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  • Author or Editor: Stephen R. Keith x
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In this study, we report on the compatibility of two commercially available predatory mites, Neoseiulus californicus and Phytoseiulus persimilis, with three miticides used in greenhouse production systems to control the twospotted spider mite, Tetranychus urticae. We determined the lethal effects of the miticides chlorfenapyr, spiromesifen, and bifenazate to both predatory mite species 24 hours after exposure to spray applications in petri dishes. Two rates of chlorfenapyr (0.40 and 0.81 mL/2-L) and spiromesifen (0.15 and 0.31 mL·L–1), and one rate of bifenazate (0.62 mL·L–1) were used. All rates were based on the manufacturer label recommendations for twospotted spider mite. Both rates of chlorfenapyr and spiromesifen, and the single rate of bifenazate were not harmful to N. californicus with percent live mite values ≥85% for chlorfenapyr and ≥95% for spiromesifen, and 93% for bifenazate. However, these same miticides were substantially toxic to P. persimilis with percent live mite values of ≤63% for all the miticides tested. Based on the results of this study, the miticides chlorfenapyr, spiromesifen, and bifenazate are compatible with N. californicus whereas these miticides are toxic to P. persimilis indicating a difference in susceptibility based on predatory mite species.

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Insect growth regulators, which are primarily used to kill the larval stages of certain insect groups, have indirect effects on the adult stage of whiteflies. In this study, we assessed the effect of the insect growth regulator novaluron (Pedestal) on the reproduction of silverleaf whitefly (Bemisia argentifolii). Two experiments were conducted by exposing adult female silverleaf whiteflies to the low [0.47 mL·L-1 (6 floz/100 gal)] and high [0.63 mL·L-1 (8 floz/100 gal)] label-recommended rates of novaluron. There was also an untreated control. Infested plants [mist flower (Eupatorium coelenstinum) and transvaal daisy (Gerbera jamesonii) for Expt. 1 and Expt. 2, respectively] containing adult female silverleaf whiteflies were sprayed with novaluron using a carbon dioxide (CO2) backpack sprayer. Plants were immediately placed into cages covered with antivirus insect screening. After 24 hours, six adult female silverleaf whiteflies were aspirated from the treated plants, and immobilized with CO2 before being placed onto untreated plants [transvaal daisy for Expt. 1, and rose-of-china (Hibiscus rosa-sinensis) for Expt. 2]. Three munger cells containing two adult female silverleaf whiteflies per cell were attached to leaves of each of the untreated plants. The number of live and dead eggs, and live nymphs per plant was assessed 4 and 8 days after treatment (DAT). In Expt. 1, the low rate of novaluron significantly reduced egg viability compared to the untreated control based on live nymphal counts 8 DAT. In Expt. 2, both rates of novaluron significantly reduced egg viability compared to the untreated control, based on live nymphal counts and number of dead eggs 8 DAT. The results from this study indicate that novaluron negatively affected female silverleaf whitefly reproduction by reducing egg viability, which may decrease the number of silverleaf whiteflies produced during a cropping cycle. This is an important long-term pest management strategy that may reduce the number of insecticide applications and decrease labor costs.

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Twospotted spider mite, Tetranychus urticae, is a major arthropod pest in greenhouses. Greenhouse producers typically use miticides to control twospotted spider mite (TSM) populations. This study, which involved two replicated experiments, was designed to assess the persistence or longevity and efficacy of translaminar miticides with the active ingredient (a.i.) etoxazole, chlorfenapyr, abamectin, and spiromesifen by applying these miticides to either butterfly bush (Buddleia davidii) or marigold (Tagetes erecta) plants, depending on the experiment, and then artificially infesting the plants with TSM. Based on percent mortality and number of live and dead TSM, several miticides provided adequate control of TSM even after having been applied to the test plants 14 days before being artificially infested with TSM. This suggests that these miticides have extended residual activity. The etoxazole 10 to 12 μm and etoxazole water-dispersible formulations provided control (greater than 85% mortality) of TSM over the course of Expt. 1 with four or less live TSM recovered from treated plants across the three evaluation times (21, 28, and 42 days). Spiromesifen, in Expt. 2, was significantly more effective against both the nymph (89% to 99.2%) and adult (37.3% to 87.9%) stages of the TSM than the other miticides and killed more nymphs (165 to 227) than the other treatments. In general, none of the miticides provided consistent or adequate control of TSM adults across all three evaluation times (49, 56, and 70 days).

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The twospotted spider mite, Tetranychus urticae, is a major arthropod pest of many greenhouse-grown horticultural crops. Greenhouse producers use a variety of miticides to suppress twospotted spider mite populations. A group of miticides known as mitochondria electron transport inhibitors or METIs include acequinocyl, fenpyroximate, and pyridaben. In addition, there are strobilurin-based fungicides such as azoxystrobin, kresoxim-methyl, and trifloxystrobin that are also known as METIs. We conducted a study to determine if these METI fungicides had any miticidal properties against the nymph and adult stages of the twospotted spider mite. The designated treatments were applied to marigold (Tagetes erecta) plants naturally infested with twospotted spider mites. Assessments of live and dead twospotted spider mite nymphs and adults were conducted 3, 7, and 14 days after applying the treatments. None of the METI fungicides had any activity against the nymph and adult life stages of the twospotted spider mite, with percentage mortality values <18%. The METI miticides appeared to be more effective against twospotted spider mite nymphs than the adults based on percentage mortality values across the three evaluation periods (35.2% to 100% for nymphs and 11.4% to 87.9% for adults). This study demonstrated that the strobilurin-based fungicides have negligible negative effects on twospotted spider mites.

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