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Life history variation is a general feature of arthropod systems, but is rarely included in models of field or laboratory data. Most studies assume that local processes occur identically across individuals, ignoring any genetic or phenotypic variation in life history traits. In this study, we tested whether field populations of Pacific spider mites (Tetranychus pacificus) on grapevines (Vitis vinifera) display significant intraspecific life history variation associated with host plant cultivar. To address this question we collected individuals from sympatric vineyard populations where either Zinfandel or Chardonnay were grown. We then conducted a “common garden experiment” of mites on bean plants (Phaseolus lunatus) in the laboratory. Assay populations were sampled non-destructively with digital photography to quantify development times, survival, and reproductive rates. Two classes of models were fit to the data: standard generalized linear mixed models and a time-to-event model, common in survival analysis, that allowed for interval-censored data and hierarchical random effects. We found a significant effect of cultivar on development time in both GLMM and time-to-event analyses, a slight cultivar effect on juvenile survival, and no effect on reproductive rate. There were shorter development times and a trend towards higher juvenile survival in populations from Zinfandel vineyards compared to those from Chardonnay vineyards. Lines of the same species, originating from field populations on different host plant cultivars, expressed different development times and slightly different survival rates when reared on a common host plant in a common environment. [ABSTRACT FROM AUTHOR]

Abstract: We studied the effects of temperatures from 10 to 40°C on development of the Pacific spider mite, Tetranychus pacificus (McGregor), and the Willamette spider mite, Eotetranychus willamettei McGregor (Acari: Tetranychidae), feeding on grape foliage. In addition, we investigated the influence of temperatures from 10 to 37°C on development of the western predatory mite, Galendromus occidentalis (Nesbitt) (Acari: Phytoseiidae), feeding on T. pacificus and evaluated the suitability of E. willamettei as prey for the predatory mite at 28°C. Using a non-linear development rate model we estimated that the lower threshold for development of the three mites lay around 10°C. T. pacificus was the most heat-resistant, with its upper threshold for development at 40.3°C, followed by G. occidentalis at 37.1°C and E. willamettei at 31.0°C. T. pacificus developed significantly more rapidly than E. willamettei above 22.8°C, whereas G. occidentalis developed significantly faster than either spider mite from approximately 11 to 36°C. G. occidentalis developed 5% faster when feeding on E. willamettei than T. pacificus at 28°C. These results confirm field observations linking E. willamettei damage to cooler, coastal vineyards and early in the season in inland vineyards, and T. pacificus infestations to hot vineyards in inland and coastal areas. Although T. pacificus seems to be more heat tolerant than G. occidentalis, additional information on temperature effects on adult life history details of the two mites is needed to fully evaluate G. occidentalis performance at high temperatures. [Copyright &y& Elsevier]

We evaluated the relationships between plant water status and leaf temperature, and between leaf temperature and spider mite (Acari: Tetranychidae) and predatory mite (Acari: Phytoseiidae) populations in eight vineyards in California in 2006 and 2007. Temperature of south-facing leaves increased significantly by 0,8°C for every 1.0°C increase in ambient air temperature, and by 5.3°C for every one MPa drop in leaf water potential. Peak population densities of Pacific spider mite, Tetranychus pacificus McGregor, increased significantly with increasing frequency of leaf temperatures above 31°C. In contrast, peak population densities of Willainette spider mite, Eotetranychus willamettei (McGregor),showed no relationship with the frequency of leaf temperatures above 31°C. This differential relationship between the two mite species and high leaf temperatures is consistent with their upper thresholds for development, which are 40°C for T. pacificus and 31°C forE. willamettei, as identified in a previous study. Predatory mite population densities showed no relationship with peak population densities of either spider mite species during the analysis period, but decreased with the frequency of leaf temperatures above 31°C. In addition, predatory mite population densities were significantly higher on south-facing than interior leaves after adjusting for the effect of leaf temperature. These results help to explain why outbreaks of T. pacificus occur in warmer or water-stressed vineyards, whereas E. willamettei develops higher populations in cooler or well-irrigated vineyards. In addition, these results suggest that regulated deficit irrigation should be implemented with caution, especially in those vineyards with a high risk of T. pacificus outbreaks. [ABSTRACT FROM AUTHOR]

Abstract: The western predatory mite, Galendromus occidentalis (Nesbitt) (Acari: Phytoseiidae), is a predator of Pacific spider mite, Tetranychus pacificus McGregor (Acari: Tetranychidae), in California vineyards. We evaluated the effects of six pesticides on biological control of T. pacificus on grape plant microcosms in a two-way design: presence and absence of G. occidentalis crossed with presence and absence of pesticide. The insecticide imidacloprid did not affect T. pacificus population growth rate, but it led G. occidentalis populations close to extinction. As a result, T. pacificus populations grew significantly higher in microcosms with release of G. occidentalis and treated with imidacloprid than with G. occidentalis alone. The fungicide wettable sulfur significantly decreased T. pacificus population growth rate but it did not affect G. occidentalis. Consequently, T. pacificus populations were significantly lower in microcosms with release of G. occidentalis and treated with wettable sulfur than with G. occidentalis alone. The insecticide buprofezin had no effect on T. pacificus population growth rate. Although buprofezin did not impact the ability of G. occidentalis to suppress T. pacificus, it negatively affected G. occidentalis population growth rate. The fungicides trifloxystrobin and tebuconazole and the insecticide methoxyfenozide had no influence on T. pacificus or G. occidentalis population growth rates. Furthermore, none of the pesticides affected the sex ratio of G. occidentalis, but buprofezin, methoxyfenozide and trifloxystrobin affected its stage structure. Our study demonstrates that simultaneous testing of the demographic effects of pesticides on pests and natural enemies is essential for a full assessment of pesticide impacts on biological control. [Copyright &y& Elsevier]

Plant response to imposition of biotic and abiotic stresses by inducing their defense mechanisms, with the production of reactive oxygen species (ROS) representing a major defense response. The present work examined the simultaneous impact of two key stress factors, drought and spider mite attack ( Tetranychus urticae ) in Medicago truncatula plants. Hydrogen peroxide (H 2 O 2 ), lipid peroxidation (MDA content) and proline content in well-watered and drought-stressed leaves infested by spider mites along with neighboring leaves were examined in order to investigate the local and systemic effect of the two stresses on the antioxidant and osmoprotective response. High levels of lipid peroxidation were recorded in plants under drought stress and plants under combined drought stress and spider mite feeding compared with control plants. Hydrogen peroxide biosynthesis was significantly induced in plants under drought and spider mite attack, with highest levels detected in the feeding leaf (local response). Proline was accumulated in drought stressed-plants, with the highest levels observed in plants exposed to a combination of drought stress and mite feeding. RT-qPCR expression analysis of key genes implicated in ROS metabolism ( PAO, DAO, AOX, CuZnSOD, FeSOD, MnSOD ) and proline biosynthesis ( P5CR, P5CS ) pointed to different patterns of regulation between abiotic and biotic stress, as well as their combination. Exposure of plants to both drought stress and attack by spider mites mainly affected the local antioxidant and osmoprotective response of Medicago truncatula , highlighting the relative significance of drought-induced phenomena in combined drought/mite infestation stress responses. [ABSTRACT FROM AUTHOR]

We investigated the effect of water stress on the growth and essential oil quality of lavender ( Lavandula angustifolia ) and Greek sage ( Salvia fruticosa ) plants. In addition, we assessed the toxicity of essential oils to females of the two-spotted spider mite ( Tetranychus urticae ). Lavender and sage plants were grown in a greenhouse under adequate irrigation (AI), moderate (MWD) and severe water deficit (SWD). Plant growth related parameters, total phenols and total chlorophylls content as well as the yield and composition of essential oils hydrodistilled from the plants were assessed. In general, plants under water stress exhibited reduced growth and altered chemical composition than plants under regular irrigation. In addition, water stressed plants benefited in essential oil yield and quality, with higher concentrations of antioxidants (phenolic) level. The LC 50 of lavender essential oil vapors from control plants was estimated at 4.93 μl/l, while that of Greek sage at 3.77 μl/l. Essential oil vapors from lavender plants under MWD caused significantly higher mortality to T. urticae females, than essential oils from plants under AI. In contrast, essential oils from sage plants under water stress caused similar mortality to T. urticae irrespectively of water stress levels. [ABSTRACT FROM AUTHOR]