Influence of ground cover on dynamics of Amblyseius fallacis Garman (Acarina; Phytoseiidae) in New York apple orchards

Abstract

Four studies were conducted between 1989 and 1992 to determine the influence of vegetation beneath apple trees on the dynamics of the mite predator Amblyseius fallacis (Garman). Withholding herbicide applications in the spring to allow ground cover to grow beneath trees did not result in greater numbers of A. fallacis in trees during the summer compared with plots where herbicides were applied and ground cover was greatly reduced. A survey of 23 commercial orchards revealed that A. fallacis overwintered on trees in many of these sites (14). Typhlodromus pyri (Scheuten) and Typhlodromus occidentalis (Nesbitt) were also found in the trees. In two of the orchards phytoseiids and European red mites, Panonychus ulmi (Koch), were sampled the following spring and summer. Amblyseius fallacis were found in the trees at bloom (10 May) and there was no evidence that they first increased in density in the ground cover and then colonized trees. Overwintering predator populations were repeatedly sampled in six orchards during autumn, winter, and spring 1991–1992. Amblyseius fallacis and T. pyri overwintered in high numbers in the trees. Amblyseius fallacis was also found in high numbers in the ground cover. Typhlodromus pyri also overwintered in the ground cover, but in lower numbers. Both predator species suffered high overwintering mortality, with that of T. pyri apparently less than that of A. fallacis. Treatment of ground vegetation with a pyrethroid insecticide in the spring did not affect arboreal A. fallacis densities during the summer; however, treatment of trees with the insecticide greatly reduced A. fallacis densities. In New York, ground cover in apple orchards directly beneath the trees does not appear to play a large role in the dynamics of A. fallacis.