Two of the main causes of losses in tomato production are the greenhouse whitefly, Trialeurodes vaporariorum (Hemiptera: Aleyrodidae), and drought, which is becoming a central problem in agriculture due to global climate change. The separate effects of whitefly infestation and drought have been amply studied in many crop systems. However, less is known about their combined effects. To evaluate whether drought stress (DS) affects plant defense against whiteflies, we assessed the joint effects of whitefly infestation and DS on plant vegetative and reproductive performance in four tomato cultivars, and assessed the effects of DS on plant resistance and tolerance (compensatory ability) to whiteflies in a greenhouse experiment. Generally, we found negative effects of DS and whiteflies on plant performance, but the combined effects of DS and herbivory were not worse than those of either stress alone. In fact, plant performance under the combined effect of both stresses was usually similar to that in the presence of whiteflies without DS. Plants growing under DS had greater trichome density. However, plant resistance—as measured by whitefly population growth—decreased under DS in two cultivars and was unaffected in the other two. Compensatory ability decreased under DS in all but one cultivar. These cultivar-specific responses suggest genetic variation in resistance and tolerance to whiteflies and could be associated with differences in drought tolerance among cultivars. Our findings underscore the difficulty in predicting the combined effects of DS and herbivory and point to the need for a better understanding of the mechanisms underlying plant responses to both stresses at the molecular, cellular, and organismal levels.

Trialeurodes vaporariorum Westwood (Hemiptera: Aleyrodidae) is an important economic pest and has a worldwide distribution. In Chile, this species has been reported over a large geographical area and is associated with tomato production. Although several plants have been described as hosts of the whitefly, this insect’s behavior against multiple hosts is still unclear. Therefore, the objective of our work was to identify the host plants, behaviors, preferences, performance, and choices of T. vaporariorum. First, over one year, we monitored nine production sites where tomato is the principal crop and identified 50 host plants belonging to 27 families, mostly Asteraceae and Solanaceae. Among the plants, those that were most infested by greenhouse whiteflies comprised Solanum lycopersicum, Phaseolus vulgaris, Cucurbita maxima, Malva sylvestris, Bidens aurea, and Sonchus oleraceus. In laboratory tests, greenhouse whiteflies showed a greater preference for S. oleraceus, S. lycopersicum, and P. vulgaris. The highest population growth rate was observed for B. aurea, followed by S. lycopersicum and S. oleraceus. Significant differences were found in the pairwise choice test, showing a greater preference for C. maxima and S. lycopersicum. Although this pest tends to choose tomatoes, this crop was not always the first choice in terms of preference and performance. This information is necessary for the development of integrated whitefly management programs that include adjacent habitats.

Soil nitrogen (N) supplementation via fertilizers may increase crop yields substantially. However, by increasing tissue N content, added N can make plants more attractive to herbivores, effectively reducing their resistance to herbivores (ability to avoid herbivore damage). In turn, greater pest infestation may cause more severe reductions in fruit production than a moderate N scarcity. In this study, we tested whether lower N supplementation results in greater resistance to whiteflies and lower fruit production in four tomato varieties. We assessed the effects of N availability on tolerance to herbivores (degree to which fitness is affected by damage) and tested for the long-hypothesized trade-off between resistance and tolerance. Plants grown at half of an agronomically recommended amount of N had greater resistance without a significant drop in fruit production. Tomato varieties differed in resistance and tolerance to whiteflies, and showed a clear trade-off between these modes of defense. Root:shoot ratios were greater at lower N, but had no clear relation to tolerance. We estimated that the economic benefit of decreasing N addition almost fully compensates for losses due to lower tomato production. Additionally, lower fertilization rates would contribute to reduce environmental costs of large-scale use of agrochemicals.