Behavioral and Electrophysiological Effects of Ajowan (Trachyspermum ammi Sprague) (Apiales: Apiaceae) Essential Oil and Its Constituents on Nymphal and Adult Bean Bugs, Riptortus clavatus (Thunberg) (Hemiptera: Alydidae)

Abstract

We investigated the repellent effect of 12 Apiaceae plant essential oils on nymphal and adult (male and female) forms of the bean bug, Riptortus clavatus (Thunberg) (Hemiptera: Alydidae), using a four-arm olfactometer. Among the essential oils tested, ajowan (Trachyspermum ammi Sprague) essential oil showed the strongest repellent activity against the nymphal and adult bean bugs. For female adults, the repellent activity was significantly different between an ajowan oil-treated chamber and an untreated chamber down to a concentration of 14.15 μg/cm2. We also investigated the repellent activity of individual ajowan essential oil constituents. Of the compounds examined, carvacrol and thymol showed the most potent repellent activity against the nymphal and adult bean bugs. Carvacrol and thymol exhibited 73.08% and 70.0% repellent activity for the bean bug nymph at 0.71 and 2.83 μg/cm2, respectively, and 82.6% and 80.7% at 5.66 and 11.32 μg/cm2, respectively, for male adults. Carvacrol and thymol exhibited strong repellent activity against female adult bean bugs down to a concentration of 2.83 μg/cm2. Ajowan essential oil, thymol and carvacrol elicited a negative electroantennogram (EAG) response from adult bean bugs. This could explain the repellent activity of ajowan essential oil and its constituents. Our results indicate that ajowan essential oil and its constituents carvacrol and thymol can be potential candidates as the ‘push’ component in a ‘push-pull’ strategy for bean bug control.

Inhibitory effect of thymol on pheromone-mediated attraction in two pest moth species

“…In contrast, p -cymene exerted an antagonistic effect when mixed with thymol, overriding the disruptive effect of the latter in both species. As previously stated, carvacrol by its own exerts repellency on insects 18 , 23 , 25 . Nonetheless, it must be taken into consideration that relatively low dosages (1.5–3 µg) were tested, and thus additional trials would be necessary to state consistent conclusions.…”

“…Here we provide evidence of the activity of thyme oil and its major component thymol as disruptors of the sex pheromone attractiveness on G. molesta and S. littoralis males. Thymol is abundantly found in EOs of Lamiaceae 41 , Verbenaceae 24 , and Apiaceae 23 , among other plant families. Toxic and repellent activity of thymol on arthropod pests of agricultural and medical-veterinary importance has been well documented 18 , 42 .…”

“…Toxic and repellent activity of thymol on arthropod pests of agricultural and medical-veterinary importance has been well documented 18 , 42 . For example, thymol is strongly repellent to the bean bug Riptortus clavatus (Thunberg) (Hemiptera: Alydidae) 23 , and Sitophilus zeamais (Motschulsky) (Coleoptera: Curculionidae) 24 . In S. littoralis , thymol is an acute toxic for larvae 43 , and also affects the behavior of adult females.…”

“…A stimulus of 10 2 µg of either thymol or carvacrol evoked a negative–positive response in males and females of both species, and both compounds resulted to be an antifeedant for immature stages. Recently, Lee et al 23 obtained reversed EAG profiles from R. clavatus in response to 10 3 µg of thymol and carvacrol, and both compounds were strongly repellent to females. These findings are partially in accordance with ours.…”

“…In terms of repellency, several authors have reported the effect of thyme on different insect orders, including Diptera 16 – 18 , Coleoptera 19 , Hemiptera 20 , 21 , and Thysanoptera 22 . In this regard, the two phenolic monoterpenes thymol and carvacrol have been suggested to be repellent for different insect species 18 , 23 – 25 . In mosquitoes (Diptera: Culicidae), for instance, the repellency evoked by thyme on Culex pipiens pallens Coquillet is attributable to both phenolic monoterpenes and α-terpinene 18 , while the repellent effect of three Lamiaceae species against Aedes albopictus Skuse is associated to carvacrol 25 .…”