Spider Mite (Acari: Tetranychidae) Infestation Rate and Initiation: Effect on Cotton Yield

Abstract

A 2-yr study was conducted to investigate the effect of spider mites, Tetranychw spp., on cotton (Cossyytum hfrsutum L.) in the West Central San Joaquin Valley of California. Results of each year were analyzed by spline (i,e,, segmented) regression. In 1982, following infestation of cotton at a550 degree-days (DD) > 12°C after planting, significant reduction in yield did not occur until a critical infestation rate (change in the proportion of infested leaves) reached 0.121/100 DD, after which, yields were dramatically reduced. Results of spline regression analysis suggest that cotton is initially tolerant of spider mites, but once the infestation rate exceeds the critical rate, tolerance breaks down rapidly. This critical rate is fundamental to the economic threshold for spider mites on cotton, which is suggested to be 0.8 proportion infested, P(I), leaves. Plots treated with an acaricide at 0.8 P(I), dlid not reach the critical infestation rate and did not experience economic loss. In 1983, yield reduction was significantly greater with early infestations than with late infestations. Combining the 1982 and 1983 data into a single regression analysis showed that the txitical infesttition rate increased with later infestation initiation. In a supplemental analysis, infestation rates were weighted as a function of relative spider mite species abundance and species-specific damage. Weighted infestation rates did not significantly improve or reduce the fit of the regression function. A benefit-cost analysis indicated that once the spider mite population rate of increase exceeds the critical infestation rate, yield suppression is dramatic and sufficient to warrant management intervention. KEY 'WORDS Arachnida, Goss ypium, infestation rates, spider mites SPIDER MITES, Tetranychus spp., can be a severe economic problem on cotton (Gossypium hirsutum JOURNAL OF ECONOMIC ENTOMOLOGY Vol. 84, no. 2 greatest amount of damage, T. pacificus a moderate amount, and T. urticae the least. Because

Physiological Responses of Cotton to Two‐Spotted Spider Mite Damage

“…Tetranychus urticae feeds on the undersides of leaves, which are the major sites of photosynthesis (Tomczyk and Kropczynska, 1985; Welter, 1989). At the crop level, earlier studies have shown that T urticae infestations can have dramatic effects on plant growth, significantly reducing radiation use efficiency (RUE) and resulting in reduced crop yield, fiber quality, germination success, and oil content of seeds (Wilson et al, 1991; Wilson, 1993; Sadras and Wilson, 1996; Sadras and Wilson, 1997a, 1997b). Greatest effects on development and yield were caused by rapidly increasing mite infestations early in the growing period.…”

Interactions Between the Augmentatively Released Predaceous MiteGalendromus occidentalis(Acari: Phytoseiidae) and Naturally Occurring Generalist Predators

“…One of the best supported explanations for this observation is that insecticides decimate naturally occurring generalist predators, yet cause little mortality to spider mites (Gonzalez et al 1982, Trichilo and Leigh 1986, Wilson et al 1991a, Sclar et al 1998. When spider mite populations are no longer limited by predation they can expand and cause severe foliar damage to cotton plants (Wilson et al 1991b). Another potential reason for secondary outbreaks of mites is that broad spectrum insecticides may cause spider mite population growth rates to increase either directly or indirectly by modifying plant quality (Leigh and Wynholds 1980).…”

Population Fluctuations of Certain Mites Associated With Soybean and Cotton Plants in Relation to Climatic Factors and Leaf Phytochemical Contents

“…occupy an important position among field crops in Egypt, while cotton has traditionally been P the most important fiber crop in Egypt and the leading agricultural export crop and soybean which used for human consumption and oil extraction. Cotton and soybean are heavily infested by the phytophagous mite, Tetranychus urticae, Koch which considered one of the most important mites infesting many crops in the world and frequently causes a considerable loss in yield and fiber quality (Wilson et al, 1993, El-Khouly et al, 1998and Taha et al, 2001).…”