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.

Keywords: Glandular trichomes; Manduca sexta; Solanaceae; larval instar; non-glandular trichomes.

Figure 1.

(a) Trichome morphology of S. eleaegnifolium. S. eleaegnifolium produce non-glandular stellate trichomes. Adaxial leaf surface magnified at 12X. (b) Trichome morphology of S. tuberosum. S. tuberosum produce glandular trichomes. Adaxial leaf surface magnified at 12X.

Figure 2.

Time (in seconds) taken by M. sexta caterpillars to commence feeding on 11 Solanaceae species that vary in their trichome type (glandular or non-glandular). Asterisks (*) denote statistical significance at P < 0.05, ** P < 0.01, *** P < 0.001, and **** P < 0.0001.

Figure 3.

Time (in seconds) taken by first-, second-, and third-instar M. sexta caterpillars to commence feeding on 11 Solanaceae species. Asterisks (*) denote statistical significance at P < 0.05, ** P < 0.01, *** P < 0.001, and **** P < 0.0001. Results from pairwise post hoc Tukey comparisons.

Figure 4.

Pairwise comparisons of the effects of Instar X trichome-type interactions on time taken by first-, second-, and third-instar M. sexta caterpillars to commence feeding on 11 Solanaceae species varying in trichome type (glandular or non-glandular). Asterisks (*) denote statistical significance at P < 0.05, ** P < 0.01, *** P < 0.001, and **** P < 0.0001. Results from pairwise post hoc Tukey comparisons.