Seasonal occurrence and abundance of redlegged earth mite Halotydeus destructor (Acari: Penthaleidae) in annual pastures of southwestern Australia

Abstract

AbstractSeasonal occurrence and abundance of redlegged earth mite, Halotydeus destructor (Tucker), was measured by weekly sampling in grazed annual pastures near Keysbrook (1990–1992) and Narrogin (1991–1992) in southwestern Australia. Mites were active for 27 weeks from the late autumn (May) to mid-spring (October), completing three generations at approximately 8 week intervals. The summer is spent as diapause eggs in the cadavers of adult female mites. In 1991 and 1992, active H. destructor was on average twice as abundant at Keysbrook (mean 11,300 mites/m2), as at Narrogin (mean 6400 mites/m2). Three times more eggs were laid at Keysbrook than Narrogin (mean 8500 and 2900 eggs/m2 respectively). Rainfall at Keysbrook was twice that at Narrogin, and temperatures were higher. We suggest that the rate of oviposition was less at Narrogin, probably because of resource limitation. The mature adult sex ratio was female biased, but was lower at Keysbrook (0.669) than at Narrogin (0.813). Neozygites acaridis, a fungal disease, was detected in less than 4% of the population, mainly in adult mites in late spring. Rainfall and temperatures were lower in the spring of 1992 than 1991 at both sites. Pasture was grazed considerably shorter in the spring of 1992, and numbers of H. destructor were lower, but numbers of eggs laid in the two years were similar. We suggest that active mite mortality was greater in spring of 1992, probably due to lower relative humidity. There were fewer adult mites in spring, and fewer diapausing eggs in summer at both sites in 1992 (36,600 diapause eggs/m2) than in 1991 (148,000 diapause eggs/m2). It is proposed that controlling mites in spring should lead to lower numbers of diapause eggs in summer and of mites emerging in autumn.