VIEW ARTICLE

Vector Relations

Role of the Leafcutter Bee in Dissemination of Verticillium albo-atrum in Alfalfa. H. C. Huang, Plant pathologist, Agriculture Canada Research Station, Lethbridge, Alberta, Canada T1J 4B1; K. W. Richards(2), and E. G. Kokko(3). (2)(3)Entomologist, and electron microscopist, Agriculture Canada Research Station, Lethbridge, Alberta, Canada T1J 4B1. Phytopathology 76:75-79. Accepted for publication 5 August 1985. Copyright 1986 The American Phytopathological Society. DOI: 10.1094/Phyto-76-75.

An investigation of the role of the alfalfa leafcutter bee (Megachile rotundata) as a dispersal agent for Verticillium albo-atrum was carried out in a commercial field of alfalfa known to have Verticillium wilt. Results showed that the bees use leaf pieces from both healthy and diseased plants to construct brood cells. Isolations from 69 female bees foraging in the field showed that 30% of the bees were contaminated with V. albo-atrum. Conidia were present in cuticle depressions of the abdomen, around the mouth, and on various other parts of the body. Alfalfa pollen grains covered with an amorphous mucilaginous substance were often adherent in these locations. On some bees, the conidia had germinated and developed into hyphal mats intermingled with pollen grains. Many of the pollen grains were colonized by hyphae. V. albo-atrum was isolated from remnant stigmata and styles of seed pods harvested from plants near the hive. Incidence of infected pods was 1.7% from plants with symptoms and 2.1% from symptomless plants. The alfalfa leafcutter bee is potentially an important agent for dissemination of V. albo-atrum because it utilizes diseased leaf tissue for making brood cells, carries the pathogen on its body, and transports the pathogen to infection courts such as pollen grains and stigmata of alfalfa flowers.