none Feeding leek moths on an artificial diet has shown that dimethyl and dipropyl disulfides and methyl-propyl disulfide found in frass arise from sulfur compounds specific to Allium . The addition of either propyl or methyl disulfide or their precursors to the diet leads to appearance of the three disulfides in the frass. This implies the transformation of the S-propyl moiety to S-methyl and vice versa by an as yet unknown mechanism. Biochemistry; Nutrition; Digestion; Defaecation; Diet; Behaviour; Communication; Chemical signals; Parasites diseases and disorders; Parasites; Insect parasites; Hosts; Insect hosts Acrolepia assectella (Yponomeutidae); Chemical composition; Digestion; Food plant, origins of frass kairomones; Faeces; Frass kairomones; Food plants; Allium porrum (leek); Origins of kairomones in frass; Pheromones; Kairomones in frass, food plant origins; Hymenopteran parasites; Diadromus pulchellus; Host kairomone origins Diadromus pulchellus (Ichneumonidae); Lepidopteran hosts; Acrolepia assectella; Host kairomone origins