Mechanism and synergy evaluation of a mixture of croton essential oil and Spirodiclofen on Phenacoccus solenopsis (Hemiptera: Pseudococcidae)

Abstract

As a major invasive injurious insect, Phenacoccus solenopsis Tinsley poses a significant threat to cotton production. The presence of a wax coating on P. solenopsis impedes the efficacy of insecticides and contributes to the development of chemical pesticide resistance. Therefore, the synergistic effect and mechanism of croton essential oil (Co) and its components were investigated in combination with spirodiclofen, which has shown a superior synergistic effect on wax, to effectively manage this pest and mitigate the development of resistance. The compounds Co, α-pinene, fenchyl alcohol, and camphene exhibited favorable solubility in the wax secretions of mature female P. solenopsis, leading to a notable synergistic impact on spirodiclofen. The measured contact angles between the essential oil mixtures and beeswax were 22.27°, 26.94°, 29.72°, and 19.37°. The penetration levels of spirodiclofen were 1.65, 1.47, 1.26, and 1.45 μg, resulting in synergistic ratios of 3.51, 3.51, 3.11, and 3.37, and the inhibitory effect of increased essential oils on GST activity was 36.53%, 30.48%, 54.22% and 59.38%, respectively. The results showed that when used in combination with spirodiclofen, these compounds alone or in combination reduced the GST activity of the females, with the best synergistic effect of fenchyl alcohol with spirodiclofen, and Co and its constituents showed good synergistic effect. Thus, this method shows good potential for the development of additives and the results proved a new material source for green pest control.