Observations on the Biology and Control of the Hawthorn (Two-Circuli) Mealybug, Phenacoccus Dearnessi (King)

Abstract

The hawthorn (two-circuli) mealybug, Phenacoccus deamessi (King), is a serious woody plant pest of hawthorn, Crataegus spp.) in Colorado. With the expanded use of this plant in landscape settings, P. deamessi has become of more economic importance. Studies were conducted to better understand its biology and to evaluate management strategies. In the area of Fort Collins, Colorado, nymphs emerged from overwintering sites on trunks and began spring activity on 20 March 1998. Migration to twigs was first noted on 14 April, peaking in early May and ceasing at the end of the month. Adult females first produced living young on 27 May and continued to reproduce until 14 October. Three species of predaceous lady beetles—Adalia bipunctata (L), Coccinella septempunctata (L), and Hippodamia convergens (Guerin-Meneville)—were observed feeding on P. deamessi nymphs as they emerged from overwintering sites, but predation of mature females was not observed; no parasitoids have been observed. There is a range of susceptibility to this insect among Crataegus spp.: Crataegus phaenopyrum 'Cordata' has remained highly resistant to infestation throughout this study; Crataegus x mordenensis 'Snowbird', C. succulenta macracantha, and C. ambigua also showed substantial levels of resistance. A wide range of insecticides has been evaluated for control, with imidacloprid (Merit) and permethrin (Astro) among the most effective. In addition, the use of horticultural oil consistently improved performance. However, timing of application seems to be critical; applications coinciding with migration of the overwintered nymphs to the twigs being particularly effective.