Toxicity to, oviposition and population growth impairments of Callosobruchus maculatus exposed to clove and cinnamon essential oils

Abstract

The use of plant essential oils has been shown to efficiently control insect pests of stored beans, significantly reducing the threats associated with synthetic insecticides. Here, we evaluated the potential of applications of essential oils of clove, Syzygium aromaticum L., and cinnamon, Cinnamomum zeylanicum L., to control Callosobruchus maculatus, considered as one of the most cosmopolitan pests of stored beans. Using four combinations of couples (i.e., unexposed couples, exposed females, exposed males, and exposed couples), we also evaluated how sublethal exposure to these essential oils impacted C. maculatus oviposition. Bioassays results revealed that both essential oils exhibited insecticidal activities similar to the synthetic pyrethroid insecticide deltamethrin. Furthermore, oil dosage increments proportionately decreased the growth rate and reduced the losses in bean weight caused by cowpea weevils, and offspring emergence was almost abolished when parents were exposed to the LD20 of each essential oil. Finally, significant oviposition impairments were perceived only in couples where females were exposed (i.e., females exposed and exposed couples) to the LD20 of cinnamon and clove essential oils. Thus, by exhibiting similar insecticidal activities as synthetic insecticides and by significantly affecting the oviposition of sublethally exposed C. maculatus females, the cinnamon and clove essential oils represent valuable tools with potential of integration into the management of C. maculatus infestations.

Fig 1. Instantaneous rate of population increase of C. maculatus exposed to clove and cinnamon essential oils.

The symbols represent the means of five replicates of the LD₀ (control), LD₂₀, LD₄₀, LD₆₀ and LD₈₀ for each oil. The doses are expressed in μL of essential oil/kg beans. The vertical bars represent the SD.

Fig 2. Bean weight losses caused by C. maculatus exposed to clove and cinnamon essential oils.

The symbols represent the means of five replicates of the LD₀ (control), LD₂₀, LD₄₀, LD₆₀ and LD₈₀ for each oil. The doses are expressed in μL of essential oil/kg beans. The vertical bars represent the SD.

Fig 3

Average emergence of C. maculatus exposed to clove (A) and cinnamon (B) essential oils. The symbols represent the means of four replicates of the LD₀ (control), LD₂₀, LD₄₀, and LD₆₀ for each oil. The doses are expressed in μL of essential oil/kg beans. The vertical bars represent the SD.

Fig 4

Normalized cumulative emergence of C. maculatus exposed to clove (A) and cinnamon (B) essential oils. The symbols represent the means of four replicates of the LD₀ (control), LD₂₀, LD₄₀ and LD₆₀ for each oil. The doses are expressed in μL of essential oil/kg beans. The vertical bars represent the SD.

Fig 5. Effects of sublethal exposure to essential oils on C. maculatus oviposition.

Number of eggs of C. maculatus females that were sublethally exposed to clove (A) or cinnamon (B) essential oils and coupled with essential oil-treated or essential oil-untreated partners. The symbols represent the means of 20 replicates (± SD) for the number of eggs laid by females of C. maculatus at three-day intervals (left panels) and the cumulative number of eggs (right panels) laid on cowpea bean masses during the first 9 days of adulthood. On the right panels, the treatments grouped by the same horizontal line did not differ according to a Tukey HSD test (P < 0.05).