Lethal effect of Beauveria bassiana, Melarhizium anisopliae, and Paecilomyces fumosoroseus on the eggs of Tetranychus cinnabarinus (Acari: Tetranychidae) with a description of a mite egg bioassay system

Fungal biocontrol agents, including 10 isolates of Beauveria bassiana, Metarhizium anisophae, and Paecilomyces/fymosoroseus were bioassayed for their lethal effects on the eggs of the carmine spider mite, Tetranychus cinnaharinus. The eggs were naturally laid on detached fava bean leaves on agar in petri dishes at 25degreesC under a photophase of 12:12 L:D. Suspensions of aerial conidia produced on rice were sprayed onto the leaves, yielding three conidial concentrations (No. conidia/mm(2)) from low to high for each of the fungal isolates with 3 or 4 replicates (30-65 eggs/leaf or replicate) at each concentration. During a 12-day observation period after spray, the infected eggs shrunk in shape, then turned orange-brown for B. bassiana and P fumosoroseus or dark-gray for M. anisopliae, and eventually had outgrowths of the sprayed fungus when maintained under moist conditions. Egg mortalities caused by fungal infection varied over time but had no change from day 8 or 9 onward. Differences of the mortalities on day 9 were significant among the fungal species or isolates tested. Based on the LC50 estimates determined by the concentration-mortality relationships of all isolates from probit analysis, B. bassiana Bb2860 with an LC50 of 548 conidia/mm(2) was highly infectious to T. cinnabarinus eggs, followed by P. fumosoroseus Pfrl 16 (848 conidia/mm(2)) and Pfrl 53 (913 conidia/mm(2)). Two M. anisopliae isolates with LC(50)s of 1717 and 1985 conidia/mm2 were inferior to the three isolates. The other isolates were poor or very poor in ovicidal activity. Our results confirmed the ovicidal activity of the three fungal species and suggested the feasibility to search for more ovicidal isolates from fungal species that may serve as biocontrol agents against spider mites such as T cinnabarinus. The mite egg bioassay system developed in this study will be useful towards this goal. (C) 2004 Elsevier Inc. All rights reserved.