Western Flower Thrips Populations Research Articles

The Mirid Bug Dicyphus tamaninii as a Greenhouse Whitefly and Western Flower Thrips Predator on Cucumber

Dicyphus tamaninii Wagner is a polyphagous predator that also feeds on plants. Its effectiveness against several pests has been tested and good results have been obtained on tomato, but not on cucumber. This paper reports the results of three exclusion cage experiments. The first was carried out to evaluate the effectiveness of D. tamaninii for reducing greenhouse whitefly and western flower thrips populations on cucumber. The second experiment examined the safety of the mirid bug in terms of the potential for damaging cucumber fruits even at very low prey densities. Two predator (3 and 18 insects/plant) and variable prey release rates were used. The predator was able to reduce whitefly populations greatly, even at high initial pest infestation levels, especially at the higher release rate. Western flower thrips populations were maintained at very low densities a few weeks after the predator had been introduced into cages at the two release rates tested. The mirid bug was barely able to reproduce on cucumber in the absence of prey. Mirid feeding punctures on cucumber fruit or yield decrease due to the action of mirids were not observed. The potential of this mirid bug for inoculative and conservation biological control is discussed.

The potential of flower odours for use in population monitoring of Western flower thripsFrankliniella occidentalisPerg. (Thysanoptera: Thripidae)

Sticky blue traps are a suitable and important tool for Western Flower Thrips population monitoring in greenhouses. They can be used in vegetables and in ornamentals, and provide important information on the current status of the pest population. However, such traps cannot be used in some susceptible plant species when they are flowering because at that stage the plants are more attractive to Western Flower Thrips than the traps. We therefore tried to increase trap attractiveness by combining the colour cue with an attractive odour cue. In laboratory experiments, we found a significant additive effect on attractiveness for two odours in traps provided with both the visual and the olfactory cues as compared to traps with either cue alone. However, these results could not easily be reproduced in greenhouses. The main factors responsible for this failure seem to be (1) the only moderate, additive increase of trap attractiveness when using combined visual and olfactory cues, and (2) the problems associated wi...

Western Flower Thrips (Thysanoptera: Thripidae) Resistance to Insecticides in Coastal California Greenhouses

Field populations of western flower thrips, Frankliniella occidentalis (Pergande), showed high levels of resistance in laboratory tests to four classes of insecticides Commonly used for insect control in ornamentals. The resistance ratios (RR at LC90) to the pyrethroids permethrin and bifenthrin were very high, ranging from 138-fold (Bifenthrin, San Diego-1 [SD-1] location) to 8,716-fold (Permethrin, SD-1) Compared with a susceptible strain (UC89). Piperonyl butoxide significantly synergized permethrin up to 50-fold (SD-2), indicating that mixed-function oxidizes are a Cornponent of the overall resistance mechanism. There was moderate to high intensity of resistance to methomyl, a carbonate; RR values ranged from 41-fold (SD-1) to 378-fold (SD-2). Field resistance to chlorpyrifos, an organophosphate, was Comparatively low, with the RR values ranging from 17-fold (Santa Barbara-2 [58-2]) to 31-fold (SD-2). Although not registered for western flower thrips control, abamectin (a macro cyclic lactone) showed low to high levels of resistance (RR values ranging from 18-fold [SD-1] to 798-fold [S8-1]). The development of resistance to abamectin is the first documented case of resistance to this chemical in the field. In a separate field trial conducted at SB-1, all the chemicals tested including chlorpyrifos (microencapsulated formulation) performed poorly. Maximum adjusted control was only 53% (Pounce), confirming the field failure for all the insecticides tested at this greenhouse. Resistance to Commonly used insecticides and the likelihood of losing many more registrations emphasize the need for better and practical pest management strategies.

Relationships Among Ear Morphology, Western Flower Thrips, and Fusarium Ear Rot of Corn

The relationships among insects, corn (Zea mays) ear morphology, and ear rot caused by Fusarium moniliforme were studied in 1988 and 1989. Silks on ears of two corn hybrids, one susceptible to Fusarium ear rot and one with an intermediate level of resistance, received applications of the insecticides acephate or carbaryl at the green silk stage before the onset of ear rot symptoms. In both years, insecticide treatments reduced intra-ear populations of western flower thrips (Frankliniella occidentalis) at the brown silk stage and reduced disease incidence at maturity. In 1989, 15 corn hybrids, representing a range of susceptibility to Fusarium ear rot, were examined for ear morphology factors that may be correlated with disease incidence. Factors examined were heat units to silking; days from initial green silk to yellow-brown silk and to brown silk stages; intra-ear thrips populations at the green, yellow-brown, and brown silk stages; and husk looseness at the yellow-brown and brown silk stages. Disease incidence was correlated with thrips populations at the brown silk stage and with husk looseness at the brown silk stage but was not correlated with the other factors measured. Hybrids also could be separated by contrast analysis into susceptible, intermediate, and resistant groups on the basis of thrips populations and husk looseness at the brown silk stage. On the basis of these data, intra-ear thrips populations and husk tightness at the brown silk stage are important in the epidemiology of Fusarium ear rot

Predicting Resurgence of Western Flower Thrips (Thysanoptera: Thripidae) on Onions After Insecticide Application in the Texas High Plains

Population resurgence of western flower thrips, Frankliniella occidentalis (Pergande), was observed on onions after insecticide application during two growing seasons on the Texas High Plains. Regression models were used to quantify variables influencing western flower thrips population dynamics. Thrips densities increased exponentially after being sprayed with insecticide. This resurgence was aided by degree-days (DD) between thresholds of 5 and 35°C accumulated after insecticide application, whereas accumulated DD above a threshold of 35°C greatly hindered increase. Density of western flower thrips on onions was predicted by DD and rainfall accumulations.