Flutuação populacional de Thlastocoris laetus (Hemiptera: Coreidae) no Amazonas

Abstract

Pineapple is vulnerable to pests, which are among the factors that can interfere with fruit production. Among these, Thlastocoris laetus (Hemiptera: Coreidae) can be highlighted. This stink bug attacks the fruit and the stalk of infructescence, which can lead to death on the plants. Studies related to bioecology and biological control are still scarce. The present study aimed to evaluate the population fluctuation of Thlastocoris laetus (Mayr, 1866) and the main factors influencing this population fluctuation, as well as the occurrence of natural parasitism in eggs of this pest, and to verify the spatial distribution of bedbugs in the field. The study was carried out from January to December 2020. The area established was the Experimental Farm of the Federal University of Amazonas. In an orchard of 540 m2cultivated with pineapple of the cultivar “Turiaçu”. To obtain data, records and removal of adult stink bugs and their immature forms (eggs and nymphs) were performed, with evaluations being carried out on the following plant structures: chicks, fruits, crowns, peduncle and leaves. The stink bug specimens were collected in the morning, every fifteen days on twenty randomly selected plants. The pineapple bug population was associated with pineapple phenology and climatic factors in each collection period. Field egg parasitism was evaluated on the same plants in the analyses. Parasitism was calculated by the relationship between the number of parasitized eggs and the total number of eggs counted in the laying. The structures of the pineapple plant containing egg masses were also collected. Parasitism rates were estimated considering the total number of eggs collected and the number of emerged parasitoids. In order to identify the patterns of spatial distribution of T. laetus, samples obtained from the fluctuation population of collected stink bugs were evaluated. The mathematical models used to assess the spatial distribution were determined by the dispersion indices and frequency distributions. The population fluctuation of T. laetusshowed two population peaks for adults, occurring in February and March, and three for nymphs, occurring in February, May and July. Rainfall did not significantly affect the population of T. laetus, with the largest populations occurring between January and July, related to the presence of fruits in the area. Three species of egg parasitoids were identified in the research, which together presented a parasitism rate of 46.15%, considered efficient in natural parasitism. The negative binomial was satisfactory, demonstrating that the population of nymphs and adults of T. laetus has an aggregated distribution in the pineapple crop.