Comparison of the life tables and predation rates of Harmonia dimidiata (F.) (Coleoptera: Coccinellidae) fed on Aphis gossypii Glover (Hemiptera: Aphididae) at different temperatures

Abstract

The life histories and predation rates of the ladybird beetle Harmonia dimidiata (F.) were compared among beetles kept at 15, 20, and 25 °C. The beetles were fed on Aphis gossypii Glover and were maintained at 70 ± 10% RH and a 14:10 (L:D) h photoperiod. According to the age-stage, two-sex life table, the net reproductive rates (R₀) were 147.4, 98.7, and 62.5 offspring for beetles kept at 15, 20, and 25 °C, respectively. Additionally, we employed both the jackknife and bootstrap techniques for estimating the means, variances, and standard errors of the population parameters. The sample means of R₀ and the other population parameters obtained using the bootstrap technique fit a normal distribution, but the jackknife technique generated biologically meaningless zero values for R₀. The net predation rates were 10963, 13050, and 7492 aphids for beetles kept at 15, 20, and 25 °C, respectively. For a comprehensive comparison of predation potential, we incorporated both the finite rate and the predation rate into the finite predation rate. When both the growth rate and the predation rate were considered, our results showed that H. dimidiata is a more efficient biological control agent for A. gossypii at 20 and 25 °C than at 15 °C.

Introduction

The melon aphid (Aphis gossypii Glover) is a global insect pest with a wide range of host plants, including the 84 species in 34 families that have been recorded in Taiwan (Tao, 1990). Infection by aphids causes the stunting or death of crops due to the sucking of sap, the secretion of honeydew that acts as a sooty mold medium, and the transmission of viral plant diseases (Chang et al., 1987, Escriu et al., 2000, Gildow et al., 2008).

According to Tao (1990), 34 arthropod species that are natural enemies of the melon aphid have been recorded in Taiwan. Among these, 17 species are ladybird beetles, with Harmonia dimidiata (F.) being a common example. Kuznetsov and Pang (2002) reported a daily predation rate of more than 200 A. gossypii for H. dimidiata (F.). They also observed that H. dimidiata (F.) can be kept in a refrigerator at 15 °C for 4 months without aphids and that approximately 90% of this population could survive on a 10% honey solution. H. dimidiata’s high voraciousness and ability to survive at low temperatures may make them a useful natural enemy for the purposes of biological control.

To successfully mass rear predatory natural enemies for biological control, it is necessary to determine their population characteristics, including growth rate, stage differentiation, fecundity, and predation rate. The key components for this type of evaluation are life table studies and assessments of predation rate. Only a life table can provide a comprehensive description of the species’ development, survival, and fecundity. A proper assessment of predation potential should include the evaluation of a life table. For most insects, the developmental rates vary among individuals and between the sexes (Istock, 1981, Chi and Liu, 1985, Carey, 1993). Chi and Liu, 1985, Chi, 1988 noted that neglecting the variable developmental rate and the male population may cause errors in calculating the age-specific survival rate and, consequently, result in errors in assessing the demographic parameters. Chi and Liu, 1985, Chi, 1988 developed an age-stage, two-sex life table that takes stage differentiation and the male population into consideration. The age-stage, two-sex life table has been used to describe the population characteristics of many insect and mite species under the influence of a variety of physical conditions.

The influence of a key abiotic external factor, temperature, on insect development has been studied extensively. Improving our knowledge of the effects of temperature on insect development will be helpful in the mass rearing of insects and their application as natural predators of pests. Previous works (Kuznetsov and Pang, 2002, Agarwala et al., 2009) have indicated that in terms of developmental time, fecundity, and functional response, the most favorable temperature for culturing H. dimidiata on A. gossypii is 20–25 °C. However, there is a lack of experimental life table data regarding the effects of temperature. In the present study, data regarding the life histories and predation rates of H. dimidiata fed on A. gossypii at different constant temperatures will be collected and analyzed based on an age-stage, two-sex life table that considers the variations in development and the predation rates among individuals and between the sexes. For the comparison of predators, we will use the finite predation rate to compare the predation potential of predators living under different conditions.