Fumigant toxicity of plant essential oils against Acanthoscelides obtectus (Say) (Coleoptera: Bruchidae), an insect pest in stored bean

Worldwide losses of stored food products can reach 10% due to grain pests [1]. Acanthoscelides obtectus is well known as a pest of cultivated common beans Phaseolus vulgaris. Control is usually achieved by applying chemical insecticides [2, 3]. Thus, studies on alternative methods for chemical control as well as the biological control of these insects are necessary. Plant essential oils and their monoterpenoid major components show a broad spectrum of activity against insects, mites and various arthropods [4]. Their volatility may also be very promising for pest control because of their insecticidal properties and the fact that they can act as fumigants [5]. The present study was undertaken to investigate the effect of essential oil vapours on Acanthoscelides obtectus. The essential oils tested were: Verbena sp. Cinnamomum sp. Rosmarinus sp. and Geranium sp. Transparent acrylic cups (6,5 cm x 3,5 cm) were used for determination of volatile phase effects of the essential oils. The essential oils were applied with a micropipette on cotton strip attached to the lids. Six replicates were used for each dose (0, 5, 10, 20, 30 (µl)) of essential oil. Ten adult insects were introduced to each cup and cups were kept under controlled conditions for 24h (26 ± 2 ° C, 60 ± 5% RH). Effects of different doses on the mortality of A. obtectus adults are shown in Figure 1. At a dose of 5 µl, all the oils tested showed a toxicity that killed more than 50% of adult insect within 24h following exposure. Rosmarinus sp. showed the highest insecticidal effects, causing high adult mortalities at the lower dose (5 µl = 98,33 mortality) in comparison to other essential oils tested. It was observed that the insect mortality of essential oil of Verbena sp. at 20 µl reached 100%, while 20 µl of Cinnamomum sp. reached 90% and Geranium sp., 80%. Results of the present study revealed that plant essential oils can be an alternative to conventional insecticides for controlling insect damage to stored food.

Fig. 1: Toxicity of essential oil vapours to Acanthoscelides obtectus. 24h exposure. Values with different letters are considered significantly different (p ≤0,05, test DMS).

Acknowledgements: CAPES Foundation, Ministry of Education of Brazil, Brasilia-DF 70040 – 020, Brazil. Scholarship CAPES -Proc. n° BEX 1252/13 – 5.

Keywords: Essential oil, pest of stored, Acanthoscelides obtectus.

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