Marigold (Tagetes erecta L.) as an attractive crop to natural enemies in onion fields

Abstract

Onion is the third most grown vegetable crop in São Paulo state, Brazil. Organic onion farming is expected to increase in the state due to the increasing demand. Pest management in organic onion farming is based on plant extracts with insecticide effects. However, the efficacy of such plant extracts has not been proved yet, and it was observed that they do negatively affect natural enemies. Plants surrounding onion fields, and that are attractive to natural enemies, may be a good option to farmers, since they may lead to increased diversity of arthropod species and, consequently, the natural control of pest populations. This study deals with the effect of marigold plants as a resource plant to natural enemies in onion fields. The experiment was set in a certified organic farm using marigold rows at a center of an onion field. Samples were taken from marigold and the onion plants 5 m (near) and 30 m (far) from the flowering strips. Higher numbers of arthropod pests were observed in onion plants 30 m from the marigold strip, while higher numbers of predators and parasitoids were found at 5 m distance. Species richness and Shannon's diversity index were higher at 5 m from marigold. Therefore, marigold rows next to onion fields resulted in higher number of entomophagous species, potentially enhancing the natural control of onion pests. In the study field, marigold strips may be an alternative to crop sprays for organic control of onion pests. Key words: natural control, conservation, predator, parasitoid CRAVO-DE-DEFUNTO (Tagetes erecta L.) COMO CULTURA ATRATIVA PARA INIMIGOS NATURAIS EM CULTIVO DE CEBOLARESUMO: A cebola é a terceira hortaliça mais cultivada em São Paulo, cujo cultivo orgânico tende a crescer devido ao grande mercado consumidor existente. O manejo das pragas na cebolicultura orgânica baseia-se nos extratos de plantas inseticidas que, além de terem eficiência não comprovada, podem afetar negativamente os inimigos naturais. A utilização de plantas atrativas a inimigos naturais no entorno dos cultivos de cebola pode ser uma boa opção para os produtores, pois potencialmente aumentam a diversidade da artropodofauna e podem regular naturalmente as populações de espécies pragas. Verificou-se o efeito de linhas de cravo-de-defunto (Tagetes erecta L.) como cultura atrativa a inimigos naturais em campos de cebola. O experimento foi realizado em propriedade orgânica certificada, instalando-se linhas de cravo-de-defunto nas bordaduras de dois campos de cebola. Os tratamentos foram definidos coletando-se amostras nas plantas de cebola próximas às linhas da atrativa (5m) e distante das linhas (30 m). De maneira geral, observou-se maior quantidade de artrópodes fitófagos nas plantas de cebola longe da faixa atrativa e, inversamente, maior quantidade de inimigos naturais próximos à faixa. A riqueza de espécies também foi maior nas coletas próximas, o mesmo valendo para o índice de diversidade de Shannon. Portanto, a manutenção de linhas de cravo-de-defunto próximas ao cultivo de cebola promoveu maior riqu...

Companion plants associated with kale increase the abundance and species richness of the natural-enemies of Lipaphis erysimi (Kaltenbach) (Hemiptera: Aphididae)

“…This specificity explains the decrease in parasitoid density during P2, which occurred because of the decline in the L. erysimi population within this period (Figure 4). The results obtained herein indicate that the relative abundance and species richness of the natural enemies of L. erysimi vary according to the phenology (vegetative, flowering and senescence phases) of the companion plants, thus confirming previous reports relating to species of the families Asteraceae and Apiaceae (Silveira et al, 2009;Resende et al, 2012). In general, insect populations change over time according to the availability of food resources, microclimate and shelter offered by the host plants, and these elements clearly favored the continuous richness and addition of species during the present study.…”

“…This is a promising result considering that the counting of natural enemies was performed on the kale plants themselves where predatory action against the aphids was more likely to occur. Silveira et al (2009) demonstrated that African marigolds offer conditions that favor the maintenance of natural enemies of onion pests. Climatic conditions have been shown to influence the density of L. erysimi (Bapuji Rao et al, 2013).…”

“…Members of the Asteraceae have been shown to maintain the biodiversity of predators and parasitoids when employed as a companion crop in onion fields (Silveira et al, 2009). Regarding the Apiaceae, aromatic species attract numerous insects that forage for pollen and nectar, while the floral architecture provides shelter for prey and/or preferential or alternative hosts.…”

Population of Herbivorous and Carnivorous Arthropods in Rice Field Ecosystem Modified with Vermicompost and Flower Plants

“…A study conducted by Silveira et al (2009) showed that Marigold (Tagetes erecta) planted between rows of shallots could increase the diversity of predators in the area where it was planted. Meanwhile, Entling and Dobelli (2009) and Saona et al (2011) in their research showed that carnivorous arthropods, including spiders, were more abundant in plots planted with flowering plants.…”

“…Weeds and plants which produce pollen can also be used as food source, shelter and breeds for natural enemies (Laba et al, 2000). Silveira et al (2009) stated that Marigold (Tagetes erecta L.) grown next to the main crop onions could increase the diversity of arthropods, especially the natural enemies. The abundance of hemipteran carnivore was also reported to increase in areas with flowering plants (Frank and Kunzle, 2006).…”