Microarthropods in australian sugarcane soils: A survey with emphasis on the Mesostigmata as potential regulators of nematode populations

Sugarcane is attacked by a suite of nematode pests, but little is known of the mites and other soil microarthropods that feed on them. To address this deficit, we undertook a survey of the soil microarthropod fauna in 60 sugarcane fields in Queensland, Australia. The results showed that oribatid mites and springtails dominated the upper 10 cm of sugarcane mineral soils. Laboratory observations demonstrated avid nematophagy in Galumnidae (Galumna sp., Pergalumna sp.), Scheloribatidae (Scheloribates sp.), and one unidentified Isotomidae (Collembola). Mesostigmata, a group of mites with many known nematophages, were never very abundant. Most of the taxa identified were previously known from Australia, but Protogamasellus sigillophorus Mineiro, Lindquist and De Moraes is reported for the first time and was reared through several generations on nematodes. In addition, we reared ten other cane field mesostigmatans on nematodes: Antennolaelaps sp., Asca garmani, Asca major, Cheiroseius sp., Cosmolaelaps sp., Gaeolaelaps sp., Gamasellodes bicolor, Gamasiphis sp., Holaspulus tenuipes, Protogamasellus mica. Because Mesostigmata were present at higher population densities in mineral soil where a mulch layer was retained after harvest, we assessed the effect of mulching in two sugarcane fields. Mulching did not result in significant differences in total microarthropods in the upper 5 cm of mineral soil. However, the mulch contained large numbers of free-living nematodes and 10% of the microarthropods were nematophagous mites. Results from a pot experiment also suggested that differences in soil properties affect nematophagous mite communities. More microarthropods and greater numbers of Mesostigmata were recovered from a well-structured clay loam soil than a sandy loam soil, and populations were highest in surface soils with high carbon contents and high levels of microbial activity.