A. G. Selhime

Suppression of citrus rust mite populations with application of fragmented mycelia of Hirsutella thompsonii

Abstract Large quantities of mycelia of Hirsutella thompsonii , a fungal pathogen of the citrus rust mite, Phyllocoptruta oleivora , were produced by use of a submerged culture technique. The mycelia were then fragmented and applied as a foliar spray to orange trees infested with high populations of the citrus rust mite. The mycelia began to sporulate on the foliage about 48 hr after application. The mean number of mites per leaf decreased and the rate of mite infection increased at 1 week post-treatment. Mite populations remained at low levels for 10–14 weeks.

Biology of Entomophthora Floridana Attacking Eutetranychus Banksi

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.

The Feeding Behavior and Biology of Parapronematus Acaciae (Acarina: Tydeidae)

Although the tydeid mite, Parapronematus acaciae Baker, was previously reported as being a predator of the citrus rust mite, Phyllocoptruta oleivora (Ashmead), laboratory studies proved it was not a predator of P. oleivora, the citrus red mite, Panonychus citri (McGregor), or the Texas citrus mite, Eutetranychus banksi (McGregor). However, four complete generations of P. acaciae were reared on Penicillium digitatum Sacc. and Colletotrichum gloeosporioides Penzig, two common leaf-inhabiting fungi. One generation from egg to adult took approximately 15-18 days at a temperature of 25 @+ 2@* C. Larvae fed readily on the fungi, as did what appeared to be the two nymphal stages. Prospects for the biological control of the citrus rust mite are also discussed.

Agistemus Floridanus (Acarina: Stigmaeidae), A Predatory Mite, on Florida Citrus

The strawberry mite, Agistemus floridanus Gonzalez, is readily distinguished from related species on Florida citrus by its strawberry-like color and appearance, smooth dorsal scuta, and elongate, subequal, stout, tapered dorsal setae. It feeds readily on a number of different insects and mites, completes development and increases its population on at least 4 economically injurious pests of citrus, and completes a life cycle in less than 2 weeks at summer temperatures on an optimal host, Phyllocoptruta oleivora (Ashmead). Maximum populations of the predator normally occur during the winter and spring but can occur during the summer and fall. A. floridanus is quite sensitive to commonly used spray chemicals. It is neither consistently associated with nor consistently capable of reducing populations of any specific prey species. Despite its ability to feed and reproduce on important injurious citrus insects and mites in Florida, especially the citrus rust mite, A. floridanus does not appear to have a biological control potential on citrus in this area. It is possible that this failure to attain control potential is predicated either on sensitiveness to weather as indicated by variations in its seasonal history or on susceptibility to chemical toxicity. However, the long life cycle, low biotic potential, and broad adequate host range are also possible causal factors.

Further attempts to establish the weevil egg parasite, Tetrastichus haitiensis in Florida.

In a further attempt to establish Tetrastichus haitiensis Gahan, an egg parasite of the weevil, Diaprepes abbreviatus (L.), releases of laboratory reared stock were made during 1970 and 1971 at Apopka and West Palm Beach, Florida. Recovery efforts made periodically during 1970-73 failed to provide evidence of establishment.

Biological Studies on Paracheyletia Bakeri (Acarina: Cheyletidae)

The female of Paracheyletia bakeri Ehara was first described by Ehara (1962) on Hibiscus rosa-sinensis L. at Hokkaido University in Japan. In the United States, it is associated with certain Florida citrus insects and mites and has been found in the litter under Florida citrus trees and occasionally on citrus leaves infested with scale and mites. On several occasions, P. bakeri has decimated laboratory cultures of Tetranychidae and Tenuipalpidae (Muma 1964). Several studies were therefore made to obtain more biological information about this cheyletid and to establish its importance as a predator of spider mites that attack citrus. These included laboratory studies of the general biology and controlled experiments to determine the life cycle, food consumption, longevity, and fecundity of the species.

Development of Diaprepes Abbreviatus on Potted Citrus Seedlings

Adult Diaprepes abbreviatus (L.) were recovered from citrus seedlings 132 through 168 days after infestation of the plants with 0- to 24-hour old larvae. Pupae were recovered 98 through 238 days after infestation. The number of larval instars could not be determined from the frequency distribution curves of head capsule measurements.

Two Muscardine Fungi Pathogenic to Diaprepes Abbreviatus

In the laboratory, the fungus Metarrhizium anisopliae (Metschnikoff) Sorokin infected 6.7% of the adults and none of the larvae of the so-called sugarcane rootstalk borer weevil, Diaprepres abbreviatus (L.). In contrast, Beauveria bassiana (Balsamo) Vuillemin infected 92.7% of the adults within 7 days and 76.9% of the larvae within 12 days.