Ecologia comportamental e de interações com plantas hospedeiras em Phyllophaga cuyabana (Moser) (Coleoptera:Melolonthidae, Melolonthinae) e implicações para o seu manejo em cultura de soja

AUTOR(ES)
DATA DE PUBLICAÇÃO

1997

RESUMO

Soybean (Glycine max (L.) Merrill) is an introduced crop which has been expanding in Brazil during the last four decades. There are still some nutricional niches unoccupied or inefficiently explored by arthropods and other colonizing herbivores. Some insects with subterranean habitat have been considered soybean pests in Brazil in the last ten years, probably due to changes in the cultivation system and crop expansion to new areas. Phyllophaga cuyabana (Moser), a native Brazilian species, has been characterized as a soybean pest in the Central Westem region of Paraná State, where the larvae attacks soybean roots. This study was carried out to increase knowledge on the biology and ecology of P. cuyabana, considering aspects such as behavior, seasonal distribution of development stages and host-plant interactions, aiming to supply information to set up a control strategy for this insect in soybean fields. The effects of various soil management and soybean cropping systems on the populations of immature and adult insects were compared. The life cycle of the P. cuyabana is synchronized with the soybean crop and its sowing in the region. The population variation pattern during the year is partly explained by physical factors, mainly temperature. The only stage which occurs above the ground is the adult. It seems to be the most susceptible and adequate for control purposes because its behavior can be used in a management strategy. During the mating season (November/December) these insects tend to gather above the soil in places where the vegetation is higher and the majority leave the soil, on alternate days, returning after copulation. The search for egg laying sites probably takes place before mate, since the adults do not fly but bury themselves in nearby places after finishing copulation. Only the females feed, and some vegetable species, such as sunflower (Helianthus annus) and Crotalaria juncea, are more consumed than soybean. The females select the copulation and egg laying sites depending on the conspicuousness of the host plant. The choice of taller plants as the copulation site seems to be related to the ease of meeting partners and the proximity of good egg laying sites. Conspicuous sites in the cultivation area, where there were large adult gatherings, are associated with a greater larvae density occurrence in the following generation in the next season. As the adults are attracted by conspicuous sites, the maize crop (Zea mays) could be used to concentrate the adults in certain areas and facilitate their control. Maize is sown well before soybean in the region and will provide an adequa te mating place. Survival of the larvae was greatly influenced by the vegetable species ingested, mainly in the early stages. The final biomass of the surviving larvae, until diapause, was smaller for larvae fed on cotton (Gossipium hirsutum), Crotalaria spectabilis and C. juncea. However, Crotalaria species, which could attract P. cuyabana adults have a high potential for integrating a management program as a trap crop. Although P. cuyabana has shown preference flexibility and has not always completely avoided unsuitable plants for the immature stages development it followed, generally, the hypothesis that the female phytophagous insects tend to lay eggs where the survival of the offspring is greatest. Conventional soil management, used in this region, generally a superficial plowing followed by disking twice, did not affect the the population. Although the populational density was similar under conventional and no tillage management, the larvae distribution observed in soil profiles suggests that the use of implements which reach a greater depth, bringing the larvae to the surface, may contribute to control the insect in areas where the occurence of high population was confirmed. Changing the soil preparation period, to after the soybean harvest in highly infested areas, could also be part of a control strategy, because in this period, the larvae are not yet very deep in the soil. The behavior and the biological aspects of the insect indicate that isolated measures would not be enough to control it. Research efforts to control the adult should continue, as this stage is more exposed to the effects of habitat variation and may be the most adequate for the use of potential biological control agents

ASSUNTO(S)

artropode inseto - comportamento soja ecologia relação inseto-planta

ACESSO AO ARTIGO

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