Caterpillars are primary consumers that exert strong selective pressures on host plants. Plants, in turn, possess a range of defenses against herbivores. Leaf trichomes, for example, can act mechanically or chemically by damaging the insect's cuticle, restricting movement, disrupting attachment, or exposing insects to deterrent or toxic compounds. These defenses are especially challenging for neonate caterpillars, whose small size, soft bodies, and limited physiological capacity increase their vulnerability. To cope with these challenges, neonates have evolved multiple, non-exclusive strategies to evade or mitigate plant defenses. Here, we tested whether neonate caterpillars selected specific leaf sites in response to the distribution of non-glandular and glandular trichomes. We tested this with neonates of the masked birch caterpillar, Drepana arcuata Walker, 1855 (Drepanidae) on paper birch, Betula papyrifera Marshall (Betulaceae), leaves. We first quantified where neonate caterpillars established their shelter across leaf surfaces (adaxial vs. abaxial) and regions (base, middle, outer edge, and tip). Our findings showed that neonate establishment was non-random. Larvae more frequently established on the adaxial surface, even when initially placed abaxially, and predominantly near the leaf margins (base, outer edge, and tip) rather than in the middle. We then characterized trichome densities and tested whether they were associated with the distribution of established shelters. Both trichome types were non-uniformly distributed on paper birch leaves and negatively correlated with the number of established larvae, indicating that larvae preferentially selected sites with lower trichome densities. We also examined whether established larvae actively avoid feeding on trichomes. Larvae selectively bypassed glandular trichomes while skeletonizing leaf tissue. These results show that neonate D. arcuata selectively choose specific sites on leaves and that they avoid both non-glandular and glandular trichomes, suggesting that variation in leaf trichomes is an important determinant of micro-habitat selection in neonate caterpillars.
ABSTRACT This study focuses on Eumerus obliquus (Fabricius, 1805) (Diptera: Syrphidae) and aims to enhance the understanding of the life history of the genus Eumerus through an analysis of its life cycle and population parameters. The research was conducted using the ‘age‐stage, two‐sex life table’ approach. Several key biological and demographic parameters were obtained, enabling the estimation of population dynamics under controlled artificial rearing conditions. The results revealed a positive population growth trend (e.g., intrinsic rate of increase: 0.08 day −1 ). The larval stage was identified as the most critical phase in the captive rearing process employed, exhibiting the highest mortality. On average, preadult development lasted 32.5 days, and adult longevity was 22.31 days, with no differences shown between both sexes. Mean fecundity was 258.2 eggs per female, with a maximum of 135 eggs laid in a single day and 885 over a female's lifetime. Notably, only one female failed to oviposit during the experiment. The preoviposition period (APOP) was 4.4 days. Overall, E. obliquus responded favourably to the rearing protocol, and the results obtained with the age‐stage, two‐sex life table method are consistent with the species' expansive character, as it continues to extend its distribution range globally.
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.
