Only third and fourth instars of S. litura significantly increased their diet consumption at the warmest temperature (35 °C). The lower developmental threshold of all immature stages ranges from 10 to 11 °C, calculated by linear model. Non-linear mathematical models were used to calculate the upper developmental thresholds for larvae, pre-pupae, and pupae ranges which range from 39.3 to 43.0 °C. The predation rate of C. carnea increased with the increase in temperature from 15 to 35 °C, and more eggs without hairs, and first instar larvae of S. litura, were consumed than eggs with hairs. The suitability of castor bean as a host for mass rearing of S. litura is evident from our results at 25 °C. The study demonstrates the potential use of C. carnea to control S. litura on castor bean. We also discuss our results in context of the potential of castor bean as a trap crop for S. litura.