Post-release survey to assess impact and potential host range expansion by Amitus hesperidum and Encarsia perplexa, two parasitoids introduced for the biological control of the citrus blackfly, Aleurocanthus woglumi in Dominica
The citrus blackfly Aleurocanthus woglumi Ashby (Homoptera: Aleyrodidae), a native of South East Asia, was first reported in Trinidad in 1998. As part of a classical biological control programme against the pest, releases of Amitus hesperidum Silvestri (Hymenoptera: Platygasteridae) were made in Trinidad from June to August 2000. Field studies were conducted on three commercial citrus farms, two large estates ( >500 ha) and one small orchard (<50 ha) where releases were initially made. Adult blackfly and Amitus populations were monitored weekly with yellow sticky traps. Immature blackfly and parasitism rates were monitored monthly by field sampling. During the study period, citrus blackfly populations declined by more than 98% at all sites while parasitism increased to 60–90%. There were, however, differences between locations, with control at Cumuto being reached within 4 months, at Todd’s Road between 6 and 7 months and at La Gloria about 13 months. This was consistent with the parasitism rates recorded. Although Encarsia perplexa Huang and Polaszek (Hymenoptera: Aphelinidae) was also introduced, it would seem that A. hesperidum was capable of bringing down and maintaining citrus blackfly populations at acceptable levels by itself.