Valorization of clove (Syzygium aromaticum) by-products as potential stored grain protectants

Clove (Syzygium aromaticum) being a most valuable spice, produce stems and leaves as by-products during processing. This study aimed to valorize these by-products as potential grain protectants against rice weevils since it is a novel approach to reducing the post-harvest loss of rice and minimizing synthetic insecticide usage. The composition of clove stem and leaf essential oils was analyzed using gas chromatography-mass spectrometry. Accordingly, the contact repellent activity and fumigation mortality of essential oils were tested while computing the mortality percentage and LD50 values. The yield of stem essential oil (5.52%) was significantly higher than leaf essential oil (3.92%). Further, stem essential oil with a 100 µL dose showed the highest repellency (100.00 ± 0.00%) and mortality (96.67 ± 3.33%) while 50 and 75 µL doses caused similar mortality (83.30 ± 3.33%) after 5 days. The lowest LD50 (28.06 µL/L) was observed on day 5, indicating the higher toxicity of stem essential oil. Eugenol (73.73 and 82.56%), β-caryophyllene (24.84 and 16.67%), α.-humulene (0.82 and 0.33%), and 1S, CIS-calamenene (0.14 and 0.03%) were detected as the major components responsible for the insecticidal activity of stem and leaf essential oils. Hence, the valorization of clove by-products was successful as potential grain protectants, and clove stem essential oil could be the most effective alternative for rice weevil management.

Five natural compounds of botanical origin as wheat protectants against adults and larvae of Tenebrio molitor L. and Trogoderma granarium Everts

The botanical substances constitute valuable alternatives to synthetic insecticides. In the last decades, numerous substances of natural origin have been tested against stored-product insects, mostly as fumigants or for contact toxicity, while there is limited knowledge on the efficacy of plant secondary metabolites if used as grain protectants. In the present study, we evaluated the lethal activity of 2-undecanone, acetic acid, trans-anethole, furfural, (E)-2-decenal and (E, E)-2,4-decadienal as wheat protectants for the management of larvae and adults of two important storage pests, Tenebrio molitor (Coleoptera: Tenebrionidae) and Trogoderma granarium (Coleoptera: Dermestidae). 2-undecanone caused 98.9% mortality to the exposed T. molitor adults at 1000 μl/kg wheat 7 days post-exposure, while acetic acid and furfural followed providing 94.4% and 92.2% mortality respectively. 2-Undecanone and (E)-2-decenal caused the highest mortalities to T. molitor larvae (i.e., 87.8% and 80.0% respectively) exposed to 1000 μl/kg wheat for 7 days. All T. granarium adults were dead at 1000 μl (E)-2-decenal or acetic acid/kg wheat 5 or 7 days post-exposure respectively. Complete (100%) mortality was assessed for larvae exposed to (E, E)-2,4-decadienal and (E)-2-decenal at 1000 μl/kg wheat after 4 and 6 days respectively. Our findings report for the first time that 2-undecanone, (E)-2-decenal, and (E, E)-2,4-decadienal are effective new candidate control agents of different developmental stages of T. molitor and T. granarium.

Insecticidal effect of diatomaceous earth and pirimiphos-methyl against phosphine-susceptible and phosphine-resistant populations of two stored product beetle species

In the present study, we evaluated the insecticidal efficacy of diatomaceous earth (DE) and pirimiphos-methyl for the control of phosphine-susceptible and phosphine-resistant populations of Tribolium castaneum (Herbst) and Sitophilus oryzae (L.). Insecticides were applied on wheat or rice at two doses: DE was applied at 1000 and 2000 ppm and pirimiphos-methyl at 1 and 5 ppm. Adult mortality was measured after 7, 14, and 21 days of exposure, and progeny production capacity on the treated substrates was evaluated 65 days later. For T. castaneum, we found that DE, at 2000 ppm, was able to provide 100% control of two of the three populations tested, while for the third population mortality reached only 84%. Similarly, there were differences in mortality levels after exposure to DE-treated grains between the two S. oryzae populations tested. At 1 ppm, pirimiphos-methyl was not effective for any of the T. castaneum populations tested, but complete mortality was recorded for all populations at 5 ppm. In general, populations of S. oryzae were more susceptible than those of T. castaneum, for both commodities. Our data indicate that both insecticides can be used with success in phosphine resistance management programs, but there are populations of a given species that may be less susceptible, which constitutes a preliminary screening essential.

Insecticidal effect and impact of fitness of three diatomaceous earths on different maize hybrids for the eco-friendly control of the invasive stored-product pest Prostephanus truncatus (Horn)

Diatomaceous earths (DEs) are able to successfully protect grain commodities from noxious stored-product insect and mite infestations; however, their effectiveness may be moderated by the grain hybrid or variety they are applied to. There is a gap of information on the comparison of the efficacy of different DEs when are applied on different maize hybrids against Prostephanus truncatus (Horn). Therefore, here we tested three commercially available DEs (DEA-P at 75 and 150 ppm, Protect-It at 500 ppm, and PyriSec at 500 ppm) on five different maize hybrids (Calaria, Doxa, Rio Grande, Sisco, and Studio) for the control of P. truncatus adults in terms of mortality (at 7 and 14 days), progeny production, properties of the infested maize hybrids (number and weight of kernels with or without holes, number of holes per kernel) and the adherence level of the tested DEs to the kernels. DEA-P was very effective at 75 ppm while a considerable proportion of the exposed P. truncatus adults was still alive after 14 days of exposure on all maize hybrids treated with 500 ppm of Protect-It or PyriSec, even though it was 3.3 times higher than the maximal application tested dose of DEA-P. Apart from parental mortality, DEA-P was able to reduce P. truncatus progeny production in all hybrids contrary to Protect-It or PyriSec. The adherence ratios were always higher for DEA-P than Protect-It or PyriSec to all maize hybrids. The highest numbers of kernels (or weight of kernels) without holes were noticed after their treatment with DEA-P. Doxa and Sisco performed better than Calaria, Rio Grande, or Studio based on the differences found concerning the numbers of kernels without holes at treatments with DEA-P and Protect-It. Overall, the findings of our study indicate the high potentiality of DEA-P as protectant of different maize hybrids to P. truncatus infestations at low doses, a fact that could help the eco-friendly management of this noxious species in the stored-product environment.