Incidence of natural control agents of the velvetbean caterpillar and response of its predators to insecticide treatments in Brazilian soybean fields

Lagartas de Anticarsia gemmatalis Hubner foram coletadas em soja (Glycine max (L.) Merrill) para determinar os níveis populacionais e a porcentagem de infecção pelo fungo-Nomuraea rileyi (Farlow) Samson. Os níveis populacionais de larvas e adultos do predador Colosoma argentatus granulatum (Perty) foram determinados utilizando armadilhas de solo. Foi estudada a relação entre a ressurgência de A. gemmatalis e os níveis populacionais dos predadores C. argentatus granulatum, Geocoris spp. e Nabis spp. sob influência de inseticidas. A infestação pelo fungo N. rileyi começou em fevereiro, durante o estágio de desenvolvimento dos legumes quando a terceira geração de lagartas alcançou o seu pico. Três semanas mais tarde 100% das lagartas observadas sobre as folhas estavam infectadas pelo fungo. A atividade de C argentatus granulatum coincidiu com o pico da terceira geração de A. gemmatalis. As populações de Geocoris spp. e Nabis spp. foram severamente afetadas com as aplicações de monocrotofos e metilparation, mas a aplicação diflubenzuron, um inibidor da formação de quitina, aparentemente não provocou efeito deletério.Larvae of the velvetbean caterpillar Anticarsia gemmatalis Hubner were collected from soybean (Glycine max (L.) Merrill) to determine their population levels and percentage of infection by the fungus, Normuraea rileyi (Farlow) Samson. Seasonal population levels of larvae and adults of the carabid predator, Calosoma argentatus granulatum (Perty) were determined by pitfall trap collections. The relationship between resurgence of Anticarsia and populations of Calosoma, geocorids, and nabids as influenced by insecticides was studied. Fungus attack began in February during the pod development stage when the third generation of Anticarsia larvae were reaching a peak and 100% of larvae observed on foliage were infected three weeks later. Activity of Colosoma coincided closely with population levels of the third generation of Anticarsia. Geocorid and nabid populations were severely affected by monocrotophos and methyl parathion treatments whereas diflubenzuron, a chitin inhibitor, had no apparent deleterious effect

Retençáo foliar em plantas de soja (\u3ci\u3eGlycine max\u3c/i\u3e (L.) Merrill), resultante da açáo de \u3ci\u3ePiezodorus guildinii\u3c/i\u3e (Westwood, 1837) (Hemiptera, Pentatomidae), em diferentes níveis e épocas de infestaçáo

Foliar retention in soybean (Glyaine max (L.) Merril) as effected by levels and period of infestation with Piezodorus guildinii (Westwood, 1837) (Herniptera, Pentatornidae) The effect of stinkbug on foliar retention in soybean was studied. Field tests were carried out in Guaiba, Rio Grande do Sul, 1974/75. Soybean plants were artificially infested at various densities of Piezodorus guildinii (Westwood, 1837), per 0,5m of row and at different stages of soybean development by means of isolation cages. Foliar retention occurred when plants were infested continuosly, from full to the complete physiological maturity of the seed. This phenomenon was not observed when infestations were restricted only from bIoom to the beginning of pod formation. Infestations restricted to the period of seed development required at least six bugs/m of row to cause foliar retention, while those restricted to the period of physiological maturation of the seed required at least 10 bugs/m of row. Dentre os problemas da cultura da soja, destaca-se a ação de varios insetos fitófagos, entre esses os pentatomídeos que afetam negativamente o indice de produtividade. Os pentatomideos acasionam danos a apreciaveis, sendo responsaveis pela redução do rendimento e qualidade da semente, como tambem pela ocorrência de retenção foliar. Esta consiste num atraso da maturação das plantas, permanecendo verdes as folhas, hastes e legumes após o período normal de maturação e, paralelamente, na formação de legumes chochos com sementes abortadas (DAUGHERTY et alii, 1964; GOMES, 1966: QUEIROZ et alii, 1971: ROWAN & PEREIRA, 1971; RIZZO, 1972; SINGH, 1973; CORSEUIL et alii, 1974; TODD & TURNIPSEED, 1974; PANIZZI, 1975; CORSO et alii, 1975). A retenção foliar tambem e referida como soja louca (VERNETTI et alii, 1969; GALLO et alii, 1970)