ABSTRACT The commercial value of sweet potato tuber root is adversely affected by damage caused by Diabrotica speciosa , whose larvae create holes in the peel and internal tunnels in the flesh as a result of feeding activity. Traditional assessment methods based on visual scoring are subjective and constrain advances in genetic breeding programs. This study aimed to characterize and propose a quantitative methodology for measuring internal and external damage, based on approximating tuber roots to cylindrical geometry. Eight sweet potato genotypes cultivated under field conditions were evaluated. The methodology involved calculating the surface area and volume of each root modeled as a cylinder. External damage (holes) was quantified as the percentage of damaged surface area, whereas internal damage (galleries) was quantified as the percentage of damaged volume. The results demonstrated that damage is predominantly superficial, with a higher proportion of external damage. Susceptibility differed significantly among genotypes. “Beauregard,” “BRS Anembé,” and “BRS Cuia” exhibited the highest total damage indices (> 0.12%) and were classified as susceptible. In contrast, “BRS Cotinga,” “BRS Rubissol,” and “BRS Brazlândia Roxa” showed the lowest damage levels. The geometric method developed proved to be objective and reproducible, representing a substantial methodological advance for evaluating resistance to subterranean pests.
ABSTRACT Plant mechanical defenses constitute the first line of resistance against herbivorous insects, yet their independent effects on insect physiology and gut microbiota remain poorly understood. In this study, we investigated the individual effects of leaf trichomes and epicuticular wax of Brassica juncea (L.) Czern. on Spodoptera frugiperda (Smith) (Noctuidae: Prodeniini) using integrated nutritional, biochemical, and 16S rRNA amplicon sequencing approaches. Trichomes are known to reduce feeding efficiency and nutrient assimilation, whereas epicuticular wax influences insect attachment and feeding behavior. We hypothesized that these distinct modes of action impose differential metabolic and microbial constraints on herbivores. Larvae fed on leaves with intact trichomes but removed epicuticular wax showed an increased CI, but a decrease in the ECI compared with the control (with both wax and trichomes), suggesting metabolic demands. In contrast, leaves without trichomes showed higher ECD, indicating the dominant mechanical constraint shown by trichomes compared to epicuticular wax. Moreover, increased amylase activity and glucose oxidase activity were found in larvae fed on leaves lacking trichomes and wax, respectively. Trypsin‐inhibitory activity was reduced in larvae under trichome stress, indicating adaptive responses to dietary barriers. 16S rRNA amplicon sequencing showed differences in microbial composition in larvae fed with leaves differing in the presence or absence of trichomes and/or epicuticular wax. Wax‐bearing leaves supported higher microbial diversity, whereas the absence of both defenses resulted in a less diverse microbiome. Moreover, the presence of Enterococcus across treatments confirmed its role as a core microbiome member; however, trichome ingestion may disrupt gut integrity, leading to a decline in core taxa and a simultaneous increase in opportunistic genera such as Pseudomonas . Thus, our study shows that the plant mechanical defenses influence insect performance through coordinated changes in feeding efficiency, physiology, and gut microbiota.
ABSTRACT The provisioning of non‐host food sources, such as nectar, is a key strategy in conservation biological control to enhance the fitness and efficacy of natural enemies. The diamondback moth, Plutella xylostella (L.), a globally significant crucifer pest, is often regulated by a complex of larval parasitoids. However, the role of carbohydrate availability in shaping the longevity of this specific pest–parasitoid system in South America remains unexplored. This study assessed the impact of a 40% w/w 1:1 glucose: fructose sugar solution on the adult longevity of P. xylostella and its four dominant parasitoids in central Argentina: Diadegma leontiniae , Apanteles piceotrichosus , Oomyzus sokolowskii and Siphona sp. The facultative hyperparasitoid Conura pseudofulvovariegata was also evaluated. Survival analyses using Kaplan–Meier curves and Cox proportional hazards models revealed that carbohydrate access significantly increased longevity in all species compared to a water‐only control (starvation condition) (Log‐rank test, p < 0.001 for all). However, the magnitude of the response was species‐specific, with C. pseudofulvovariegata showing the greatest relative benefit and P. xylostella the lowest. Under the sugar solution, C . pseudofulvovariegata achieved an exceptional median longevity of 172 days, significantly outliving all other species (Kruskal–Wallis, p < 0.001). These results demonstrate a shared but unequal dependency on exogenous carbohydrates, with natural enemies—particularly the hyperparasitoid—deriving a disproportionate survivorship advantage. The findings underscore that habitat management providing floral resources can selectively fuel natural enemy populations, potentially improving biological control of P. xylostella by enhancing parasitoid longevity and temporal persistence in the crop environment.
ABSTRACT Pest management in turfgrass is primarily driven by organophosphates, neonicotinoids, pyrethroids, diamides, and insect growth regulators. The impact of these commonly used insecticides on predatory activity is inadequately documented, even though predator densities are widely studied. Predatory activity is quantified by analyzing the type and density of impressions left on the clay models. Thus, the objective was to determine the effects of insecticide on predatory activity by examining impression types and density on clay models in insecticide‐treated turfgrass. The insecticides bifenthrin, acephate + imidacloprid, imidacloprid, chlorantraniliprole, tetraniliprole, methoxyfenozide, and novaluron were applied to bermudagrass, and clay models were deployed over time to assess arthropod activity in two trials. Across trials 1 and 2, insecticides had clear but time‐dependent effects on impressions created by predators. Early significant reductions in total impressions were observed for bifenthrin in trial 1 and for acephate + imidacloprid, chlorantraniliprole, and imidacloprid in trial 2 compared to the water treatment; however, these effects did not differ significantly during the mid‐period. In the later period, significant reductions in total impressions re‐emerged, most consistently with bifenthrin and tetraniliprole, with acephate + imidacloprid also demonstrating reductions in impressions on models in trial 2. Paired marks exhibited similar temporal dynamics, further indicating their sensitivity to treatment effects. In contrast, prick, fragment, and dent impressions were unaffected by insecticide treatments, whereas scratch impressions showed variable responses across treatments, with no consistent pattern.
We investigated how egg cannibalism affects growth, development, reproduction and progeny fitness of aphidophagous coccinellids, viz. Menochilus sexmaculatus (Fabricius) and Hippodamia variegata (Goeze). Egg cannibalism provided immediate benefits to first instars by expediting molting; however, it slowed the development of later instars. The non-cannibal later instars fed on aphid, Aphis craccivora (Koch) developed faster with greater bodyweights and immature survival (%) than the cannibals. Both egg cannibalism and aphid predation, however, did not affect adult emergence (%) with female-biased sex ratio. For reproduction, three subsets were designed, viz. (i) Non-cannibal adults who never ate eggs, (ii) Cannibal-adults who ate eggs only during immature stages and after emergence fed on aphids, and (iii) Cannibal-adults who never ate aphids. Non-cannibal females of both species had shorter pre- and post-oviposition periods with longer oviposition period, fecundity, percent egg-viability and adult longevity. We report that cannibal females of M. sexmaculatus and H. variegata, who never ate aphids, laid 21.90 +/- 4.8 and 13.4 +/- 9.30 eggs, respectively, with viability of 32.30% +/- 5.07% and 29.27% +/- 10.33%, respectively, indicating that females cannibalizing eggs throughout their entire life span can ensure their progeny's subsistence during aphid scarcity. We conclude that egg cannibalism provides instant energy to foraging ladybirds, facilitating their survival and supplementing the development of neonates. Cannibalizing eggs can only ensure complete development to aphidophagous ladybirds in the absence of aphids. Female M. sexmaculatus was more fecund with greater cannibalistic instincts than H. variegata.
