Effects of Entomopathogenic Fungi on Individuals as Well as Groups of Workers and Immatures of Atta sexdens rubropilosa Leaf-Cutting Ants

In 2009, sulfluramid, the main ingredient in toxic baits for leaf-cutting ant control, was included in Annex B of the Stockholm Convention on Persistent Organic Pollutants. This resulted in interest in the use of entomopathogenic fungi such as Beauveria bassiana and Trichoderma harzianum for leaf-cutting ant control. The efficiency of these fungi in controlling these insects and the way that ants react individually or in group to the biological risks posed by these fungi is poorly understood. For this reason, we assessed the effects of B. bassiana and T. harzianum on Atta sexdens rubropilosa larvae, pupae and workers. Moreover, we investigated whether the number of contaminated individuals within a group has an influence in controlling the spread of fungi among workers. We found that the fungus T. harzianum showed high pathogenicity against A. sexdens rubropilosa larvae and pupae, leading to faster mortality and a survival rates. On the other hand, the fungus B. bassiana was responsible for causing faster worker mortality and lower survival rates. In addition, we observed that an increase in individuals contaminated with B. bassiana or T. harzianum in the group decreases its survival rate. The results support the hypothesis that entomopathogenic fungi are efficient in controlling leaf-cutting ants when contaminated workers are allocated to groups of healthy workers.

Bioactivity of Asclepias curassavica, Equisetum spp. and Rosmarinus officinalis Extracts Against Leaf-Cutting Ants

Chemical control of leaf-cutting ants is widely used, but alternative control with toxic plant extracts is promising. Substances with insecticidal potential extracted from plants have numerous ecological advantages. This study evaluated the insecticidal and/or fungicidal potential of the plants Asclepias curassavica (tropical milkweed), Rosmarinus officinalis L. (Lamiaceae) (rosemary) and Equisetum spp. (horsetail) for control of the leaf-cutting ant Atta sexdens rubropilosa Forel, 1908 (Hymenoptera: Formicidae). Forty laboratory-reared colonies of Atta sexdens rubropilosa were used. The plants were collected, dried out in a circulating air oven for 48 hours, ground, and macerated in 96o ethanol until exhaustion. After filtration, the products were evaporated under reduced pressure to obtain the ethanolic extracts. Acceptance of the reagent, topical application of the extracts, and application of baits containing 4% of the plant extracts were tested. The results showed that all plant extracts tested negatively influenced the development of the fungus garden. Baits produced with Asclepias curassavica caused the highest mortality of the colonies within 7 days. In conclusion, the ethanolic extracts of Asclepias curassavica, Rosmarinus officinalis and Equisetum spp. exhibit insecticidal (contact and ingestion) and fungicidal activity in colonies of the leaf-cutting ant Atta sexdens rubropilosa.

Preferência de Atta sexdens rubropilosa Forel (1908) (Hymenoptera: Formicidae) por espécies e híbridos de eucalipto

Este trabalho teve como objetivo avaliar a preferência de Atta sexdens rubropilosa Forel (1908) por diferentes espécies e híbridos de eucalipto, provenientes de diferentes localidades do estado do Mato Grosso. Foram coletadas amostras foliares de 21 tratamentos plantados nos municípios de Itiquira, Santa Rita do Trivelato e Sinop. Os testes de atratividade foram feitos em campo no município de Cuiabá (MT). Para os testes de atratividade, foram utilizadas placas de alumínio numeradas, sendo que cada espécie, clone ou híbrido foram considerados como tratamento. Em cada placa de alumínio, foram colocados 25 discos foliares de cada tratamento e as placas foram dispostas ao longo do carreador ativo dos formigueiros, sendo quatro repetições por tratamento. A atratividade foi avaliada, determinando-se a quantidade de discos foliares transportados dos tratamentos. As saúvas apresentaram maior preferência foliar pelos híbridos Eucalyptus urophyla x Eucalyptus grandis (urograndis). Eucalyptus camaldulensis e Corymbia citriodora foram as espécies com menor preferência, podendo afirmar que espécies seminais apresentam menor preferência de carregamento pelas formigas em comparação com as clonais. As regiões onde os eucaliptos foram plantados afetam na preferência de carregamento foliar pelas formigas, sendo os situados em Santa Rita do Trivelato os que apresentaram maior preferência de carregamento.

TOXICITY OF Esenbeckia pumila Pohl (Rutaceae) ON Artemia salina AND Atta sexdens rubropilosa

ABSTRACT The number of studies on plant compounds with insecticidal activity has increased in recent years, and one of the primary targets of these compounds is leaf-cutter ants, which are considered the most important pests in Brazilian plantations, especially ants of the genus Atta. The objective of this study was to evaluate the toxic activity of the crude extract and fractions of the leaves of Esenbeckia pumila Pohl (Rutaceae) on Artemia salina and Atta sexdens rubropilosa and to perform a phytochemical study of this plant species. The toxicity of the extract and fractions was evaluated by determining the mean lethal concentration (LC50) on A. salina. The insecticidal activity was evaluated by feeding the ants an artificial diet containing the crude extract or fractions, and the results were analyzed using the log-rank test. The substances were isolated by chromatography, and the molecular structure was determined by spectroscopy. In the bioassay with A. salina, the ethanol extract and dichloromethane and ethyl acetate fractions were highly toxic. The analysis of survival curves indicated that the mortality rate of A. sexdens rubropilosa workers fed different fractions was higher than that of ants fed the control diet, especially the ethyl acetate fraction, with a mean survival time of 3 days and cumulative mortality of 100% on day 21 (p<0.05). The phytochemical study of this plant species allowed isolating the flavonoid rutin and a mixture of the triterpenes α-amyrin, β-amyrin, and lupeol. These results suggest the insecticidal potential of E. pumila on Atta sexdens rubropilosa.