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B431: Silk-based attachment of caterpillars on plant surfaces: biomechanics, and cost-benefit analysis of silk production (Lead Supervisor: Walter Federle, Zoology)

Supervisors: Walter Federle (Zoology) and Paul Brakefield (Zoology

Importance of the area of research:

Lepidoptera are one of the major groups of herbivores worldwide. To feed, their larvae must cling tightly to the surface of host plants, which are often too smooth or slippery for caterpillar attachment devices (thoracic legs and abdominal prolegs) to grip. Many species use an alternative attachment strategy: they spin dense silk carpets onto the surface of their host plants, providing their claws with points to hook on. However, silk is a protein-based secretion and therefore costly to produce for herbivores consuming low-nitrogen diets [1]. The caterpillars' silk production is tightly controlled, and depends on the conditions of the substrate. Although essential for caterpillar herbivory, the costs and benefits of silk-based attachment, its control, and the required adaptations have not been studied.

Research into caterpillar attachment mechanisms and silk production may help identify plant traits preventing insect attachment, with implications for crop protection and insect pest control [2].

Project summary:

This project aims to study (1) the costs and benefits of silk production in caterpillars and (2) the biomechanical adaptations for silk-based grip. ;To quantify the cost of silk production, we will use mass spectroscopy and leaf area scans to measure the amount of nitrogen (N) consumed by caterpillars and the proportion of N incorporated into silk. We will study how the N content of plant and artificial diets affect silk production. 15N-feeding experiments will reveal the extent of N recovery from silk deposited by other caterpillars.

To study how silk affects caterpillar fitness, we will ablate spinnerets to monitor feeding rate and growth compared to control groups.

We will study in detail how caterpillars grip on silk carpets by characterising locomotion, gripping forces, and morphological adaptations; the evolution of traits will be traced by mapping them onto available phylogenies.

What the student will do:

The student will use mass spectroscopy and leaf area scans to quantify the amount of N consumed by Bicyclus anynana caterpillars, and the allocation of N to body tissue, frass and silk. Diet effects on silk production will be tested by feeding with plants of varying N or artificial diets. Silk-laying will be quantified by video-tracking of caterpillar movements.

15N-tracer experiments will study if caterpillars can recover silk spun on leaves by other caterpillars. 15N-fed caterpillars will lay silk carpets on leaves, which will then be offered to unlabelled caterpillars, and the amount of 15N transferred will be quantified.

Ablation of spinnerets will test the effects of silk on caterpillar fitness. Feeding and growth rate when feeding on vertical leaves will be compared with unmanipulated caterpillars, and manipulated caterpillars feeding on horizontal leaves.

The mechanics of how caterpillars grip on silk and relevant adaptations will be studied by force measurements, light and scanning electron microscopy (SEM), and video recordings of locomotion.

The evolution of silk-related traits of a range of selected Lepidoptera will be traced by mapping them onto available phylogenies.

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. Berenbaum MR, Green ES, and Zangerl AR. 1993. Web costs and web defense in the Parsnip Webworm (Lepidoptera: Oecophoridae). Environment. Entomol. 22: 791-795.

2. Whitney HM, and Federle W. 2013. Biomechanics of plant-insect interactions. Curr. Opin. Plant Biol. 16: 105-111.

3. Mortimer B, Holland C, and Vollrath F. 2013. Forced reeling of Bombyx mori silk: separating behavior and processing conditions. Biomacromolecules 14: 3653-3659.

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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