ABSTRACT Interspecific competitions are important mechanisms in structuring ecological communities, including agroecosystems, in which different species may share the same food resource. In melons, two major pests coexist in time and space, Liriomyza sativae Blanchard (Diptera: Agromyzidae) and Bemisia tabaci (Gennadius) (Hemiptera: Aleyrodidae). The former feeds on the leaf mesophyll, while the latter on the phloem sap. Therefore, the same niche exploitation can trigger interactive processes between both populations. The present research aimed to determine if there are positive or negative interactions between whiteflies and leafminers under field conditions. The experiment was conducted in four commercial melon fields in northeast Brazil in two planting seasons. Thirty random plants were weekly selected for detection of whitefly nymphs and leafminer larvae throughout the entire crop cycle. The data was organized and analyzed considering the species abundance of L. sativae (larvae) and B. tabaci (nymphs and adults) in the same plant. Thus, the coabundance of species was investigated by using regressions with Poisson errors. The results suggest different fractions of negative, positive and neutral (not significant relationships) coabundance between the two species. Among 34 significant interactions, 56% were negative, suggesting that more than half of significant interactions are due to interspecific competition with negative coabundance.

RESUMO Liriomyza sativae (Blanchard) é uma praga polífaga de distribuição mundial em hortaliças e plantas ornamentais, cujo controle químico é o principal método adotado. Entretanto, inseticidas botânicos na forma de óleos essenciais (OEs) são apresentados como alternativas promissoras. Objetivou-se avaliar o efeito de OEs das espécies Croton sonderianus Muell. Arg., Croton conduplicatus Kunth., Lippia gracilis Schauer e Lippia schaueriana Mart. sobre aspectos biológicos de adultos e estágios imaturos (larva e pupa) de L. sativae. Os resultados demonstram mortalidade larval e pupal após imersão de folhas com larvas recém-eclodidas de L. sativae em soluções de OEs de folhas de L. gracilis e L. schaueriana. Os OEs de casca e folha de C. conduplicatus e de casca de C. sonderianus prolongaram o período de pupa da mosca-minadora, enquanto os de folhas de C. conduplicatus e casca de C. sonderianus causaram redução na oviposição e puncturas de alimentação em testes de confinamento. Apenas C. conduplicatus confirmou o efeito no teste com livre chance de escolha, mostrando-se como o mais promissor do estudo. Desta forma, OEs de folhas de L. gracilis e L. schaueriana possuem atividade inseticida sobre larvas de L. sativae e os de folhas de C. conduplicatus reduzem a oviposição e as puncturas de alimentação de mosca-minadora em meloeiro.

ABSTRACT Liriomyza sativae (Blanchard) is a worldwide polyphagous pest for horticultural and ornamental crops, whose chemical control is the major method adopted. However, botanical insecticides in the form of essential oils (EOs) are presented as promising alternatives. This study aimed to evaluate the effect of EOs from the species Croton sonderianus Muell. Arg., Croton conduplicatus Kunth., Lippia gracilis Schauer and Lippia schaueriana Mart. on the biological aspects of L. sativae adults and immature stages (larva and pupa). The results showed larval and pupal mortality after the immersion of leaves with newly hatched L. sativae larvae in EOs solution from L. gracilis and L. schaueriana leaves. The EOs from C. conduplicatus stem bark and leaf and from C. sonderianus stem bark extended the leafminer pupal stage duration, while those from C. conduplicatus leaves and C. sonderianus stem bark decreased the oviposition and feeding punctures in no-choice tests. Only C. conduplicatus confirmed the effect in the free-choice test, showing to be the most promising in the study. This way, EOs from L. gracilis and L. schaueriana leaves show an insecticide activity on L. sativae larvae, and those from C. conduplicatus leaves reduce the leafminer oviposition and feeding punctures in melon plants.