Western flower thrips, Frankliniella occidentalis (Pergande) (Thysanoptera: Thripidae), is an important insect pest of greenhouse-grown horticultural crops worldwide ( Cloyd, 2009 ; Kirk, 2002 ; Lewis, 1997a ; Reitz, 2009 ; Robb and Parrella
Western flower thrips, Frankliniella occidentalis (Pergande) (Thysanoptera: Thripidae) are one of the most destructive insect pests of horticultural crops ( Helyer and Brobyn, 1992 ; Jensen, 2000 ; Kirk, 2002 ; Kirk and Terry, 2003 ). The
Western flower thrips, Frankliniella occidentalis (Pergande) (Thysanoptera: Thripidae), is an insect pest of horticultural crops worldwide ( Cloyd, 2009 ; Kirk, 2002 ; Mouden et al., 2017 ; Reitz, 2009 ; Robb and Parrella, 1995 ). Western
Western flower thrips, Frankliniella occidentalis (Pergande) (Thysanoptera: Thripidae), and fungus gnats Bradysia spp. (Diptera: Sciaridae) are major insect pests of greenhouse production systems ( Cloyd, 2008 , 2009 ; Hamlen and Mead, 1979
Chemical and physical methods were tested to determine their effectiveness in controlling Western Flower Thrips, Frankliniella occidentalis (Pergande), in greenhouses. Comparisons were made between abamectin (Avid); Spinosyn A and D, formulated from the soil Actinomycete, Saccharopolyspora spinosa (Spinosad); azadirachtin (Margosan-O); and diatomaceous earth, a physical control aimed at deterring pupation. Results based on the number of thrips counted in gerbera (Gerbera jamesonii L.) flowers indicate that the chemical treatments were significantly more effective in reducing populations than the diatomaceous earth. Over time, the population of thrips in both the Avid and Spinosad treatments was reduced to zero. Diatomaceous earth treatments reduced populations almost 50% as compared to the control, while reductions from Margosan-O ranged 50-90%.
Research focused on alternative methods to control Western flower thrips (Frankliniella occidentalis Pergande), encompassing chemicals from varying classes, parasitic nematodes, microbial insecticides, and physical/mechanical deterrents. Chemical spray applications were applied weekly for 4 to 6 weeks. Experiment 1 made comparisons between fenoxycarb (Precision), bifenthrin (Talstar), and entomopathogenic nematodes (Biosafe). Experiment 2 compared abamectin (Avid), spinosyn A and D (Spinosad), azadirachtin (neem extract: Margosan-O), and diatomaceous earth (a physical control aimed at deterring pupation). Experiment 3 compared Spinosad, fipronil, and two microbial insecticides (Naturalis-O and Mycotrol). The number of thrips counted in flowers after treatments had been applied indicated that the strict chemical treatments (Avid, Spinosad, fipronil) provided quick knockdown and overall longer-term population control. Microbial insecticides, diatomaceous earth, and nematodes maintained populations at a lower level than the control, but were not as effective as strict chemical controls. Margosan-O, Precision, and Talstar controlled populations at medium levels. For periods when populations may cycle upward, more potent chemicals could be used (Spinosad, fipronil, and Avid) while still avoiding problems associated with more toxic chemicals.
Greenhouse managers tank mix pesticides to broaden the spectrum of pest control, and reduce pesticide and labor costs. However, the effect of tank mixing an assortment of pesticides on efficacy to control pests has not been documented. This study assessed how tank mixing commercially available insecticides and miticides in two-, three-, and four-way combinations impacts the control of western flower thrips (WFT), Frankliniella occidentalis in greenhouse experiments and a laboratory bioassay. The pesticides screened were spinosad, abamectin, bifenazate, azadirachtin, and imidacloprid. Each pesticide was applied at the label-recommended rate. In the greenhouse experiments, transvaal daisy (Gerbera jamesonii) and lisianthus (Eustoma grandiflorum) flowers were inoculated with 25 adult WFT, and then flowers were sprayed with the designated treatments. After 72 hours, flowers were emasculated to assess the numbers of live and dead WFT. In the laboratory bioassay, chrysanthemum (Dendranthema grandiflora) leaf disks, treated with each pesticide and all tank mixes, were exposed to 15 adult WFT. The numbers of live and dead WFT were assessed after 48 hours. For all three experiments, no antagonistic tank mixes were identified. All treatments with spinosad, including the individual application and tank mixes, resulted in high mortality of WFT based on the numbers of live and dead WFT recovered. Our data suggest that tank mixes of spinosad with the other pesticides tested do not affect the efficacy of spinosad in controlling WFT. This information is important to greenhouse managers who want to tank mix pesticides and still control WFT in addition to the other plant-feeding arthropods found in greenhouses.
Host-plant nutritional status may affect the incidence and development of western flower thrips (WFT; Frankliniella occidentalis Pergande). Two greenhouse experiments were conducted to determine the responses of WFT population levels on impatiens (Impatiens wallerana Hook.f.) when plants were fertilized with commercially practiced rates of nitrogen (N) and phosphorus (P). Impatiens `Dazzler Violet' were grown with nutrient treatment combinations of 2 N rates (8 and 20 mm) by 2 P rates (0.32 and 1.28 mm). Individual plants grown in thrips-proof cages were inoculated with WFT at 2 or 4 weeks after transplant, in separate experiments, representing vegetative or reproductive stages of plant growth, respectively. Plants were destructively sampled weekly for 4 weeks following inoculation. Plant tissue N and P concentrations were significantly different across treatments: 8 and 20 mm N resulted in 4.9% and 6.3% N in tissue, respectively; 0.32 and 1.28 mm P resulted in 0.37% and 0.77% P in tissue, respectively. Nitrogen rates had no effect on WFT population levels. However, 4 weeks after inoculation with adult female WFT during the vegetative growth stage, plants fertilized with 1.28 mm P had more adult WFT than those fertilized with 0.32 mm P. Feeding damage varied depending on whether plants were inoculated in the vegetative stage with adult WFT or during reproductive growth with immature WFT. Plant size and number of flowers were lower in plants inoculated during the vegetative growth stage with adult WFT but were not affected when inoculation with immature WFT occurred during the reproductive stage, as most WFT were found feeding inside the nectariferous spurs of the flowers. Tissue N was lower in WFT-inoculated plants compared to noninoculated plants in both experiments.
Experiments were conducted to investigate the feasibility of biological control measures to control Western Flower Thrips. Thrips population and preferred trap color were examined using sticky trap tapes in 5 fluorescent colors, orange, yellow, green, blue and pink. Results indicated that pink is more effective in attracting thrips than the traditional yellow or the newly acclaimed blue sticky traps on the market now. Studies were also conducted to determine if the entomogenous nematode (Steinernema feltiae) could invade and parasitize Western Flower Thrips, and which stage of the thrips life cycle was most susceptible to parasitization. Thrips were dissected and checked for nematode invasion at 24, 48 and 72 hours after inoculation. S. feltiae was found to invade the body cavity after 24 hours in the larval stage of Western Flower Thrips resulting in death.
Western flower thrips are an ever-increasing problem in greenhouse floriculture crops. Thrips resistance to pesticides as well as tighter regulations on pesticide use are making thrips management in the greenhouse more difficult. To improve host plant resistance, a study was conducted to determine if impatiens cultivars varied in their susceptibility to western flower thrips feeding damage. In a replicated study, nine impatiens cultivars were inoculated with about 30 thrips. Thrips were allowed to feed on individual plants during an 8-week period of growth. During plant growth, visual evaluations to estimate thrips feeding damage were conducted every 2 weeks. At the conclusion of the experiment, a final visual evaluation was made and thrips numbers were determined. Cultivars varied in estimates of thrips feeding damage. Several cultivars exhibited significantly reduced levels of thrips feeding damage. Of these cultivars, some had high thrips population levels, indicating tolerance, while other cultivars had low thrips population levels, an indication of antibiosis. One cultivar was determined to be highly susceptible to thrips feeding damage. This cultivar was so damaged by the end of the study, remaining plant material was unable to support thrips populations. Variability was found in the levels of thrips feeding damage and thrips population levels indicating the presence of tolerance and/or antibiosis. Because of detected variability, the potential for improving impatiens resistance to thrips feeding damages exists.