Aspectos ecológicos, ação predatória de Phlugis teres (DE GEER, 1927) (Orthoptera - Tettigoniidae) e avaliação do seu potencial para o controle biológico de pragas em cultivares na várzea amazônica

Abstract

Phlugis teres (DE GEER, 1927) is a predacious grasshopper, representing the f amily Tettigoniidae and subfamily Listroscelinae. Aquatic macrophytes which colonize the lakes of the várzea in Central Amazonia such as Eichhornia crassipes, Paspalum repens and Echinochloa polystachya serve as a habitat for P. teres. Its life cycle depends on the arthropod fauna of these plants representing the nutritional basis. Between 08/06/90 and 19/09/91 at the várzea of Ilha de Marchantaria (lower Solimões River) the phenology and biomass of the population of P. teres was studied with respect to the oscillation of the water level.Moreover its life cycle and feeding specifity were examined as well as its potential as a predator to realize biological control of agricultura1 pests in the várzea. The population of P. teres occurs along the year indicating that it is reproducing itself continously. However, it suffers a significant reduction in its abundance during the low water period and desiccation of water bodies (mainly October and November). This period is extremly unfavourable for the host plants. In view of the unfavourable abiotic conditions, E. crassipes disappeares at the study area while P. repens and E. polystachya root in the sediment and develop adaptive forms for the terrestrial period. At that period only adults of P. teres are found. Due to their flying capacity they disperse in search for better feeding sites, since the arthropod abundance on macrophytes is also influenced by the oscillation of the river gauge, being lower during lowest water level. Oviposition of P. teres occurs endophytic on the three host plants, which allows different sites for oviposition along the year. The total number of days needed for the complete development as well as size and weight of P. teres varies with the sex. The males emerge before the females (male protandry) but the females are bigger and heavier. Both sexes have five instars e consequently pass five ecdises, the last process of transformation corresponding to the eclosion of an adult. P. teres is a voracious predator which does not have a fedding specifity, since it feeds on arthropods in particular insects of different families belonging to different orders. Therefore this grasshopper can be classified as zoophagous-polyphagous. Its predacious behaviour is caracterized by an immediate catch of the arthropod-prey using its first pair of adapted legs (with spines) to secure and imobilze the prey. ~his behaviour does not exclude individuals of the same species, which implicates cannibalism between adults (males and females) and adults over nymphs. According to trials carried out in the field and laboratory it is evident that P. teres can catch and consume agricultural pests. In the trials five species of agricultural pests were selected, which found acceptance by the predacious grasshopper . Despite the voracity and acceptibiliy of pests as nutrition, P. teres is not considered to be a predator in controlling (limiting) pests, due to its low reproduction rate. Therefore, P. teres is considered to be a predator with regulating action which can contribute to maintain the populational density of agricultura1 pests in equilibrium.