PhD University of East Anglia, UK
Invasive species, Biological control, Population ecology, Entomology/Insect biology
The focus of my 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 our 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, our 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 our 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 ProjectsBiology 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. We are currently working with Chrysoperla carnea, Hippodamia convergens, Meteorus ictericus, Pediobius ni, 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. We focus on the latter to find more general aspects of the interactions 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. We currently have three biological control projects in our laboratory, one on the light brown apple moth (Epiphyas postvittana) a recent invader from Australia that is an important pest of grape vines and pome fruit; a second on the mealy plum aphid (Hyalopterus pruni) a key pest of prunes; and a third on walnut aphid (Chromaphis juglandicola) a well-known pest of walnuts. The first two projects involve foreign exploration, selection of natural enemies for importation, and field release and monitoring. The third project is designed to elucidate reasons for the localized failure of sustained biological control 35 years after the successful introduction of the parasitoid Trioxys pallidus.
Hogg, B. N., Wang, X.-G., Levy, K., Mills, N. J., and Daane, K. M. 2013. Complementary effects of resident natural enemies on the suppression of the introduced moth Epiphyas postvittana. Biological Control 64: 125-131.
Engelkes, T., and Mills, N. J. 2013. A fast-track for invasion: Invasive plants promote the performance of an invasive herbivore. Biological Invasions 15: 101-111.
Nelson, E. H., Hogg, B. A., Mills, N. J., and Daane, K. M. 2012. Syrphid flies suppress lettuce aphids. BioControl 57: 819-826.
Buergi, L. P., and Mills, N. J. 2012. Ecologically relevant measures of the physiological tolerance of light brown apple moth, Epiphyas postvittana, to high temperature extremes. Journal of Insect Physiology 58: 1184-1191.
Herrera-Reddy, A. M., Carruthers, R. I., and Mills, N. J. 2012. Integrated management of Scotch broom (Cytisus scoparius) using biological control. Invasive Plant Science and Management 5: 69-82.
Wang, X.-G., Levy, K., Mills, N. J., and Daane, K. M. 2012. Light brown apple moth in California: a diversity of host plants and indigenous parasitoids. Environmental Entomology 41: 81-90.
Engelkes, T., and Mills, N. J. 2012. A conceptual framework for understanding the success of arthropod predator and parasitoid invasions. In: Invasive Alien Arthropod Predators and Parasitoids: An Ecological Approach. Roy, H., De Clercq, P., Lawson Handley, L.-J., Sloggett, J. J., Poland, R. & Wajnberg, E. (Eds.), Springer, pp. 9-19.
Mills, N. J. 2012. Transient host-parasitoid dynamics illuminate the practice of biological control. Journal of Animal Ecology 81: 1-3.
Hopper, J. V., Nelson, E. H., Daane, K. M., and Mills, N. J. 2011. Growth, development and consumption by four syrphid species associated with the lettuce aphid, Nasonovia ribisnigri, in California. Biological Control 58: 271-276.
Engelkes, T., and Mills, N. J. 2011. A conceptual framework for understanding the success of arthropod predator and parasitoid invasions. BioControl 56: 383-394.
Cheng, R.X., Meng, L., Mills, N.J., and Li, B.P. 2011. Host preference between symbiotic and aposymbiotic Aphis fabae, by the aphid parasitoid, Lysiphlebus ambiguous. Journal of Insect Science 11(81): 1-13.
Lozier, J. D., and Mills, N. J. 2011. Predicting the potential invasive range of light brown apple moth (Epiphyas postvittana) using biologically informed and correlative species distribution models. Biological Invasions 13: 2409-2421.
Hogg, B. N., Nelson, E. H., Mills, N. J., and Daane, K. M. 2011. Floral resources enhance aphid suppression by a hoverfly. Entomologia Experimentalis et Applicata 141: 138-144.
Latham, D. R., and Mills, N. J. 2011. Effects of temperature on the life history parameters and population growth rates of Hyalopterus pruni (Hemiptera: Aphididae). Journal of Economic Entomology 104: 1864-1869.
Bürgi, L. P., Roltsch, W. J., and Mills, N. J. 2011. Abundance, age structure, and voltinism of light brown apple moth populations in California. Environmental Entomology 40: 1370-1377.
Stavrinides, M. C., and Mills, N. J. 2011. Influence of temperature on the reproductive and demographic parameters of two spider mite pests of vineyards and their natural predator. BioControl 56: 315-325.
Chaplin-Kramer, R., Kliebenstein, D., Chiem, A., Morrill, E., Mills, N., and Kremen, C. 2011. Chemically-mediated tritrophic interactions: opposing effects of glucosinolates on a specialist herbivore and its predators. Journal of Applied Ecology 48:880-887.
Herrera, A. M., Carruthers, R. I., and Mills, N. J. 2011. No evidence for increased performance of a specialist psyllid on invasive French broom. Acta Oecologia 37: 79-86.
Herrera, A. M., Carruthers, R. I., and Mills, N. J. 2011. Introduced populations of Genista monspessulana (French broom) are more dense and produce a greater seed rain in California, USA, than native populations in the Mediterranean Basin of Europe. Biological Invasions 13: 369-380.
Mills, N. J. 2010. Egg parasitoids in biological control and integrated pest management. In: Egg Parasitoids in Agroecosystems with Emphasis on Trichogramma. Postali Parra, J. R., Consoli, F. L., Zucchi, R. A. (Eds.), Springer, pp. 384-411.
Stavrinides, M. C., Lara, J. R., and Mills, N. J. 2010. Comparative influence of temperature on development and biological control of two common vineyard pests (Acari: Tetranychidae). Biological Control 55: 126-131.
Stavrinides M. C., Daane, K. M., Lampinen, B. D., and Mills, N. J. 2010. Plant water stress, leaf temperature and spider mite (Acari: Tetranychidae) outbreaks in California vineyards. Environmental Entomology 39: 1232-1241.
Gutierrez, A. P., Mills, N. J., and Ponti, L. 2010. Limits to the potential distribution of light brown apple moth in Arizona-California based on climate suitability and host plant availability. Biological Invasions 12: 3319-3331.
Bürgi, L. P., and Mills, N. J. 2010. Cold tolerance of the overwintering larval instars of light brown apple moth Epiphyas postvittana. Journal of Insect Physiology 56: 1645-1650.
Latham, D.R., and Mills, N.J. 2010. Life history characteristics of Aphidius transcaspicus, a parasitoid of mealy aphids (Hyalopterus species). Biological Control 54: 147-152.
Stavrinides, M. C., Van Nieuwenhuyse, P., Van Leeuwen, T., and Mills, N. J. 2010. Development of acaricide resistance in Pacific spider mite (Tetranychus pacificus) from California vineyards. Experimental and Applied Acarology 50: 243-254.
Latham, D. R., and Mills, N. J. 2010. Quantifying aphid predation: the mealy plum aphid Hyalopterus pruni as a case study. Journal of Applied Ecology 47: 200-208.
Mills, N. J., and Kean, J. M. 2010. Behavioral studies, molecular approaches, and modeling: methodological contributions to biological control success. Biological Control 52: 255-262.
Mills, N. J., and Latham, D. R. 2009. Quantifying the role of predation in the seasonal dynamics of aphid populations. Redia 92: 153-157.
Jones, V. P., Unruh, T. R., Horton, D. R., Mills, N. J., Brunner, J. F., Beers, E. H., and Shearer, P. W. 2009. Tree fruit IPM programs in the western United States: the challenge of enhancing biological control through intensive management. Pest Management Science 65: 1305-1310.
Mills, N. J. 2009. Parasitoids. In: Encyclopedia of Insects, 2nd edition (eds. Resh VH, Cardé R), pp. 845-848. Academic Press, San Diego.
Latham, D., and Mills, N. J. 2009. Quantifying insect predation: a comparison of three methods for estimating daily per capita consumption of two aphidophagous predators. Environmental Entomology 38: 1117-1125.
Lozier, J. D., and Mills, N. J. 2009. Ecological niche models and coalescent analysis of gene flow support recent allopatric isolation of parasitoid wasp populations in the Mediterranean. PLoS ONE 4(6): e5901. doi:10.1371/journal.pone.0005901
Stavrinides, M., and Mills, N. J. 2009. Demographic effects of new generation pesticides on biological control of Pacific spider mite (Tetranychus pacificus) by the western predatory mite (Galendromus occidentalis). Biological Control 48: 267-273.
Hougardy, E. and Mills, N. J. 2009. Factors influencing the abundance of Trioxys pallidus, a successful introduced biological control agent of walnut aphid in California. Biological Control 48: 22-29.
Lozier, J. D., Roderick G. K., and Mills, N. J. 2009. Molecular markers reveal strong geographic, but not host associated, genetic differentiation in Aphidius transcaspicus, a parasitoid of the aphid genus Hyalopterus. Bulletin of Entomological Research 99: 83-96.
Lozier, J. D., Roderick G. K., and Mills, N. J. 2009. Tracing the invasion history of mealy plum aphid, Hyalopterus pruni (Hemiptera: Aphididae), in North America: a population genetics approach. Biological Invasions 11: 299-314.
Honors and Awards
- University of California, Agriculture and Natural Resources, Distinguished Service Award - Outstanding Faculty, 1997
- University of California, Berkeley, College of Natural Resources, Distinguished Teaching Award, 2002
- University of California, Department of Environmental Sciences, Policy and Management, Award for Outstanding Mentorship of Graduate Students, 2012
- ESPM 44 - Introduction to Biological Control
- ESPM 113 - Insect Ecology
- ESPM 134 - Fire, Insects, and Disease in Forest Ecosystems