RESUMO

The Neotropical brown stink bug Euschistus heros (F.) can reach high densities in some soybean areas in Brazil. Besides soybean, it also feeds on other plants, but little is known on the alternative hosts of E. heros in Rio Grande do Sul state. In this study, wild non-cultivated hosts of E. heros at Norwest of Rio Grande do Sul state were determined, and the E. heros performance was compared when fed on soybean and on wild hosts. Bugs were sought in plants located inside and on the edge of soybean fields during 2004/2005 and 2005/2006 seasons. Adults were recorded feeding on seeds of Amaranthus retroflexus (Amaranthaceae), and on fruits of three Solanaceae, mainly Vassobia breviflora. Immature survivorship on soybean (86.7%) and on V. breviflora (81.8%) was the same, but nymphs fed on A. retroflexus did not reach adulthood. The host plant used during immature development greatly affected adult weight, with V. breviflora yielding the heaviest adults; however, adult survivorship and longevity when fed on different host plants were the same. Females fed on soybean laid larger egg masses than those fed on V. breviflora , but the overall fecundity was not affected.

Assuntos

RESUMO

O percevejo marrom da soja, Euschistus heros (F.), pode atingir altas densidades em alguns locais. Além da soja, alimenta-se de outras plantas, mas pouco se sabe sobre seus hospedeiros alternativos no Rio Grande do Sul. Os objetivos deste estudo foram determinar os hospedeiros nativos utilizados por E. heros no Noroeste do Rio Grande do Sul e comparar seu desempenho quando alimentado com estes e com a soja. Os percevejos foram amostrados em plantas existentes em áreas internas e marginais de cultivos de soja, nas safras 2004/2005 e 2005/2006. Euchistus heros foi encontrado alimentando-se de sementes de Amaranthus retroflexus (Amaranthaceae) e de frutos de três Solanaceae, principalmente Vassobia breviflora. A sobrevivência dos imaturos alimentados com soja (86,7 por cento) e com V. breviflora (81,8 por cento) foi semelhante, mas ninfas alimentadas com A. retroflexus não atingiram o estágio adulto. O alimento das ninfas teve efeito significativo sobre o peso dos adultos, o qual foi maior para aquelas alimentadas com soja do que com V. breviflora . Por outro lado, a sobrevivência e longevidade dos adultos não diferiram significativamente. As fêmeas alimentadas com soja depositaram massas de ovos maiores do que aquelas alimentadas com V. breviflora, mas não houve efeito do hospedeiro no numero médio de massas de ovos depositado/fêmea.

The Neotropical brown stink bug Euschistus heros (F.) can reach high densities in some soybean areas in Brazil. Besides soybean, it also feeds on other plants, but little is known on the alternative hosts of E. heros in Rio Grande do Sul state. In this study, wild non-cultivated hosts of E. heros at Norwest of Rio Grande do Sul state were determined, and the E. heros performance was compared when fed on soybean and on wild hosts. Bugs were sought in plants located inside and on the edge of soybean fields during 2004/2005 and 2005/2006 seasons. Adults were recorded feeding on seeds of Amaranthus retroflexus (Amaranthaceae), and on fruits of three Solanaceae, mainly Vassobia breviflora. Immature survivorship on soybean (86.7 percent) and on V. breviflora (81.8 percent) was the same, but nymphs fed on A. retroflexus did not reach adulthood. The host plant used during immature development greatly affected adult weight, with V. breviflora yielding the heaviest adults; however, adult survivorship and longevity when fed on different host plants were the same. Females fed on soybean laid larger egg masses than those fed on V. breviflora , but the overall fecundity was not affected.

Assuntos

RESUMO

Plant trichomes can difficult the attachment and movement of small insects. Here, we examine the hypothesis that the success on the use of densely haired hosts by two cassidine species is determined by differential morphology and behavior. Larvae of Gratiana graminea (Klug, 1829) and Gratiana conformis (Boheman, 1854) move on the leaf surface of their host, Solanum guaraniticum Hassl by anchoring their tarsungulus on the trichome rays or by inserting the tarsungulus tip directly into epidermis. This kind of movement is only possible due to a similar tarsungulus shape among the species. Tarsungulus growth pattern is also similar between species, being relatively small on the posterior aperture, matching the diameter of the host plant trichome rays. The tarsungulus shape associated with differences on ontogenetic growth and attachment pattern allow these two Cassidinae larvae to efficiently move on the pubescent leaf surface of their host.

Os tricomas foliares podem dificultar a fixação e o movimento de pequenos insetos. Neste trabalho, testamos a hipótese de que o sucesso na exploração de plantas com folhas densamente cobertas por tricomas é determinado pela morfologia e comportamento diferenciados em duas espécies de cassidíneos. As larvas de Gratiana graminea (Klug, 1829) e Gratiana conformis (Boheman, 1854) se movem sobre a superfície foliar de sua hospedeira, Solanum guaraniticum Hassl através do ancoramento de seus tarsúngulos no raio dos tricomas estrelados da planta ou da inserção da ponta desta estrutura diretamente na epiderme. Tais tipos de movimento só são possíveis devido à forma dos tarsúngulos, a qual é similar nas duas espécies. O padrão de crescimento dos tarsúngulos das espécies estudadas é também similar e apresenta-se relativamente menor na abertura posterior, correspondente ao diâmetro dos raios dos tricomas estrelados. A forma dos tarsúngulos, associada às diferenças no seu padrão de crescimento permite às larvas destas duas espécies de Cassidinae se moverem com eficiência sobre a superfície pubescente de sua planta hospedeira.

Assuntos

RESUMO

Gratiana spadicea(Klug) (Coleoptera, Chrysomelidae) is a monophagous beetle that feeds only on leaves of Solanum sisymbriifolium Lamarck (Solanaceae). We determined the portions of S. sisymbriifolium leaves that are used by the adults as feeding and oviposition sites. Daily variation on larval and adult feeding frequency, and on oviposition, was also registered under laboratory conditions (25oC; 70+10% rh). Larvae and adults were fed with S. sisymbriifolium leaves during photo (14 hours) and scotophase (10 hours). At the end of each phase, it was measured the leaf area they ate and registered position of their feeding marks on leaves. The oothecae were counted and noted, regarding their position on the leaf blade. Larvae and adults of G. spadicea showed feeding activity during photo and scotophase. Oviposition was restricted to photophase. Females leaf consumption rates were greater than those of the males. Adult feeding marks were most frequent on leaf margins. Oothecae were most frequently found near the central vein of the abaxial leaf surface. Daily ingestion rates grew exponentially through the larval stage; fifth instar ingested more than 60% of the total amount of food consumed by the larval stage. The possible adaptive mechanisms involved in such feeding and oviposition patterns are discussed.

RESUMO

Gratiana spadicea(Klug) (Coleoptera, Chrysomelidae) is a monophagous beetle that feeds only on leaves of Solanum sisymbriifolium Lamarck (Solanaceae). We determined the portions of S. sisymbriifolium leaves that are used by the adults as feeding and oviposition sites. Daily variation on larval and adult feeding frequency, and on oviposition, was also registered under laboratory conditions (25oC; 70+10% rh). Larvae and adults were fed with S. sisymbriifolium leaves during photo (14 hours) and scotophase (10 hours). At the end of each phase, it was measured the leaf area they ate and registered position of their feeding marks on leaves. The oothecae were counted and noted, regarding their position on the leaf blade. Larvae and adults of G. spadicea showed feeding activity during photo and scotophase. Oviposition was restricted to photophase. Females leaf consumption rates were greater than those of the males. Adult feeding marks were most frequent on leaf margins. Oothecae were most frequently found near the central vein of the abaxial leaf surface. Daily ingestion rates grew exponentially through the larval stage; fifth instar ingested more than 60% of the total amount of food consumed by the larval stage. The possible adaptive mechanisms involved in such feeding and oviposition patterns are discussed.