Distribuição vertical e efeito dos inseticidas fisiológicos no controle de Euschistus heros (F.) (Hemiptera: Pentatomidae) em soja

Abstract

Soybean is one of the main crops responsible for driving Brazil's economy. However, with each season, producers have been facing serious problems due to the constant presence of pests. The brown stink bug, Euschistus heros, is currently the main species that attacks soybean crop in the Brazilian Cerrado. It begins its colonization at the end of the vegetative period or during pre-flowering, persisting until the final stage of the reproductive period, where it causes severe crop damage. For better monitoring and, consequently, effective control of the stink bug, it is important to know the insect's intraplant behavior (vertical distribution), as well as the possibility of using insecticides for its management. Therefore, this study aimed, first, to evaluate the vertical distribution of E. heros throughout the day, in the leaf canopy of the soybean plant, and to verify the effect of insect growth regulators (IGRs) aiming to control this pest. The study of the vertical distribution of the E. herosin the strata (upper, middle and lower) of the plants was carried out in the field condictions, where fourteen soybean plants per meter were randomly evaluated, every three hours, in the time interval between 5h, 8h, 11 am, 2 pm, 5 pm and 8 pm, for 3 non-consecutive days. In each stratum all individuals (nymphs and adults) of the stink bug was counted. The treatments consisted of the three strata of the soybean plants and the different sampling points performed at each time of the day represented the repetitions. Tests with IGR´s insecticides were conducted under laboratory conditions using the products lufenuron, teflubenzuron and novaluron with highest and lowest recommended dose of each product for caterpillars control, constituting the essay with six chemical treatments plus control (water) with six repetitions per treatment. The spraying was carried out with a CO2 sprayer using cone jet nozzles at a pressure of 45 pounds/inch2 , calibrated with spray volum of 150 L ha-1 . Spraying were carried out over sheets of filter paper placed inside plastic trays, where there were the food source (bean pods, soybean, peanut grains, sunflower grains and water). After the spraying stay dried over the sheets of paper, 14 nymphs of the fourth instar of the stink bug were placed for locomotion over treated surface, and then the number of dead nymphs, deformed nymphs, dead adults, number of eggs and adult longevity was evaluated over the days. An irregular distribution of E. heros nymphs and adults was observed in the three studied strata of soybean plants, during the day. At 11 am and 2 pm, when the ambient temperature and solar radiation were highest, both the E. heros adults and the nymphs positioned preferentially on the upper stratum of the soybean plants and later migrated to the middle and lower strata when the temperature and solar radiation decreased. Regarding the insecticides tested, novaluron in the lower dose (20.0 g a.i./ha), teflubenzuron with the higher dose (52.5 g a.i./ha) and the higher dose of lufenuron (40.0 g a.i./ha) were the treatments that provided a greater number of deformed adults. The higher number of deformed nymphs was observed when subjected to the lower dose of novaluron (20.0 g a.i./ha) with nymph mortality being significant in all chemical treatments. Lufenuron in its higher dose (40.0 g a.i./ha) was the one that most reduced insect longevity. Oviposition was null when the insects were submitted to the two doses of novaluron (20.00 g a.i./ha and 40.0 g a.i./ha) as well as with the lower and higher dose of lufenuron (20.0 gia / ha and 40.0 g a.i./ha), while with both doses of telfubenzuron (26.2 g a.i./ha and 52.5 g a.i./ha), oviposition was reduced.