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B430: How do specialist caterpillars cope with stiff and sharp plant trichomes? (Lead Supervisor: Walter Federle, Zoology)

Supervisors: Walter Federle (Zoology) and Chris Jiggins (Zoology

Importance of the area of research:

Plants can defend themselves against herbivory not only chemically, but also by physical means. Physical plant defences include trichomes which can deter insects by forming dense carpets that make walking and feeding difficult, or by being sticky and entangling insect visitors. Some defensive plant trichomes are stiff and sharp spines/hooks which can injure or kill insects mechanically by piercing their outer cuticle or gut if the trichomes are ingested [1]. However, certain specialist herbivores are able to move and even feed on host plants covered in such trichomes. The detailed mechanisms underlying the plants' physical defence and the caterpillars' resistance are still unknown. Uncovering such mechanisms has the potential to inspire new types of pest control strategies.

Project summary:

This project aims to clarify adaptations of Heliconius charithonia caterpillars to move and feed on Passiflora adenopoda and P. lobata vines, which are covered in stiff and sharp trichomes [2]. First, we will quantify the mechanical properties of the plants' hooked trichomes to estimate piercing stress levels. Second, we will compare how specialist and non-specialist Heliconius caterpillars interact with the hooked trichomes. To identify behavioural adaptations, we will film the caterpillar's body, leg and proleg movements and their attachment on the leaf surface. A small-scale penetrometer will be developed to measure the stresses required to pierce the cuticle and gut, and friction forces of the cuticle will be measured. The project will also focus on underlying genetic mechanisms of caterpillar resistance by studying the transcriptome of midgut cells in Heliconius via RNA-seq.

What the student will do:

The student will use a sensitive fibre-optic force transducer setup to measure the compliance and breaking strength of the plants' hooked trichomes. The sharpness of the trichomes will be quantified using SEM. The locomotion of specialist and non-specialist Heliconius caterpillars on leaves with hooked trichomes will be recorded. Piercing forces and stresses will be estimated from the deflection of trichomes. To measure the stresses required for piercing the cuticle of specialist and generalist caterpillars, the student will develop a small-scale penetrometer. The frictional resistance of spherical contacts on the cuticle surface of different caterpillars will be measured. The detailed internal and surface morphology of the caterpillars' cuticle will be studied using light and electron microscopy. The student will perform RNA-seq transcriptomics of Heliconius midgut cells, comparing specialist Heliconius feeding on Passiflora species with and without trichomes, and generalist Heliconius species on trichome-free Passiflora. Upregulation of genes mediating repair of the midgut epithelium in response to chemical plant defences has been previously shown in other caterpillars [3].

Please contact the lead supervisor directly for further information relating to what the successful applicant will be expected to do, training to be provided, and any specific educational background requirements.

References:

1. Pillemer E, and Tingey W. 1976. Hooked trichomes: A physical plant barrier to a major agricultural pest. Science 193: 482-484.

2. Cardoso MZ. 2008. Herbivore handling of a plant's trichome: the case of Heliconius charithonia (L.) (Lepidoptera: Nymphalidae) and Passiflora lobata (Killip) Hutch. (Passifloraceae). Neotropical Entomology 37: 247-252.

3. Fescemyer HW, Sandoya GV, Gill TA, Ozkan S, Marden JH, and Luthe DS. 2013. Maize toxin degrades peritrophic matrix proteins and stimulates compensatory transcriptome responses in fall armyworm midgut. Insect Biochem. Mol. Biol. 43: 280-291.

Follow this link to find out about applying for this project.

Other projects available from the Lead Supervisor can be viewed here.

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