Comunidades de Coleoptera em cultivos de tabaco (Nicotiana tabacum L.) em Santa Cruz do Sul, RS

Abstract

The tobacco (Nicotiana tabacum L.) is a crop of major importance to Rio Grande do Sul and Brazil, but there are few studies on biodiversity associated with cultivation. Therefore, the aim of this study was to survey the families of Coleoptera associated with organic cultivation of tobacco, analyzing richness and abundance, as well as the temporal and spatial distribution of these insects. Furthermore, it also aims to perform a comparative analysis between organic and conventional cultivation of tobacco. The study was conducted on a crop with organic management in harvest 2009/2010 and 2010/2011, in Santa Cruz do Sul, RS. In the 2009/2010 harvest was also assessed a crop managed conventionally, for comparative analysis. In organic cultivation, three sampling lines were defined in order "inside-out" of crop, corresponding to: (1) line whose edge shows the adjacent vegetation abundant, mainly composed of trees and shrubs of medium and large; (2) line whose adjacent vegetation consisted of native shrub and tree species with size smaller; and (3) line with the adjacent vegetation composed of forage plants. On the other hand, in conventional cultivation, a line sample single was delimited, towards out within the crop, for comparison purposes with the line "2" of organic crop. In each line were determined three sampling points ("outside, border and inside"); and a single point within the sampling, called "middle" point. At sampling points were installed four pit-fall traps and one Malaise. In organic cultivation, the samplings were conducted, weekly, from November 20th, 2009 to March 19th, 2010 and from November 3th, 2010 to January 21th, 2011. In conventional cultivation, was from November 23th, to December 28th, 2009. In organic cultivation, were collected 49.269 coleopterans, distributed into two suborders, 13 superfamilies and 32 families. Six families accounted for about 90% of the total collected, namely: Staphylinidae (37.28%), Chrysomelidae (33.40%), Nitidulidae (7.50%), Curculionidae (5.25%), Carabidae (3.10%) and Elateridae (3.09%). The temporal distribution of Coleopterans is related, primarily, to the cycle of culture, and a reduction in the number of insects collected occurs due the subsequent harvests of tobacco leaves. On points "inside" and "middle" and on sampling lines "1" and "2", the community of coleopterans was numerically larger. The chrysomelids, being phytophagous insects, were distributed in places where there was greater food availability. However, the landscape composition of vegetation adjacent to cultivation was instrumental in the spatial distribution of predator insects belonging to Staphylinidae, considering that the highest abundance was observed in areas with greater plant diversity. The management adopted in conventional cultivation had an impact on the community of Coleoptera, especially when considering the decrease in abundance of the insects of the families Chrysomelidae and Staphylinidae.