Effects of Verticillium lecanii (Zimm.) Viegas on Toxoptera citricida Kirkaldy (Homoptera: Aphididae) and its parasitoid Lysiphlebus testaceipes Cresson (Hymenoptera: Braconidae)

Abstract

The preponderance of susceptible sour orange (Citrus aurantium L.) rootstock has facilitated the spread of Citrus tristeza virus (CTV) in Trinidad and Tobago. CTV is transmitted by the brown citrus aphid Toxoptera citricida (Kirkaldy), which establishes large colonies on new flushes of citrus plants. As the colonies become highly populated, winged (alate) aphids are produced which can migrate to uninfected neighbouring citrus trees and hence transmit CTV. In the present study different concentrations of the entomopathogenic fungus Verticillium lecanii (Zimm) Viegas in water-based formulations were applied to T. citricida and the pathogenic effects were analysed. Bioassays were also conducted on the major parasitoid Lysiphlebus testaceipes Cresson to test the pathogenic effects of V. lecanii on mortality and the percent emergence from mummies. The LC₅₀ values for T. citricida and L. testaceipes were 2.26 × 10¹⁰ spores/ml and 1.09 × 10⁹ spores/ml, respectively. Statistical analyses indicated that there was no significant difference between the two LC₅₀ values. At the highest concentration (1.49 × 10⁹ spores/ml) percent mortality peaked at 78.9% after 12 days and 1.95 × 10⁹ spores/ml, mortality of L. testaceipes reached 95.1% after 6 days. Emergence of L. testaceipes at the highest concentration of 1.95 × 10⁹ spores/ml was 57.8%.