SQUIRT-GUN DEFENSE IN BURSERA AND THE CHRYSOMELID COUNTERPLOY

I determined the impact of resins canals of Bursera schlechtendalii on the growth and survival of its specialized vein-cutting beetle Blepharida sp. nov. Bursera schlechtendalii produces terpenes stored under pressure in networks of canals that run throughout the cortex of the stem and in the leaves. When a leaf is broken, it releases abundant resins, which may bathe the leaf surface and often form a squirt that travels for up to 150 cm. Plants vary in the proportion of their leaves that release resins after damage. Larvae of the chrysomelid genus Blepharida can inflict substantial damage to plants because they avoid the squirt response by cutting the leaf veins before consuming the leaves. Nevertheless, resins still protect plants against this insect. Both naturally occurring and experimentally placed larvae had higher mortality on highly responsive plants. Young larvae became mired in secretions after rupturing the canals and died. Also, on highly responsive plants larvae spent more time cutting veins and grew more slowly. Thus, while the squirt response of Bursera is not a completely effective defense, it imposes a handling-time cost on larvae, reduces their growth rate, and increases their mortality.