Electrophysiological and behavioural responses of Stegobium paniceum to volatile compounds from Chinese medicinal plant materials.

BACKGROUND: Stegobium paniceum (Coleoptera, Anobiidae) is an important pest of stored products causing severe damage to dried Chinese medicinal plant materials (CMPMs). Plant volatiles play an important role in host-searching of insects. The olfactory responses of S. paniceum to the most abundant volatile components of some drugstore attractant CMPMs such as Panax notoginseng, Angelica sinensis, Gastrodia elata and Peucedanum praeruptorum, namely falcarinol, 3-n-butylphthalide, p-cresol and ß-pinene, respectively, were studied by electroantennography (EAG) and behavioural bioassays in six- and four-arm olfactometers. RESULTS: EAG recordings showed that male and female antennae are able to perceive the test compounds in a wide range of concentrations and in a dose-dependent manner. Moreover, for each dose of different compounds tested, no significant differences were found between the mean male and female EAG responses. In six-arm olfactometer bioassays, S. paniceum exhibited positive responses to falcarinol, 3-n-butylphthalide, p-cresol and ß-pinene at doses of 1, 10, 100, 500 and 1000 µg. The most attractive dose was 500 µg for falcarinol, 100 µg for 3-n-butylphthalide, 500 µg for p-cresol and 1000 µg for ß-pinene. Olfactory preferences of S. paniceum, based on comparison of these four compounds at their optimally attractive concentrations in a four-arm olfactometer, were 3-n-butylphthalide > p-cresol > falcarinol > ß-pinene. CONCLUSION: The results indicated that the four volatiles of CMPMs are perceived by the peripheral olfactory system of S. paniceum adults and are able to individually elicit a positive chemotaxis in S. paniceum adults confirming the role of chemical cues in host-plant detection and selection of this pest. Further field studies are needed to evaluate the potential of the attractive compounds identified in this study, particularly 3-n-butylphthalide, to be applied as a novel monitoring and control tool against this storage-beetle pest. © 2022 The Authors. Pest Management Science published by John Wiley & Sons Ltd on behalf of Society of Chemical Industry.

Bioactivity of Wild Hop Extracts against the Granary Weevil, Sitophilus granarius (L.).

The use of bioinsecticides, rather than synthetic compounds, appears a goal to be pursued in pest control, especially for species such as Sitophilus granarius (L.) which attack stored products. Since Humulus lupulus (L.) is a remarkable source of bioactive compounds, this study investigated the bioactivity of hop flower extracts against S. granarius adults by evaluating toxic (contact, inhalation, and ingestion), repellent, antifeedant, and nutritional effects as well as their anticholinesterase activity and olfactory sensitivity. Hop extracts were obtained by soaking dried and ground hop cones in solvents of decreasing polarity: methanol, acetone, and n-hexane. Dried crude extracts were resuspended in each solvent, and used in topical application, ingestion, and fumigation toxicity assays, as well as in contact and short-range repellency tests, in vitro anticholinesterase activity evaluation, and electroantennographic tests. No inhalation toxicity for the extracts was found. On the contrary, all extracts showed adult contact toxicity 24 h after treatment (LD50/LD90 16.17/33.20, 25.77/42.64, and 31.07/49.48 µg/adult for acetone, n-hexane, and methanol extracts, respectively); negligible variations for these values at 48 h were found. The anticholinesterase activity shown by all extracts suggested that the inhibition of this enzyme was one of the mechanisms of action. Interestingly, flour disk bioassays revealed a significant ingestion toxicity for the acetone extract and a lower toxicity for the other two extracts. Moreover, all extracts affected insect nutritional parameters, at the highest dose checked. Filter paper and two-choice pitfall bioassays showed repellent activity and a strong reduction of insect orientation to a highly attractive food odor source, with minor differences among extracts, respectively. Finally, the presence of volatile compounds in the different extracts that are perceived by insect antennae was confirmed by electroantennography. All these findings strongly suggest a possible use of hop cone extracts against S. granarius, thus further confirming this plant as an interesting species for pest control.

Innate positive chemotaxis to paeonal from highly attractive Chinese medicinal herbs in the cigarette beetle, Lasioderma serricorne.

Lasioderma serricorne, also known as cigarette beetle, can exploit a wide variety of stored materials as foods, but it is particularly common on tobacco and herbs. This beetle is a dominant pest species of stored Chinese medicinal materials (CMMs) causing high economic damages, making effective control strategies urgently needed. Behavioural manipulation is an important component of Integrated Pest Management. To the best of our knowledge, plant-borne volatile organic compounds (VOCs) have never been explored to develop lures for managing L. serricorne. In this study, the behavioural responses of L. serricorne to VOCs from four selected CMMs (Euphorbia kansui, Aconitum carmichaelii, Eucommia ulmoides and Pinellia ternata) were studied and their components analysed. Then, the olfactory responses of L. serricorne to the most abundant VOC identified in the preferred CMM, i.e., paeonal, was tested. L. serricorne showed significant differences in its preferences for the VOCs from the four CMMs, i.e, E. kansui > A. carmichaelii > E. ulmoides > P. ternata. From the VOCs of E. kansui, A. carmichaelii, E. ulmoides, and P. ternata, 77, 74, 56, and 81 molecules, were identified, respectively. Paeonal (23.5%), junipene (17.2%), hexanal (17.1%), and benzeneacetonitrile (14.0%) were the most abundant, respectively. Since paeonal dominated the VOC spectrum of the most preferred CMM, this compound was selected for further studies. L. serricorne showed significant positive responses to paeonal tested at various doses, with the most attractive ones being 100 µg and 500 µg. Our findings shed light on the olfactory cues routing the food searching behaviour in the cigarette beetle, providing important information on how L. serricorne targets particular CMMs. The high attractiveness of paeonal at low doses tested here may be exploited further to develop novel monitoring and control tools (e.g., lure-and-kill strategies) against this important stored product pest.