Diversidade de vespas sociais em cultivo de cana-de-açúcar

Abstract

Brazil is nowadays the world's first sugar cane producer, being the state of Minas Gerais the second biggest in the southwest region. The predatory behavior of social wasps is intrinsically connected to the larval phase of insects of the Lepidotera order, many of them being pests in agricultural systems. This research’s objective is the know the variety of social wasps in the growing of sugar cane, identifying species that are cable to nest in such places. Also to analyze its tendency to change in diversity and number, regarding the sugar cane's growing phases and the weather variations (temperature (°C), relative humidity (%) and precipitation (mm)).The methods of sampling efficiency was also evaluated. The samplings took place between July 2010 and June 2011, using two different methods [attractant snares (passion-fruit juice, water and sugar and sardine broth) and active search]. Within the study 1091 social wasp were collected, ranging between seven genres and 20 species, Agelaia vicina being the most common. By its efficiency index, the active search was the most effectual method attracting 90% of the species, followed by the passion-fruit juice (35%), sardine broth (20%) and water and sugar (5%). Stability was observed on the cumulative species curve starting in the eighth month of sampling and a asymptote tendency on the variance curve made by the Jackknife diversity estimator, indicating satisfactory sampling effort. The Biggest species richness was found during hot/humid months (October/2010 to April 2011), with maximum being in October 2010 (12 species). Relation between the observed climatic variables was not found (temperature (°C), relative humidity (%) and precipitation (mm) and species richness (r=0,2379; p=0,4566), (r=-0,5208; p=0,0825) e (r=0,0860; p=0,7905) so as, between climatic variables and abundance of wasps, (rs=-0,3713; p=0,2347), (rs=-0,4476; p=0,1445) and (rs=-0,3916; p=0,2080), but there was a discernible negative co-relation between the number of wasps and the sugar cane's height (r= -0,4360; p= 0,05).In the end of the research, between the species in which nests were found around the growing area, Mischocyttarus drewseni e Polistes simillimus, were qualified as constant. It was also observed the constant presence of social wasps throughout the whole research period, having maximum number of abundance and diversity in the months of sprouting and development of the sugarcane crop growing. From the sampled species, at least nine are known as pest insects’ predators in agricultural systems, five of them having as part of its source of nourishment, caterpillars of herbivore insects in sugar cane growing areas, 25 suggesting that social wasps have potential to be utilized as natural enemies of pest insects in crops of similar characteristics.