Research Expertise and Interest
environmental science, pest management, biological control of insect pests, ecology of insect parasitism, natural enemy biology, Epiphyas postvittana, Chromaphis juglandicola, Tetranychus species
Nicholas Mills is a professor of Environmental Science, Policy & Management, Division of Organisms & Environment. The focus of his research group is the biological control of insect pests and the ecology of insect parasitism and predation. Classical biological control has an outstanding history of success in the sustained regional control of invading pests and provides exciting opportunities for both lab and field-based ecological research. However, not all biological control introductions result in spectacular reductions of pest damage and so a major emphasis in their work is to address arguably one of the most challenging questions in biological control research: what are the determinants of success in classical biological control? In addition to classical biological control, the augmentation of natural enemy populations is an aspect of biological control that is rapidly gaining attention. The use of natural enemies as biological pesticides raises some very interesting questions about the performance characteristics of natural enemies, strategies for release and optimization of impact.
Natural enemies, and in particular insect parasitoids, are known not only for their importance in biological control but also as model systems for the analysis of many exciting questions in biology. As a result, their research interests include a variety of aspects of natural enemy biology, from behavior and evolutionary biology to population and community ecology through observational, experimental and comparative analysis. One of the most satisfying aspects of their work is the knowledge that the discovery of exciting new elements of natural enemy biology provides a direct linkage to the implementation of improved biological control and a reduced reliance on pesticide intervention in insect pest management.
Current Projects, Biology of Insect Parasitoids and Predators. The lifetime reproductive success of a female natural enemy is dependent on her ability to locate hosts, to assess the quality of each host, and to respond to variation in encounter rates and host quality. Thus parasitoids and predators are ideal model organisms for the study of behavioral ecology – how behavioral decisions influence the fitness or reproductive success of an organism. Current projects focus on dispersal, functional and numerical responses, population structure and hybridization, and a demographic approach to evaluating the compatibility of natural enemies with pesticides. They are currently working with Chrysoperla carnea, Galendromus occidentalis, Hippodamia convergens, Mastrus ridibundus, Trioxys pallidus, and Trichogramma species.
Dynamics of Biological Control Systems. Ecologists have not been slow to address biological control through ecological theory and the development of conceptual models to capture the essence of host-parasitoid interactions. The difference between success and failure in biological control can be due to exogenous limitations or to endogenous processes. They focus on the latter to find more general aspects of the interaction between natural enemies and hosts that can be used to improve success and minimize the risks of biological control. Current projects use simple models to examine the interplay of host population growth rate, host refuges from parasitism, parasitoid fecundity, and generation time ratios in the dynamics of host-parasitoid systems.
Implementation of Biological Control. They currently have three biological control projects in our laboratory, one on web-spinning spider mites (Tetranychus spp.) as secondary pests of walnut production; a second on the light brown apple moth (Epiphyas postvittana) a notorious urban invader in California; and a third on walnut aphid (Chromaphis juglandicola) a well-known pest of walnuts. The projects involve foreign exploration and selection of natural enemies for importation, field release and monitoring of natural enemies, analysis of population structure and abundance, and laboratory bioassays for selectivity of pesticides.