Adult attraction and resulting larval mortality of Pieris virginiensis on the novel host garlic mustard (Alliaria petiolata)

Pieris virginiensis is a rare, univoltine butterfly that inhabits Eastern deciduous forests and normally uses Cardamine diphylla (Brassicaceae) as its larval host plant. In areas invaded by the European biennial garlic mustard (Alliaria petiolata; Brassicaceae), P. virginiensis females prefer to oviposit on the novel host.  When P. virginiensis eggs hatch on A. petiolata, caterpillars often die after only a few days.  We investigated how two candidate chemicals, sinigrin and alliarinoside, contributed to P. virginiensis larval mortality.  

Sinigrin is the predominant glucosinolate in A. petiolata. Pieris spp. butterflies use the tactile signals of glucosinolates to decide where to oviposit, and Pieris caterpillars possess a special enzyme, the Nitrile Specifier Protein (NSP), which converts the normally toxic glucosinolates into harmless nitriles. We painted sinigrin onto two different acceptable host plants, C. diphylla and Brassica juncea. We found that sinigrin was not the primary reason for neonatal death, but may serve as a feeding deterrent or obstacle to successful development.

Alliarinoside is a chemical unique to A. petiolata that was identified as a feeding deterrent for a related Pieris spp., P. oleracea by Renwick et al. (2001). We painted alliarinoside onto B. oleracea to test the effects on newly hatched P. virginiensis caterpillars. We found that alliarinoside treatment severely reduced survival of P. virginiensis larvae. Alliarinoside may be the primary driver of P. virginiensis larval mortality on the novel host A. petiolata.