Leaf trichomes affect caterpillar feeding in an instar-specific manner

Abstract

Leaf trichomes play well-established roles in defense against insect herbivores, both as a physical barrier that impedes herbivore movement and by mediating chemical defenses. However, little work has examined how different trichome types influence herbivory by herbivores at different stages of development. We examined whether caterpillar instar and trichome type (glandular or non-glandular) affected the ability of the specialist herbivore caterpillar Manduca sexta to initiate feeding on 11 Solanaceous species exhibiting variation in the density and type of leaf trichomes. Our results suggest that non-glandular trichomes are far more effective than glandular trichomes in deterring the initiation of feeding by first- and second-instar caterpillars. Meanwhile, neither glandular nor non-glandular trichomes significantly affected the ability of third-instar caterpillars to commence feeding. These findings suggest that while non-glandular trichomes deter feeding initiation by early instar caterpillars, the contribution of both trichomes on later instars may depend on effects after feeding initiation.

The Role of Plant-Associated Microbes in Mediating Host-Plant Selection by Insect Herbivores

“…In addition to plant size, herbivores can also recognize physical plant defense structures, which affect host-plant selection. For instance, insect herbivores can recognize and clip plant trichomes to more easily access leaf tissues, although this behavior slows feeding and reduces insect performance [127]. Hence, herbivores may preferentially select plants producing fewer trichomes to increase foraging efficiency.…”

Eating barbed wire: Direct and indirect defensive roles of non‐glandular trichomes

“…Images by Rupesh Kariyat (a-c) and Adeel Mustafa (d). For details, refer Kariyat et al, 2017Kariyat et al, , 2018 In general, the basic outline of plant defense includes (a) first line of defenses, that is, trichomes and spines that delay feeding, (b) feeding induced primary defense signaling with reactive oxygen species and Ca 2+ , (c) phytohormone signaling mediated through jasmonic acid, salicylic acid, ethylene synthesis, (d) production of defense proteins and volatile organic compounds that act as direct or indirect defenses (Howe & Jander, 2008). However, a few recent studies have reported that these non-glandular trichomes are also capable of bioactive compound synthesis, which can assist or enhance plant chemical defenses.…”

Caterpillars Cooperate to Overcome Plant Glandular Trichome Defenses

“…To test whether caterpillars feed collectively, a field survey recorded aggregation by caterpillars throughout development and a lab experiment tested whether caterpillars move toward each other to feed. The lab experiment tested whether glandular trichomes impede feeding by comparing the time budget, latency to begin feeding (Kariyat et al, 2018) and survival of caterpillars on washed and control leaves. The lab experiment also tests whether feeding in the presence of glandular trichomes is socially facilitated by comparing, between leaf treatments, the proportion of feeding events that occurred alone vs. with a neighbor and by counting the number of feeding holes.…”

“…For instance, Helicoverpa armigera (Lepidoptera: Noctuidae) neonates (Simmonds et al, 2004) and Phthorimaea operculella (Lepidoptera: Gelechiinae) larvae (Gurr and McGrath, 2001) are entrapped on glandular trichome exudates of pubescent tomato varieties, and washing leaves with ethanol to remove these secretions decreases P. operculella mortality (Gurr and McGrath, 2002). Similarly, both Helicoverpa zea and Leptinotarsa decemlineata (Coleoptera: Chrysomelidae) feed more and perform better on tomato varieties with fewer glandular trichomes (Tian et al, 2012), and early-instar Manduca sexta neonates initiate feeding faster on trichome-free plants (Kariyat et al, 2018).…”