HOST-RANGE OF GENERALIST CATERPILLARS - TRENCHING PERMITS FEEDING ON PLANTS WITH SECRETORY CANALS

To test if secretory canals limit the host ranges of polyphagous moth larvae, we measured the growth of Trichoplusia ni (cabbage looper) and Spodoptera ornithogalli (yellow-striped armyworm) on plants in nine families, including species with and without secretory canals. Larvae were reared to the final instar on excised leaves of the test plant, weighed, then enclosed in the field on either detached leaves with depressurized canals or intact leaves with undamaged canals. After 24 h, the larvae were reweighed and the leaves were examined for evidence of trenching. For comparison, nine additional species of generalist caterpillars were tested on Lactuca serriola (with latex canals) using the same procedure; five of these species were also tested with Petroselinum crispum, which has resin canals.