Ecology and insecticidal susceptibility of mycophagous Illeis koebelei Timberlake (Coleoptera: Coccinellidae: Halyziini)

Abstract

This study was conducted to investigate ecology and insecticidal susceptibility of mycophagous ladybeetle, Illeis koebelei. Twelve species of plants infected with powdery mildew were surveyed as host of I. koebelei in Gyeonggi-do, Korea from 2010 to 2012. The pear tree, Pyrus ussuriensis var. macrostipes (Nakai), was the most preferred plant to I. koebelei. I. koebelei was found from early July to early November in pear orchards. There was no trace without fungal materials through finding the spores of powdery mildew in the gut of I. koebelei. All motile stages are obligate mycophagy, and the feeding potential is ranked as follows: fourth instar,<br/> II<br/> adults, third instar, second and first instar.<br/> Development experiment was conducted at eight temperatures, ranging from 15.4 to 39.5 °C. Development rates were well fitted with linear and nonlinear models. Lower developmental thresholds for egg, first instar, second instar, third instar, and fourth instar larva, pre-pupa, pupa, and total immature stage were estimated to be 3.6, 12.7, 12.1, 11.3, 11.3, 12.8, 14.7, and 14.2 °C, respectively. Their respective thermal requirements in degree days (DD) were 86.6, 16.0, 22.5, 30.2, 49.3, 14.5, 43.8, and 217.4DD, respectively. Survivorship was highest at 25.1 °C for immature. Oviposition experiment was conducted at nine temperatures, ranging from 15.4 to 35.3 °C. Mean fecundity ranged from 18.6 eggs at 29.3 °C to 205.3 eggs at 20.3 °C. It was well described by the extreme value function. Adult survival and cumulative oviposition rates of I. koebelei were fitted to a sigmoid function and a two-parameter Weibull function, respectively. Findings of this study provide basic information for ecology of I. koebelei. They can be used to optimize environmental conditions for mass-rearing and shipping, comparing optimal occurrence conditions between I. koebelei and powdery mildew, and forecasting phenology and population dynamics of I. koebelei in the fields. Bioassay was conducted to determine the relative toxicities of several pesticides used for cucumber production in Korea to I. koebelei and to provide a background for implementation of integrated powdery mildew management programs. Synthetic and environmental-friendly products used conventionally for the control of insect or<br/> III<br/> microbial pests on cucumber in Korea. Based on IOBC classification, three insecticides, bifenthrin + imidacloprid, acetamiprid + indoxacarb, acetamiprid + etopheprox are classified as having a Class 4 (harmful). Spiromesifen showed the low toxicity to the survival and the fecundity of I. koebelei when this chemical had been exposed to 3rd larva or newly emerged adult via feeding with cucumber powdery mildew. However, pyriproxyfen not only decreased the fecundity of female adult but also strongly prohibited from pupation. Many commercial biological or botanical pesticides can restrict the population of I. koebelei. However, Q pact (a.i. Ampelomyces quisqualis 94013), Top seed (a.i. Paenibacillus polymyxa AC-1), BT one (Bacillus thuringiensis) and Solbitchae (insecticidal microorganism) had no toxicity to I. koebelei when this chemical had been exposed to the third instar larva or newly emerged adult feeding with cucumber powdery mildew.