Cabbage loopers disable canal-borne defenses of hostplants by cutting trenches across leaves before feeding. An alkaloid, lobeline, applied to looper mouthparts stimulates trenching even on plants lacking secretory canals. Lobeline acts as an antagonist of nicotinic acetylcholine receptors; it occurs naturally in leaves of cardinal flower, Lobelia cardinalis (Campanulaceae). First and third instar cabbage loopers sleeved on L. cardinalis fail to develop even though the third instar larvae attempt to trench. Final instar larvae cut trenches readily, but suffer low survivorship. These results document that trenching ability does not guarantee effective feeding. Trenching assays offer a novel approach for identifying defensive plant compounds with insecticidal properties and potential applications in agriculture or medicine.
Species 1: Lepidoptera Noctuidae Trichoplusia ni (cabbage looper)
Species 2: Asterales Campanulaceae Lobelia cardinalis (cardinal flower)
Keywords: lobeline, neurotoxin
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