Biology of Entomophthora floridana Attacking Eutetranychus banksi

Abstract

During experiments designed to evaluate the biological control of the Texas citrus mite, Eutetranychus banksi (McGregor), in citrus groves, it was found that counts of these mites and the known biological-control factors present did not adequately explain population increases and decreases. There are several species of predatory mites and a fungus, Entomophthora floridana Weiser and Muma, known to attack the Texas citrus mite. Need to increase count accuracy by refinement of counting technique was indicated. Since methods of counting predators in host mite samples had been verified it was suspected that the error involved estimates of diseased host mites. A laboratory investigation demonstrated that this was true. When Texas citrus mites were cleared in hot lactic acid, fungus tissues and mite structures were sharply differentiated. This led to a rapid, accurate determination of the number of fungus-infected and noninfected mites. At this point, it became obvious that a more complete knowledge of the life cycle and life stages of the fungus would be necessary to differentiate it from adventitious and saprophytic fungi also found on and in the mites. Review of pertinent literature revealed the following: Fisher (1954) first recorded an Entomophthora sp. from Texas citrus mites, noting that it appeared to be different from the unidentified species that she (Fisher 1951) had reported attacking citrus red mites, Panonychus citri. In her 1951 paper, Fisher discussed gross manifestations of diseased mites and presented a general discussion of the life cycle of Entomophthora taken from Steinhaus (1949), Bessey (1950), and Fitzpatrick (1930). Other publications on Entomophthora in citrus spider mites merely listed the association (Muma, Selhime, and Denmark, 1961), or discussed and evaluated fungus-caused epizootics in two species of spider mites (Muma 1955, 1958). The present study was initiated to determine the infective stage and life cycle of, and the epizootiology of the disease caused by E. floridana in Texas citrus mites. Susceptibility of the citrus red mites and six-spotted mites, Eotetranychus sexmaculatus, to the fungus was also investigated.