In the previous post, I discussed the glue that hornworms place on their eggs. Hornworms lay eggs on plants in the Family Solanaceae (tobacco family) that have sticky leaves. The problem of gluing an insect egg to a sticky leaf is easier to solve than gluing eggs to non-adhesive surfaces. Some plants have waxy coatings that have anti-adhesive properties. The “wax blooms” can prevent insects without special adaptations from gaining traction on a plant, feeding on the plant or laying eggs on the plant.
Asparagus has a waxy surface that deters insects from feeding and colonizing. One insect, the Asparagus Beetle, Crioceris asparagi, has overcome the asparagus waxy defenses to achieve pest status. One adaptation is the ability of the beetles to attach their eggs firmly to the waxy surface. Voit and Gorb* investigated the attachment of the beetle eggs to the waxy surface. The accessory gland of the female produces a mixture (primarily lipids and proteins) that coat the surface of the egg. The mixture spreads over the waxy surface of the plant better than water, which tends to bead. Perhaps the lipid acts as a surfactant or carrier that disrupts the plant wax to help the protein integrate into the plant surface. The “glue” mixture forms a complex with the wax and subsequent wax secretions by the plant reinforce the egg attachment.
Asparagus beetles attach the egg to the plant along its narrow width. Thus the contact between egg surface and plant surface is not maximized. Still, the eggs are tightly glued. A force of over 8000 times the weight of the egg is required to dislodge the egg. This explains why previous attempts to control this pest by dislodging the eggs from the plants have failed. It would be difficult to dislodge the egg without damaging the plant.
Studies of insect glues may lead to improvements in synthetic adhesives for human uses.
*Voit and Gorb, 2009. Egg attachment of the asparagus beetle Crioceris asparagi to the crystalline waxy surface of Asparagus officinalis. Proc. R. Soc. B October 2009.