Prevalence of Erynia neoaphidis (Entomophthorales: Entomophthoraceae) Infections of Green Peach Aphid (Homoptera: Aphididae) on Spinach in the Arkansas River Valley

Abstract

Spinach, Spinacia oleracea L., produced for processing in the Arkansas River Valley of western Arkansas was sampled for live and diseased aphids from 1990 to 1993. The green peach aphid, Myzf.lS persicae (Sulzer), was the only aphid detected and its occurrence was highly variable. No aphids were detected in 14 of the 24 sampled fields. Nine of the 10 fields in which aphids were detected had individuals infected with the fungus Erynia neoaphidis (Remaudiere & Hennebert). No other fungal pathogens were observed. Infected aphids were detected in each of the 3 spinach production seasons (fall, winter, and spring). In several fields, especially during the winter of 1992, aphid populations declined with increased E. neoaphidis incidence. However, in fields with relatively high numbers of aphids this population decline occurred at or after the normal spinach harvest period. Aphids killed by E. neoaphidis were tightly held to spinach foliage and, when epizootics occurred at harvest, the spinach was rejected by the processor due to difficulty in washing the aphid cadavers from the product. KEY WORDS Myzf.lS persicae, Erynia neoaphidis, spinach THE GREEN PEACHAPHID, MyZU8 persicae (Sulzer), is the most abundant insect pest of spinach, Spinacia oleracea L., produced in the Arkansas River Valley of western Arkansas and eastern Oklahoma. Although aphids may be detected on fall-, winter-and spring-produced spinach, populations typically are highest on overwin-tered spinach harvested in early spring. Aphid populations in the Arkansas River Valley seldom reach sufficient levels to reduce spinach yields. Much concern exists, however, with the presence of aphids at harvest. The broad and crinkled leaves of spinach make removal of aphids during processing exceedingly difficult. Because aphid parts in processed spinach result in consumer complaints and litigation, entire spinach fields may be rejected by the processor if aphids are detected at harvest (McLeod 1989). Efforts at managing green peach aphids on spinach have been limited to foliar sprays of mevinphos or dimethoate. Neither has provided acceptable levels'of aphid suppression and registration of mevinphos on spinach was recently canceled. Much interest exists in developing alternatives for managing aphids on spinach. Efforts at breeding spinach resistant to aphids have been initiated with limited success (McLeod et al. 1991). Conservation of beneficial insects also has been suggested but has met with limited success because of low activity during cold weather. The ento