Pest species diversity enhances control of spider mites and whiteflies by a generalist phytoseiid predator

To test the hypothesis that pest species diversity enhances biological pest control with generalist predators, we studied the dynamics of three major pest species on greenhouse cucumber: Western flower thrips, Frankliniella occidentalis (Pergande), greenhouse whitefly, Trialeurodes vaporariorum (Westwood), and two-spotted spider mites, Tetranychus urticae Koch in combination with the predator species Amblyseius swirskii Athias-Henriot. When spider mites infested plants prior to predator release, predatory mites were not capable of controlling spider mite populations in the absence of other pest species. A laboratory experiment showed that predators were hindered by the webbing of spider mites. In a greenhouse experiment, spider mite leaf damage was lower in the presence of thrips and predators than in the presence of whiteflies and predators, but damage was lowest in the presence of thrips, whiteflies and predators. Whitefly control was also improved in the presence of thrips. The lower levels of spider mite leaf damage probably resulted from (1) a strong numerical response of the predator (up to 50 times higher densities) when a second and third pest species were present in addition to spider mites, and (2) from A. swirskii attacking mobile spider mite stages outside or near the edges of the spider mite webbing. Interactions of spider mites with thrips and whiteflies might also result in suppression of spider mites. However, when predators were released prior to spider mite infestations in the absence of other pest species, but with pollen as food for the predators, we found increased suppression of spider mites with increased numbers of predators released, confirming the role of predators in spider mite control. Thus, our study provides evidence that diversity of pest species can enhance biological control through increased predator densitie

Impact of Early Infestation of Two-Spotted Spider Mites (Tetranychus urticae) on Cotton Growth and Yield

Two-spotted spider mites (Tetranychus urticae Koch, 1836) are pests of vegetables, ornamentals, and row crops around the world. Two-spotted spider mites have become an important long-season pests of cotton, causing injury to cotton from an early vegetative stage. In the past eight years, Arkansas cotton acreage treated for spider mites has more than doubled and most of the increase has been attributed to early season infestations. Yield losses of up to 30% have been observed in other studies where spider mite infestation started at third true leaf. Because of the apparent change in this pest\u27s population dynamics, particularly at early stages of crop development, the objective of the present study was to understand the impact of two spotted spider mites on cotton growth and yield. This project focuses on the impact of the timing and duration of infestations. Cotton plots were artificially infested at fourth, sixth true leaf in 2012, and at cotyledon and fourth true leaf during 2013. Both years included three infestation durations (short, medium, and long) at each infestation time. Two-spotted spider mites remaining on cotton at damaging densities for two weeks or more regardless of infestation time, caused significant yield loss. However, spider mites did not cause significant yield loss when environmental conditions did not favor spider mite development for extended periods

Adaptation Mechanisms of Two-Spotted Spider Mite, Tetranychus Urticae, to Arabidopsis Indole Glucosinolates

The two-spotted spider mite Tetranychus urticae Koch is a key agricultural pest that causes significant yield losses in a wide range of economically important crops. Rapid development of resistance to several classes of pesticides in T. urticae necessitates introduction of alternative management strategies to control this pest. Indole glucosinolates (IGs) are secondary metabolites found in Brassicaceae plants (including Arabidopsis thaliana) that have been shown to be effective against T. urticae and could be potential candidates to control spider mites. However, a laboratory population selected on IG-containing Arabidopsis was able to evolve adaptation to this plant. The overall objective of this thesis was to identify the mechanism of adaptation of two-spotted spider mites to Arabidopsis and IGs. Similar expression of marker genes and levels of plant defense-related metabolites after feeding of IG-adapted and non-adapted adult spider mites indicated that plant suppression is not the strategy used by spider mites to adapt to Arabidopsis and IGs. On the other hand, higher activity of P450 monooxygenases in IG-adapted mites and the negative effect of inhibitors of these detoxification enzymes on fecundity of adapted spider mites suggested that spider mites use detoxification to overcome the effect of IGs. HPLC-mediated detection of conjugates of IG breakdown products in adapted compared to non-adapted mites supports the involvement of detoxification in the adaptation of T. urticae to IGs. In addition, RNA-seq analysis showed induction of detoxification enzyme genes upon mite feeding on IGs. Upregulation of genes associated with growth, development and fecundity in adapted spider mites suggests that T. urticae neutralizes the negative effect of IGs. Genes that were differentially upregulated in adapted compared to non-adapted spider mites likely capture gene sets associated with the adaptation to IGs, suggesting that these genes can be further used in manipulation of T. urticae to avoid development of adaptation or to succumb it

Reproduction and longevity of the predatory mite, Phytoseiulus persimilis (Acari: Phytoseiidae) and its prey, Tetranychus urticae (Acari: Tetranychidae) on different host plants

The biological control of twos potted spider mites by the predator Phytoseiulus persimilis is usually unsuccessful on greenhouse tomato crops in British Columbia. Experiments were conducted to determine the influence of host plant on the longevity and reproduction of the predator, and on the suitability of twospotted spider mites as prey. Lifespan and reproduction of P. persimilis were lower on tomato leaves than on bean leaves but feeding on spider mites that had been reared on tomato or bean leaves had no effect on the reproduction or lifespan of P. persimilis. A strain of twospotted spider mites that came from an outbreak on a greenhouse tomato crop lived for shorter periods and laid fewer eggs when confined on tomato leaves than on bean leaves. A strain of twospotted spider mites that had been maintained on bean leaves was unable to reproduce on tomato leaves. Exudates from glandular hairs were toxic to P. persimilis. Glandular hairs are important in pest management on tomato crops. Their removal through breeding might make plants more susceptible to herbivores. Therefore it would be preferable to develop other methods for biological control of twospotted spider mites on tomato

EC70-1593 Entomology : Red Spider Mite Control

Extension Circular 70-1593: Entomology-Red spider mite control; description of red spider mites, plants group that commonly damage by red spider mite. Some typical types of injuries caused by red spider mites. Red spider mite life history, and direction for red spider mite control

Avoidance of ant chemical traces by spider mites and its interpretation

害虫がアリの足跡を避けることを発見 --厄介な害虫を天然物質で追い払える可能性を開拓--. 京都大学プレスリリース. 2022-10-31.Spider mites become easy prey for ants when they leave their protective webs; therefore, the ability to avoid traces of ongoing ant activity should confer a selective advantage to mites. We examined avoidance of ant traces by the spider mites Tetranychus kanzawai and Tetranychus urticae. Both mite species avoided host plant leaves with active traces of Pristomyrmex punctatus or Formica japonica ants. Pristomyrmex punctatus trace avoidance by T. kanzawai lasted for more than 1 h, but not more than 3 h. Tetranychus kanzawai also avoided P. punctatus traces on plant stems, along which the mites access leaves. Moreover, T. kanzawai avoided hexane extracts of P. punctatus or F. japonica applied to a filter paper pathway. This study represents the first demonstration of a repellent effect of ant chemical traces on spider mites. Considering the substantial abundance and global distribution of ants in nature, such repellent effects may help to answer the long-standing question of why only a small fraction of available plant resources is used by herbivores. Although spider mites have developed resistance against many synthetic pesticides, natural compounds that simulate ant chemical traces may repel spider mites from agricultural crops

Spider mite web mediates anti-predator behaviour

Herbivores suffer significant mortality from predation and are therefore subject to natural selection on traits promoting predator avoidance and resistance. They can employ an array of strategies to reduce predation, for example through changes in behaviour, morphology and life history. So far, the anti-predator response studied most intensively in spider mites has been the avoidance of patches with high predation risk. Less attention has been given to the dense web produced by spider mites, which is a complex structure of silken threads that is thought to hinder predators. Here, we investigate the effects of the web produced by the red spider mite, Tetranychus evansi Baker & Pritchard, on its interactions with the predatory mite, Phytoseiulus longipes Evans. We tested whether female spider mites recognize predator cues and whether these can induce the spider mites to produce denser web. We found that the prey did not produce denser web in response to such cues, but laid more eggs suspended in the web, away from the leaf surface. These suspended eggs suffered less from predation by P. longipes than eggs that were laid on the leaf surface under the web. Thus, by altering their oviposition behaviour in response to predator cues, females of T. evansi protect their offspring

The presence of webbing affects the oviposition rate of two-spotted spider mites, Tetranychus urticae (Acari: Tetranychidae)

Several species of tetranychid mites including Tetranychus urticae Koch (Acari: Tetranychidae) construct complicated three-dimensional webs on plant leaves. These webs provide protection against biotic and abiotic stress. As producing web is likely to entail a cost, mites that arrive on a leaf with web are expected to refrain from producing it, because they will gain the benefit of protection from the existing web. Mites that produce less web may then allocate resources that are not spent on web construction to other fitness-enhancing activities, such as laying eggs. To test this, the oviposition rate of T. urticae adult females was examined on leaves with web. As a control, we used leaves where the web had been removed, hence both types of leaves had been exposed to conspecifics previously and were thus damaged. On leaves with web, the oviposition rate of T. urticae females was higher than on leaves where the web had been removed. Therefore, the presence of web constructed by conspecifics enhanced the oviposition rate of T. urticae females. This provides indirect evidence that mites use the web constructed by conspecifics and thereby save resources that can be allocated to other traits that enhance reproductive succes