Biological cycle of Selenothrips rubrocinctus in roses, predatory activity and functional response of Chrysoperla externa

Abstract

The rose bush (Rosa sp.) is the most cultivated cut flower in Brazil, being one of products that have been promoting expansion of the market in recent years. Several challenges are faced in cultivation of rosebushes, most of them related to occurrence of pests, which worsen when conducted in partially or totally protected environments. Among the pest arthropods associated with rosebushes is Selenothrips rubrocinctus (Thysanoptera: Thripidae), a species recently reported for that crop and which, until then, little is known about its biology, behavior and impact of its damage to production of roses. Regarding control, studies show that chrysopids larvae (Neuroptera: Chrysopidae) can be used to manage the population of that thrips, however, little is known about the effectiveness of these predators on biological and behavioral aspects related to the interaction between the thrips and the its natural enemy. So, this study aimed to know the complete biological cycle of S. rubrocinctus in rosebushes, elaborate the life table of the species and to know the effect of this prey on the predatory activity and functional response of Chrysoperla externa. The work was carried out in Laboratório de Controle Biológico com Entomófagos (LCBE), Federal University of Lavras (UFLA), at 25±1 °C, 70±10% RH and 12h photophase. In order to study the biological cycle and prepare the life table of S. rubrocinctus rearing on rosebushes we evaluated the sexual proportion (in case of emergence of a male), duration and viability of the 1st and 2nd instar, nymph phase, pre-pupa and pupa, fecundity, duration of the pre-oviposition, oviposition, and post-oviposition periods, and its longevity, through daily observations. In order to study the effect of S. rubrocinctus on C. externa predatory activities, we used nymphs as prey for the predator’s larvae. We evaluated the predatory capacity, search and handling time and functional response. The results for the biological, reproductive and population parameters of S. rubrocinctus indicated the rosebushes as an adequate host for the development and reproduction of this thrips and evidenced the potential of this species to achieve the status of key-pest of the crop. The acceptance of thrips nymphs by C. externa larvae was demonstrated by the high number of prey consumed and high efficiency in search and handling activities. The functional response was type II, which confirms the importance of this predator in regulating thrips populations. All the instars of the chrysopid had effective predation capacity, what become this natural enemy promising in the biological control of S. rubrocinctus in rosebushes.