Are Basic Substances a Key to Sustainable Pest and Disease Management in Agriculture? An Open Field Perspective.

Pathogens and pests constantly challenge food security and safety worldwide. The use of plant protection products to manage them raises concerns related to human health, the environment, and economic costs. Basic substances are active, non-toxic compounds that are not predominantly used as plant protection products but hold potential in crop protection. Basic substances' attention is rising due to their safety and cost-effectiveness. However, data on their protection levels in crop protection strategies are lacking. In this review, we critically analyzed the literature concerning the field application of known and potential basic substances for managing diseases and pests, investigating their efficacy and potential integration into plant protection programs. Case studies related to grapevine, potato, and fruit protection from pre- and post-harvest diseases and pests were considered. In specific cases, basic substances and chitosan in particular, could complement or even substitute plant protection products, either chemicals or biologicals, but their efficacy varied greatly according to various factors, including the origin of the substance, the crop, the pathogen or pest, and the timing and method of application. Therefore, a careful evaluation of the field application is needed to promote the successful use of basic substances in sustainable pest management strategies in specific contexts.

Acceptance and utilization efficiency of a purple durum wheat genotype by Sitophilus granarius (L.).

The granary weevil (Sitophilus granarius L.) is a major primary pest of stored cereals throughout the world. Among the major classes of plant secondary metabolites, flavonoids can affect insect feeding behaviour and their growth rate. In this study, the susceptibility of an anthocyanin-rich purple durum wheat genotype (T1303) to the granary weevil was evaluated in comparison with two yellow durum (Ofanto) and bread (Mec) wheat varieties. The feeding response and food utilisation efficiency by adult insects was also investigated by calculating nutritional indices in whole flour disk bioassays. Different levels of susceptibility to granary weevil emerged among genotypes tested. The mean food consumption by an insect, F1 progeny, and female parental offspring calculated for the T1303 genotype were significantly lower than those of yellow kernel wheat varieties. Moreover, T1303 genotype induced deterrence in the adult insects as demonstrated by the positive values of the food deterrence index. Besides, relative grow rate and efficiency conversion of ingested food indices were negative for T1303 and positive for both yellow wheat varieties indicating respectively a decrease and an increase of insect body weight during the bioassays. Finally, a higher mortality rate was recorded for insects fed on T1303 flour disks compared to disks obtained from yellow wheat varieties. These results provide evidence for the antifeedant and toxic effects of anthocyanins present in the T1303 pericarp against the granary weevil. Overall, this study contributes new insights into the mechanisms of host acceptance and food utilization by S. granarius and would be useful to identify antifeedant flavonoids as well as to develop varietal resistance-based strategies against this pest.

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.

Olfactory Response of the Spotted Asparagus Beetle, Crioceris duodecimpunctata (L.) to Host Plant Volatiles.

The spotted asparagus beetle, Crioceris duodecimpunctata (L.) is an invasive host-specific pest of asparagus cultivations. To contribute to the understanding of the role of plant volatiles in host-finding by this species, behavioural and electrophysiological tests were carried out. Y-tube olfactometer bioassays, testing intact or mechanically-damaged cladophylls vs. clean air, revealed sexually-dimorphic responses with males being the only sex attracted to both plant materials. Electroantennographic (EAG) assays showed that antennae of both sexes can perceive a wide range of asparagus volatiles. Male and female EAG profiles were almost similar and (Z)-3-hexen-1-ol was by far the most EAG-active compound. (E)-2-hexenal, (±)-linalool, and 3-heptanone elicited the strongest EAG amplitude within the corresponding chemical groups. Eight of the most EAG-active compounds elicited dose-dependent responses indicating the sensitivity of male and female olfactory systems to changes in stimulus concentration. In a Y-tube olfactometer bioassay, (Z)-3-hexen-1-ol at the doses of 1, 10, and 50 µg did not elicit female attraction whereas a significant attraction at the 10 µg dose and a repellent effect at the 50 µg dose was induced in males. Sexual dimorphism of male behavioural response to host plant volatiles is discussed. This study provides a basis for future investigations that could contribute to the development of semiochemical-based monitoring and management strategies for this pest.

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.