Biological and ecological studies of two spotted spider mite (Tetranychus urticae Koch) and its control on hops in Tasmania

摘要

This study was initiated in March 1987 and completed in March 1989.udAspects of the general biology and ecology of Two Spotted Spider Miteud(TSSM), Tetranychus urticae Koch, and its natural enemies in hop fieldsudwere investigated in the years 1987-88 and 1988-89. The investigation foundudthat TSSM overwinters in hollow cavities of hop twigs in the litter aroundudhop rootstocks. In late August to early September TSSM becomes active toudlay eggs and progressively colonizes hop on the lower surface of hop leaves.udThe teneral female mites of new generations were found to move upwardudwith elongation of hop vines.The distribution patterns of the mites on hopsudvary with time and mite stage. In early or mid-March, mites moveuddownward along hop vines to seek overwintering refuges. ududThe native predatory mite, Amblyseius longispinosus (Evans), wasudfound to overwinter in the litter around the hop base. While the importedudpredatory mite, Phytoseiulus persimilis Athias-Henriot, cannot survive theudTasmanian winter.udThe effects of TSSM feeding on hop production and the control of TSSMudon hops by various means were studied in the two consecutive seasons. Ifudunchecked, the mite can cause as much as 30% loss in cone production. Theudloss is mainly due to the reduction in numbers of cones hop plants produceudunder high mite feeding pressure. Damage was most often associated withudlarge numbers of immature TSSM. However, mite populations can beudeffectively suppressed by either multiple application of Summer-oil/ Limesulphur,udor the release of predacious mite P. persimilis at appropriate time.udA tolerance to mite feeding by hop plants was demonstrated. Ifudinsufficient numbers of cones are formed due to mite infestation, hop plants udwill produce larger cones to achieve maximum production.udTwo cultural activities can be effectively included into a TSSM controludprogramme. Ploughing hop fields in late August - early September, afterudoverwintering adults have moved onto notably thistles, can retard the buildudup of TSSM populations. Furthermore frequent use of overhead sprinklerudirrigation of hop fields can result in suppression of TSSM populations.udSeveral simple ways of assessing TSSM densities on hops were assessedudin 1987-88 and were employed throughout this study. A 'modified countingudmethod' was developed for estimating mite densities using a mite-brushingudmachine. Adult female mite densities were estimated in hop fields by theudnaked eye and these counts related to total numbers of all mite stages.udIn the phenology of the hop plant economic damage by mites was causedudthrough infestation during the flowering phase and not by infestation of theudearlier vegetation growth phase. Trial results indicated that application ofudSummer-oil during the post-vegetation phase could provide a potentialudalternative to conventional miticides.