Review of the Nearctic Species of Leiophron and Peristenus (Hymenoptera: Braconidae: Euphorinae) Parasitizing Lygus (Hemiptera: Miridae: Mirini)

Plant bugs belonging to the genus Lygus Hahn (Hemiptera: Miridae) are important pests of a wide variety of North American crops. Efforts to use biological control as one strategy in an integrated pest management approach have been impeded by a poor understanding of the endoparasitoids, particularly species of the genera Leiophron Nees and Peristenus Foerster (Hymenoptera: Braconidae) many of which parasitize the nymphal stages of Lygus, among other Miridae. The taxonomy of Leiophron and Peristenus species associated with agricultural habitats is reviewed based on reared material contributed by numerous researchers. Sixteen species of the two genera were found parasitizing Lygus nymphs, including the following eight species described as new, Leiophron australis Goulet, L. simoni Goulet, Peristenus braunae Goulet, P. broadbenti Goulet, P. carcamoi Goulet, P. dayi Goulet, P. gillespiei Goulet and P. otaniae Goulet. The species are differentiated in a key, described and illustrated. Two names are newly placed in synonymy, L. trigonotylidis Loan, 1974 under Leiophron lygivorus (Loan 1970) and Brachistes nocturnus Viereck, 1905 under P. mellipes (Cresson 1872). Euphorus mellipes Cresson is removed from synonymy with P. pallipes (Curtis). Most of the endoparasitoid species are known to be associated only with Lygus spp. and appear to be distinct in their distribution and their biology. Analysis of the endoparasitoid complex in southern Quebec shows that of the six species that occur in alfalfa and hay fields, four species use Lygus lineolaris (Palisot) as the main host. The introduced Peristenus digoneutis Loan has recently established in southern Quebec and although its numbers have increased substantially it has not yet had an evident impact on reducing L. lineolaris population levels.