Diversity and phenology of the predator complex in orchards

The increased use of mating disruption and reduced risk insecticides as substitutes for organophosphate insecticides in apple orchards of the western U.S. has led to associated increases in densities of generalist predators in orchards, as well as improved opportunities for biological control. Effective use of biological control in orchards requires information on numbers, types, and seasonality of generalist predators; information on seasonality is of particular importance for growers who wish to time insecticide applications so as to minimize effects of chemicals on natural enemies. During the 2008 and 2009 growing seasons, we sampled each of 8 organic or reduced risk apple orchards continuously over the interval between March and October. Numbers and types of tree-dwelling generalist predators were monitored at 4-7 day intervals using beating trays. Counts of generalist predators were very high in several orchards, with numbers dominated by spiders and Heteroptera. Species diversity was highest for spiders. Seasonality of predators was highly variable among species, and encompassed several life history strategies: single generation, multiple generations, overwintering adult, and overwintering immature. This variation substantially complicates efforts at developing insecticide programs in which predator phenology is included as a factor affecting spray decisions.