Potencial de ácaros predadores para o controle de Tetranychus ludeni zacher em algodoeiro

Abstract

Diverse species of arthropods can cause significant reduction in cotton harvest, and also affect other attributes such as fibre quality and seed feasibility. Among them is the red-spider-mite Tetranychus ludeni Zacher (Acari: Tetranychidae), which has been occurring in cotton plantations of the semiarid region of Pernambuco, more frequently than other secondary pests for the culture. The main method of mite control and other organisms that attack cotton plants is the use of synthetic acaricides, which has generated undesirable consequences such as the development of resistance of some species to the products, death of natural enemies, among others. Taking this problem into consideration, research is being developed aimed at integrated pest management with joint actions for the control of herbivores, in order to keep the pest population below the economic damage level. In this sense, this study evaluated the potential of predatory mites in the control of mite-pest Tetranychus ludeni in cotton crop in the semiarid region of Brazil. Chapter 1 evaluated the preference of phytophagous mite T. ludeni on cotton crop varieties with different trichomes densities. The mite presented preference for stay and oviposition in the varieties BRS 201 and BRS Safira, which have the highest densities of trichomes, among the varieties tested. Therefore, the highest densities of trichomes were preferred by T. ludeni, demonstrating that the leaf pubescence did not have any effect on the herbivore. Possible causes are being discussed in response to the relationship found between plants and herbivore. Based on T. ludeni’s preference among the cotton plant varieties, chapter 2 evaluated the functional and numerical responses of the predatory mites Euseius concordis and Neoseiulus idaeus on two phases (eggs and adults) of T. ludeni in the variety of cotton plant BRS 201. The experiments were conducted in a laboratory with adult females of each predator, individualized in arenas of cotton leaf of 10 cm (Ø). Two phases of T. ludeni as prey (eggs and adults) were offered, separately, on the following densities: 05, 15, 25 (5 repetitions) 50, 75 and 100 (3 repetitions), with replacement of dead preys at each evaluation. Every 24 hours, the number of dead prey and eggs laid by the predators was evaluated during seven days. It was observed that for both predators, the functional response was type II, with greater consumption of T. ludeni eggs than adults. When analysing the manipulation time (Th) and attack rate (a) of T. ludeni eggs and adults by the two predators, the highest attack rate occurred in eggs of this phytaphogous. Furthermore, the manipulation time of the prey was inversely proportional to the attack rate and both predators spent more time manipulating adult individuals. The numerical response of E. concordis presented higher reproductive success at densities of five to 50 T. ludeni adults, while for N. idaeus, occurred at density of 25 adults. The functional and numerical responses are associated, since both are influenced by the availability of prey and contemplate with regard to the potential evaluation of a biological pest control agent. Thus, the results found indicate that the predators E. concordis and N. idaeus have potential to control T. ludeni in different densities of cotton plant. However, it is worth pointing out that further studies are important to assess the interaction of these organisms with other control methods used in the culture, in order to optimize its use in pest management programs.