Fig 4. Feeding deterrence of the fifth instar Helicoverpa armigera larvae to coumarin by contact chemoreception.

(A) Two-choice feeding assays with cowpea leaf discs: the feeding area of coumarin-treated discs (grey bars) and control discs (white bars) were measured (n = 19–20). (B) Modified two-choice feeding assays with ‘sandwich’ leaf discs: in the contact two-choice feeding assay, coumarin or control discs were painted on the upper leaf discs (n = 25); in the non-contact feeding assay, coumarin or control discs were painted on the lower leaf discs that prevented larvae from feeding (n = 24); the feeding area of the consumed upper leaf discs was measured. Feeding deterrence index (D.I.) = (consumed areas of the control discs—consumed areas of the treated discs) / (consumed areas of the control discs + consumed areas of the treated discs). Data are mean ± SEM. *** and ns indicate significant difference (p < 0.001) and no significant difference (p > 0.05), respectively (two-tailed paired samples t-test).