BioControl 46: 337–343, 2001. © 2001 Kluwer Academic Publishers. Printed in the Netherlands. Research Note Altered behavior and distribution of pea aphids, Acyrthosiphon pisum (Homoptera: Aphididae), infected with Pandora neoaphidis (Zygomycetes: Entomophthorales) M.A. JENSEN, J.E. LOSEY ∗ and A.E. HAJEK Department of Entomology, Cornell University, Ithaca, New York, USA ∗ author for correspondence; e-mail: JEL27@cornell.edu Received 9 June 2000; accepted in revised form 19 December 2000 Abstract. The distribution and mobility of infected aphid hosts can have a great effect on the ability of a pathogen to spread throughout a population. The distribution of dead and living pea aphids (Acyrthosiphon pisum) infected with Pandora neoaphidis was compared with that of their healthy conspecifics. Infected aphids were significantly more likely to be found on the undersides of alfalfa leaves and off of the plants than were healthy aphids. These two shifts in microhabitat location have potential costs and benefits for both the host and the pathogen. Key words: behavioral modification, distribution, migration, Acyrthosiphon pisum, Pandora neoaphidis Introduction Entomopathogenic fungi possess several qualities that make them exemplary for the biological control of aphids. These qualities include their effectiveness – both in the field and in the laboratory, their ease of culture in vitro, their high specificity towards particular species, and their generally low negative impact towards nontarget organisms (Latgé and Papierok, 1989). Pea aphids are pests of many legumes and important vectors of plant diseases (Patch, 1938). Pandora neoaphidis (Remaudiere and Hennebert) Humber is the most common pathogen of the pea aphid, Acyrthosiphon pisum (Harris), in the northeastern U.S. (Hutchison and Hogg, 1985). P. neoaphidis can substan- tially impact aphid population dynamics directly through epizootics (Latgé and Papierok, 1989) or indirectly through interactions with other natural enemies (Roy et al., 1998). To most effectively utilize P. neoaphidis as an agent for biological control of aphids, it is necessary to understand the biotic and abiotic conditions that facilitate the spread of infection.