Efeito de diferentes épocas do plantio de feijão-caupi (Vigna unguiculata (L.) Walp.) na dinâmica populacional de insetos-praga e seus inimigos naturais

Abstract

The present work aimed to evaluate the effect of different planting times on the population dynamics of insect pests and their natural enemies of the cowpea culture. The study was carried out at three times of the year, from september/2017 to august/2018 at the Experimental Farm of the Federal University of Amazonas FAEXP. Weekly samplings were performed, totaling 33 collections. Two forms of collection were used for each planting season: individual evaluation of the plants per linear meter at 10 random collection points and entomological network (10 networks at 10 collection points) according to the phenological stage of the culture. Through the fauna analysis, carried out in the three planting seasons, it was possible to verify that Acromyrmex sp.; Agromyzidae sp. Cerotoma arcuata, Crinocerus sanctus, Euschistus heros, Horciasinus signoreti and Nezara viridula were species considered to be pests of the cowpea culture, with emphasis on H.signoreti as it was the first time considered predominant in cowpea plantations in the state of Amazonas. The natural enemies observed in the analyzed times are from the groups of parasitoids and predators. Among the parasitoids, the most abundant family was Tachinidae (Diptera) and of the predators, Dolichopodidae (Diptera), Syrphidae (Diptera) and Formicidae (Hymenoptera). However, it was possible to verify that there was no significant difference for the total of pest insects collected between the studied periods. However, advancing or delaying the planting season there will always be infestation of the hemiptera: C. sanctus, N. viridula, E. heros and H. signoreti, although, apparently, the species of bedbugs reported as of economic importance, in this work, showed preferences for specific seasons with the exception of H. signoreti, which occurred and were dominant in the three seasons. The largest population peaks of hemiptera occurred in the reproductive stages. The change in the planting season provided a smaller population of the defoliating insect of greater economic importance for the cowpea crop, C. arcuata, in the first and second season and greater infestation at the recommended time for planting (june to august). The highest production recorded was in the second planting season, 420 kg, but with less use of dry grains due to losses caused by direct and indirect factors during planting. Therefore, if the intention is to obtain a better use of dry grains and to reduce the infestation of C. arcuata, it is suggested that the planting be carried out later, because, in this way, the damages caused by this pest tend to be in smaller proportions due to the low infestation of these insects at this time of planting.