Aspectos bioecológicos de Helicoverpa armigera (Hübner) e Spodoptera frugiperda (J.E. Smith) (Lepidoptera: Noctuidae) na cultura do grão-de-bico (Cicer arietinum L.)

Abstract

Chickpeas (Cicer arietinum L.) are one of the most important legumes cultivated in the world, and the second most consumed, especially in Asia. However, in Brazil its production has been insufficient to meet the domestic demand, being necessary to import almost all of it for consumption. To obtain a good productivity of this crop it is necessary to consider several factors, where the knowledge of the potential pest species and their management are essential. The species Helicoverpa armigera (Hübner) and Spodoptera frugiperda (J.E. Smith) belong to the Noctuidae family and attack important agricultural crops, causing damage in both vegetative and reproductive stages of crops. Therefore, we evaluated the population fluctuation of H. armigera and S. frugiperda in chickpea fields, establishing the correlation of their occurrence with some climatic factors. We also determined the biology and the fertility life table of these species on chickpeas, compared to an artificial diet. To record the population fluctuation of adults, delta-type traps were used, containing specific pheromones for these two species, in addition to the monitoring of caterpillars with the beaten cloth, performing 10 repetitions in random places. For the biology and fertility life table studies, the artificial diet and vegetative and reproductive structures of chickpea were used to feed caterpillars from the first larval instar, which were individualized in plastic containers under laboratory conditions. The biology study was composed of four treatments, being two diets (artificial diet and chickpea) and two caterpillar species (H. armigera and S. frugiperda) with 17 replicates/treatment, each replicate being composed of a group of 10 caterpillars, using an entirely randomized design. To obtain the fertility life table, the adult insects obtained from the biology study (4 treatments), were separated in couples, in PVC cages, where each couple represented one repetition, having the assay a total of 20 repetitions in each treatment, in an entirely randomized design. Regarding the population fluctuation, it was possible to observe that adults and caterpillars of H. armigera occurred almost throughout the cycle of chickpea culture with their population peaks being observed in the reproductive phase. The values of adult captures in the traps and of caterpillars with the tapping cloth showed a positive correlation with minimum and maximum temperatures, while relative humidity correlated negatively. The capture of adults of H. armigera showed a significant relationship with the sampling values of caterpillars in the crop. For S. frugiperda, the population of adults also occurred during the entire cycle of the chickpea culture, however, the number of caterpillars sampled was low, not being observed a relationship between adults and caterpillars, besides not having correlations with the climatic factors. In the biology study, it was observed that chickpea provided a longer larval and pupal period for H. armigera and S. frugiperda, as well as a lower viability of larvae and pupae when compared to the artificial diet. In the fertility life table study, both species showed lower values of net reproductive rate, intrinsic growth rate and finite increase ratio on the chickpea diet compared to the artificial diet. The results obtained provide subsidies for the knowledge of population fluctuation and the biology of these pests in the crop. Despite longer larval and pupal periods, as well as lower pupal viability when the species were fed with chickpeas, both species completed their biological cycle and reproduced, indicating that they are pests of this crop.