Efficacy of spiromesifen on Aceria litchii (Keifer) in relation to Cephaleuros virescens Kunze colonization on leaves of litchi (Litchi chinensis Sonn.)

Abstract

The phytophagous mite, Aceria litchii (Keifer), is one of the major pests of litchi (Litchi chinensis Sonn.) in Asia and Australia. By sucking on the cells of young leaves, the mites cause punctiform lesions. These are used by the parasitic alga Cephaleuros virescens Kunze to penetrate the leaf epidermis by forming a felt-like erineum. In the present study, significant positive relationships between mite density on algal infested leaves on the one hand and algal density and degree of erineum leaf cover on the other were found. In relation to these factors, the efficacy of different concentrations (0.036 g a.i. l−1, 0.072 g a.i. l−1 and 0.144 g a.i. l−1) and application frequencies (single and double) of spiromesifen, a lipid biosynthesis inhibiting agent, on the numbers of A. Litchii on litchi leaves was tested. Single spiromesifen applications significantly reduced numbers of mites per leaf by 34% at medium and by 77% at the highest concentration within 7 days after application. With double applications, numbers of mites were reduced by more than 80% at all concentrations 7 days after the second treatment. A complete elimination of A. Litchii was reached 18 days after the second application of the highest spiromesifen concentration. The degree of erineum cover and algal density did not significantly affect the efficacy of the double spiromesifen treatments, indicating that spiromesifen acts in a dose-dependent manner on A. Litchii.