RESUMO O objetivo deste trabalho foi avaliar o comportamento de oviposição de Helicoverpa armigera confinadas em diferentes densidades de casais e estádios fenológicos de plantas de soja, e a resistência de genótipos de soja na categoria não preferência para oviposição para H. armigera. Para o comportamento de oviposição de H. armigera, foram avaliadas as densidades de um, dois e quatro casais por planta, e os estádios fenológicos vegetativo, de florescimento e reprodutivo de plantas de soja do cultivar BR 16. Para o teste de não preferência para oviposição, oito genótipos de soja foram utilizados e um índice de preferência para oviposição foi calculado. A densidade de tricomas nos folíolos foi quantificada para ser correlacionada com a oviposição de H. armigera. A densidade de um casal e plantas de soja em estádio reprodutivo proporcionaram os melhores resultados quanto à preferência para oviposição de H. armigera em soja. Os genótipos M8230 RR e W711 RR apresentaram características de resistência, enquanto o PI 227687 foi o mais preferido para oviposição. A quantidade de tricomas influenciou positivamente no comportamento de oviposição das fêmeas.

ABSTRACT The objective of this study was to evaluate the oviposition behavior of Helicoverpa armigera confined in different adult pair density and growth stages of soybean plants, and the resistance of soybean genotypes to H. armigera in the category nonpreference for oviposition. The oviposition behavior of H. armigera was assessed using one, two, and four adult pairs per soybean plant of the cultivar BR-16 at the growth stages: vegetative V8 (eighth unrolled trifoliate leaf), reproductive R2 (full bloom) and reproductive R5.2 (beginning seed). The nonpreference for oviposition was evaluated using eight soybean genotypes and an oviposition preference index was calculated. The number of trichomes in leaflets was quantified for being correlated to H. armigera oviposition. One adult pair and soybean plants stage at pod-set affected and showed the best results oviposition preference on soybean plants. The genotypes M8230-RR and W711-RR presented resistance characteristics, and PI-227687 was preferred for oviposition. The trichome density positively affects the female oviposition behavior.

Resumen Las chinches son consideradas importantes plagas de la soya al causar daños que afectan su producción y comercialización. La determinación de los umbrales de acción para el control de estas plagas garantiza una mayor seguridad en el uso de insecticidas. El objetivo de este estudio fue evaluar el umbral de acción en el manejo de las chinches de la soya y su influencia en los parámetros fitotécnicos y fisiológicos y en el parasitismo de huevos de las chinches. El experimento se instaló en campo, en bloques al azar, utilizando el cultivar Anta 82 RR. Los tratamientos tuvieron cinco umbrales de acción para las chinches fitófagas: 0,5 chinches/m, 1,0 chinche/m, 2,0 chinches/m, 4,0 chinches/m y el control (sin aplicación de insecticidas), con cuatro repeticiones. El muestreo de las chinches se llevó a cabo a través del método del paño vertical y para evaluar el parasitismo se realizaron muestreos semanales de los huevos de las chinches. Los parámetros fisiológicos y fitotécnicos que se evaluaron fueron los siguientes: productividad (kg/ha), peso de 100 semillas, índice de daño a las vainas (%), retención de la hoja, vigor, viabilidad y daño en las semillas. Se observó que los niveles de acción más severos contra chinches influenciaron positivamente en los parámetros fitotécnicos y fisiológicos de la soya, así como el número de semillas por vaina, semillas por planta y vainas por planta. Además el nivel de acción de 1,0 chinche/m es el más indicado para el tratamiento de los chinches de la soya; sin embargo, el parasitismo en este nivel de acción tiende a ser bajo.

Abstract Stink bugs are major soybean pests, causing damage that affects grain production and marketing. Determining action thresholds for pest control can improve the proper use of insecticides on these pests. This study aimed to evaluate five action thresholds for the management of stink bugs on soybeans, as well as their influence on phytotechnical and physiological parameters as well as on parasitism of stink bug eggs. This study was conducted in the field utilizing a completely randomized block design, using the soybean cultivar ‘Anta 82 RR’. Insecticide application treatments consisted of five action thresholds used against phytophagous stink bugs: half stink bug.m-1, one stink bug.m-1, two stink bugs.m-1, four stink bugs.m-1 and control (no insecticide sprayed), and four replications. Insect sampling was carried out using the beat cloth method, and parasitism evaluations were also taken weekly by conducting stink bug egg samplings. Soybean physiological and phytotechnical parameters, including crop yield (kg.ha-1), 100-seed weight, pod damage index PDI (%), leaf retention, plant vigor, seed viability and damage, number of seeds per pod, seeds per plant, and pods per plant were also assessed. It was observed that the most severe action thresholds used on stink bugs most positively influenced crop phytotechnical and physiological parameters. Moreover, it was noted that one stink bug.m-1 is the optimal action threshold for stink bug management on soybeans, even though egg parasitism at this level tended to be lower.