Effect of temperature on the life cycle of Harmonia axyridis (Pallas), and its predation rate on the Spodoptera litura (Fabricius) eggs

Abstract

Biological control is one of the strategies of pest control which is determined by the biological fitness and metabolic rates of the predator species used. Temperature and resource are important factors which influence the role of insects as biocontrol agents. Harmonia axyridis is a cosmopolitan and non-specific polyphagous predator. It can survive ecologically diverse environments and exploit multiple preys. This study investigated the effects of temperature on the population parameters of H. axyridis and its predation on the eggs of prey Spodoptera litura. For this purpose, an age-stage, two-sex life table of the predator was constructed at four constant temperatures, i.e. 15, 20, 25 and 30 degrees C, under laboratory settings of: 70 +/- 5% RH, and 16:8 h (L: D) photoperiod. A computer simulation was then used to project the population and predation responses with respect to temperatures tested. We found that the development of larvae and adult (male/female) stages of H. axyridis decreased with colder temperatures (i.e., 15 and 20 degrees C) but increased with warmer temperatures (25 and 30 degrees C). The intrinsic rate of increase (r) and mean generation time (T) were 0.0662 d(-1) and 79.84 d at 15 degrees C, 0.0843 d(-1) and 64.90 d at 20 degrees C, 0.1067 d(-1) and 48.89 d at 25 degrees C, and 0.1378 d(-1) and 35.55 d at 30 degrees C, respectively. The mean duration of the total pre-adult stage was 44.26, 32.91, 20.63, and 15.39 d at 15, 20, 25, and 30 degrees C, respectively. At 30 degrees C. the finite rate of increase (1.1477 d(-1)) was the highest and the mean generation time (35.55 d) was the shortest. The net predation rate (C-0) was 7935.54, 10,466.28, 10,139.38, and 7126.36 eggs at 15, 20, 25, and 30 degrees C, respectively. Population and predation projections were proportional to temperature. These findings are important for modelling the population responses of H. axyridis to climate change and tailoring integrated pest management strategies to altered climates.