Constitutive defence mechanisms among species of Capsicum pepper and their importance in managing the broad mite Polyphagotarsonemus latus (Banks, 1904) (Acari: Tarsonemidae) / Mecanismos de defesa constitutiva em espécies de pimenta Capsicum e sua importância no manejo do ácaro branco Polyphagotarsonemus latus (Banks, 1904) (Acari: Tarsonemidae)

Cláudia Helena Cysneiros Matos

Several plant species belonging to the same genus can have very different leaf, flower, and fruit traits, which often determine the occurrence, abundance, and diversity of organisms living on the plants. Leaves of Capsicum pepper plants vary considerably and range from trichome-covered to glabrous leaves. Polyphagotarsonemus latus (Acari: Tarsonemidae) is the most important pest infesting and causing severe damage in Capsicum pepper. The practice of controlling P. latus with pesticides has caused mite resistance and reoccurrence in Capsicum. Therefore, studies have been conducted to identify the most mite resistant Capsicum species. In this study we evaluate the interaction between Capsicum pepper species, the pest mite P. latus, and the predator Amblyseius herbicolus (Acari: Phytoseiidae) and tested the potential role of trichomes and domatia (as trichome tufts) on the organisms. The information is reported in four chapters, as inferences for potential use in broad mite management programs for Capsicum. In Chapter 1, the leaves of Capsicum spp. were classified according to the presence of trichomes and domatia, and their distribution and density in each species were evaluated. Significant differences were observed in the densities of domatia and trichomes in leaf veins and limbs, as well as in the total density of trichomes/cm2 and in the number of trichomes per domatia. The highest density of domatia and trichomes was found in C. praetermissum. In Chapter 2, we evaluated the development of P. latus in Capsicum species by testing the hypothesis that the broad mite population growth decreases as the density of trichomes on leaves increases. P. latus egg to adult development period varied significantly among pepper species and was longer in C. praetermissum, followed by C. annuum. The intrinsic rate of increase (rm) of P. latus varied as a function of trichome classes, where smooth leaves and leaves covered by trichomes reduced the mite rm value. In Chapter 3, we observed the population growth of P. latus in Capsicum plants, and the damage caused after inoculating 30 female mites per plant; these observations were conducted for 30 days. After the 15th day, P. latus density varied significantly among species and was higher in C. frutescens and C. baccatum. At the end of the 30-day period, mite density decreased significantly and no mites or damage were found in C. praetermissum. The P. latus instantaneous rate of increase (ri) in 15 days decreased steadily in function of the trichome classes, till the end of the experiment (30 days). However, at the end of the period, positive values were found only in plants with trichome classes 1 and 2. The species most susceptible to damage caused by P. latus were C. frutescens, C. annuum, and C. baccatum. In Chapter 4, predation of A. herbicolus on P. latus was evaluated in three pepper species with different classes of trichomes: C. baccatum, C. annuum, and C. praetermissum. Predation of one female mite in reproductive age was evaluated on 90 eggs or 90 P. latus adults. Observations were conducted every 6 hours for 24 hours, and the eggs and live adults per arena were counted. The proportion of P. latus adults predated by A. herbicolus was significantly different among pepper species. However, differences were not significant for the species C. baccatum and C. annuum, which were grouped into one treatment. At the end of the experiment, predation of P. latus eggs by A. herbicolus was significantly greater in C. baccatum and C. annuum than in C. praetermissum, a pattern also observed for this mite adult predation. The trichomes in Capsicum spp. significantly affected the tested mites and acted as a limiting factor as they were denser and better distributed on the leaf surface. To be effective, the control of P. latus in some pepper species must be conducted early, particularly among the malagueta peppers (Capsicum frutescens), the dedo-de-moça (Capsicum baccatum), and the chapéu-de-bispo (Capsicum annuum), in which P. latus population growth was very rapid and caused high damage.

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