A laboratory evaluation of the repellency of Metarhizium anisopliae conidia to Coptotermes lacteus (Isoptera : Rhinotermitidae)

An agar-tube method for quantifying the repellency of different isolates of Metarhizium anisopliae to Coptotermes lacteus termites is described. Twent y grams of moist sand is placed firmly in the base of a 50ml plastic centri fuge tube and 2% water agar poured to the 45ml mark. The sand is mixed with a conidial suspension to assess the effect of concentration and isolate on repellency. A group of 50 workers and 10 soldier termites is placed on top of the agar, together with a small folded strip of filter paper, and the c ap replaced loosely. In the control tubes, the absence of repellency was sh own by termites tunnelling down through the agar and sand to the base of th e tube within 2 days, and then continuing to forage in the sand substrate, transferring sand into the agar tunnel and up to the surface of the agar. T wenty four isolates of M. anisopliae and one isolate of Beauveria bassiana were tested at a single dose of about 3 x 107 conidia/g of the sand substra te. Several isolates such as FI-610 were highly virulent and highly repelle nt, most tunnels reaching only a very short distance into the sand substrat e even after 7 - 14 days incubation. In addition, termites often retreated from the substrate after initial contact and sealed off tunnels by plugging with sand or agar, thereby preventing further contact with the substrate. Isolates such as FI-1037, FI-1099 and FI-1186 were markedly less repellent, termites tunnelling as rapidly as in the controls, then staying in the san d substrate and being eventually killed by the fungus. Other isolates did n ot exhibit repellency but also showed little virulence. The method is usefu l for comparing repellency of isolates and also for comparing different for mulations as part of a project to develop M. anisopliae for termite managem ent using a baiting strategy.