Sobrevivência diferencial de pupas de Euselasia apisaon Dahman (Lepidoptera: Riodinidae) em plantas de sub-bosque nos plantios de Eucalyptus de Belo Oriente, MG

Abstract

-Herbivorous insects may attack eucalyptus causing economic losses. One of these pests is the moth Euselasia apisaon Dahman, a key pest in the basin of middle Rio Doce. Here we studied the survival of pupae of this moth in Eucalypts and in understorey plants and tested the hypotheses: i) live pupae are more abundant in plants of the understorey than in eucalyptus, ii) there is no difference between the abundance of pupae in different plants of the understorey. We sampled three areas cultivated with eucalyptus in Belo Oriente, MG, and samples were taken in five plots each area, getting five branches of each plant and of five eucalyptus trees that bordered the plot. The proportion of live and dead pupae and the mortality rate were estimated. The abundance of live pupae was higher in the understorey and the mortality rate of pupae was the same among different families of plants of the understorey. It is possible the larger available leaf area of understorey plants justify the greater abundance of live pupae in this habitat, however, avoidance of feeding habitat to finish the life cycle is also a possible explanation. Mortality rate in plants of the understorey points to an equal pressure of natural enemies on the pupae. These appointments help us to understand the dynamics of pests in eucalyptus plantations, providing important information to support actions against pests in natural environments. O lepidóptero apresenta cinco estádios larvais, com duração média total de 28 dias (Santos et al 1993). As suas larvas são gregárias, locomovendo-se enfileiradas ou agrupadas em semi-círculos e o seu período de pupa dura cerca de seis dias, ocorrendo no tronco de Eucalyptus ou nas plantas do sub-bosque (Santos et al 1996). Dada a grande voracidade que as lagartas de E. apisaon apresentam (Santos et al 1993), é possível que em surtos da praga as pupas localizadas longe dos sítios de alimentação tenham maior probabilidade de sobrevivência do que as pupas localizadas nos sítios de alimentação. Nessas situações, há maior risco de queda acentuada das folhas de Eucalyptus e consequente exposição das pupas a predadores.A ação de inimigos naturais é importante no controle biológico de pragas (Snyder & Ives 2003 e é possível que ela seja maior em Eucalyptus, sítio de alimentação das lagartas, do que nas plantas do sub-bosque, já que as lagartas representam um montante de recursos concentrado em Eucalyptus. De certo modo, se as lagartas puparem mais frequentemente no sub-bosque, então podese propor que esse habitat representa um refúgio para a sua população (MacArthur 1958), tornando-as menos disponíveis a seus predadores, aumentando, consequentemente, sua taxa de sobrevivência.

Survival of a Lepidopteran Defoliator ofEucalyptusis Influenced by Local Hillside and Forest Remnants in Brazil

“…Euselasia eucerus pupate on eucalyptus leaves and trunks, on other plants in the forest understory (Sousa et al 2010), and on the ground. This behavior can make predator/parasitoid encounters unpredictable during active searching, and the predation was higher at the higher resource abundance in the xeric environment, but parasitism showed no differences between environments (Fig.…”

“…It is found in Minas Gerais, São Paulo, Santa Catarina and Rio Grande do Sul states, Brazil . Euselasia eucerus increases in density, especially during the driest months of the yr, and it has multiple generations per yr in eucalyptus plantations (Sousa et al 2010).…”

Can the Understory Affect the Hymenoptera Parasitoids in a Eucalyptus Plantation?

“…The similarity in the abundance of the Hymenoptera parasitoids in the eucalyptus stands with or without an understory may reflect the fact that their populations are originated from the fragments of the native forest [ 38 ] surrounding the plantations. This can increase the biodiversity in the crop area acting as the reservoirs and biological corridors of movement and distribution of the natural enemies in the eucalyptus plantations [ 7 , 39 , 40 ]. Thus, fragments of the native vegetation between the eucalypt stands could maintain the populations of the natural enemies even when their hosts become scarce in the eucalyptus plantations, besides allowing their migration to the interior of such plantations [ 41 ].…”

“…The fusion of the conservation areas can facilitate the dispersal of the insects to the eucalyptus stands, especially those of the natural enemies [ 42 ]. A mosaic landscape composed of both cultivated and fragments of native vegetation can create multiple habitats for the breeding, feeding and sheltering of the natural enemies [ 7 , 43 ]. This can improve the environmental stability in the homogeneous stands [ 18 ], and reduce the lepidopteran defoliator populations in the forest plantations [ 44 ].…”

“…Food availability is an important factor to supply the energy for locomotion or flight and to maintain the longevity and fecundity of the natural enemies [ 5 ]. Herbs and shrubs [ 6 , 7 ], including plants such as Apiaceae, Asteraceae and Fabaceae may harbor hosts or prey [ 7 ] which can increase the diversity and abundance of the natural enemies [ 8 ]. In addition, plants, including the cultivated species have special structures as hair, domatia and nectaries that provide shelter for the natural enemies [ 5 ].…”