Interactions between white mealybugs and red spider mites sequentially colonizing coffee plants

Plants under herbivore attack often respond defensively by mounting chemical and physical defences. However, some herbivores can manipulate plant defences to their own benefit by suppressing the expression of induced defences. These herbivore-induced changes specific to the attacking herbivore can either facilitate or impede the colonization and establishment of a second herbivore. Although recent studies have focused on the effect of multiple herbivory on plant induced response and the third trophic level, few have examined the ecological relevance of multiple herbivores sharing the host. Here, we investigated whether herbivory by the white mealybug Planococcus minor (Maskell) (Hemiptera: Pseudococcidae) or the red spider mite Olygonychus ilicis (McGregor) (Acari: Tetranychidae), two herbivores that peak in coffee plantations during the dry season, may facilitate the colonization and establishment of the other species in coffee plants. Dual-choice arena tests showed that white mealybugs preferred mite-infested over uninfested coffee plants as hosts. Fifteen days after the release of 50 first-instar P. minor nymphs, greater numbers of nymphs and adults were found on mite-infested than uninfested plants, indicating superior performance on mite-infested plants. On the other hand, female red spider mites did not show clear preference between uninfested and mealybug-infested plants and deposited similar numbers of eggs on both treatments. In a no-choice test, red spider mites performed poorly on mealybug-infested plants with a smaller number of eggs, nymphs, females and males found in mealybug-infested plants relative to uninfested plants. Thus, our results indicate that coffee plants are more likely to be infested by the red spider mite before white mealybug, rather than the inverse sequence (i.e. mealybug infestation followed by red spider mites). Our findings are discussed in the context of plant manipulation reported for pseudococcid mealybugs and spider mites.