EFFECTS OF OZONE ON REPRODUCTION OF 2-SPOTTED SPIDER-MITE (ACARI, TETRANYCHIDAE) ON WHITE CLOVER

Twospotted spider mite, Tetranychus urticae Koch, is a significant pes t of peanut, Arachis hypogeae L., that continues to present problems a s an induced pest despite recent widespread implementation of IPM prac tices. Effects of ozone (O-3) on reproduction of twospotted spider mit es feeding on an O-3-sensitive clone and an O-3-resistant clone of whi te clover, Trifolium repens L., were investigated in a greenhouse in c ontinuous-stirred tank reactor chambers. Mite eggs of narrow age distr ibution (approximate to 6 h) were placed on white clover plants expose d to 5 treatment levels of O-3. Constant amounts of O-3 were added to charcoal-filtered air for 6 h per day to achieve 5 mean concentrations ranging from 10 to 112 nl per liter. Plants were exposed to O-3 appro ximate to 9 d before infestation with mites; daily exposures continued for approximate to 20 d after mite infestation. The developmental sta ge of each mite was recorded at approximate to 2-d intervals until fem ales were sexually mature (approximate to 10 d) and began ovipositing. Thereafter, the cumulative number of eggs produced per mite was recor ded. After approximate to 5 d Of oviposition, each adult mite was remo ved and the percentage hatch of eggs remaining on each plant was measu red for an additional 5 d. Ozone caused more chlorosis and necrosis on the O-3-sensitive clover clone than on the O-3-resistant clover clone . Increasing O-3 levels caused a significant linear decrease in develo pmental period of the mites. Estimates of time to 1st oviposition decr eased linearly with increasing O-3. Estimates of time of 1st hatch of 2nd-generation eggs decreased linearly with increasing O-3. Elevated O -3 levels appear to decrease the time required for female mites to dev elop from egg to ovipositing adult, which may have a profound effect o n the intrinsic rate of population increase. Different responses by mi tes feeding on resistant plants versus susceptible plants suggests tha t this is a plant-mediated response.