We discovered an undescribed species of Leiophron parasitizing mirid nymphs in Argentina and Paraguay; this euphorine braconid is described as Leiophron argentinensis Shaw n. sp. Wasps were reared from several mirid species collected on numerous host plants, but most parasitoids (>85%) were reared from Taylorilygus apicalis (Fieber), which was the most abundant mirid. Parasitism rates ranged from 0 to 37% and averaged ≈7% for the entire study. Excluding samples where parasitism was not observed, parasitism rates averaged ≈9%. Parasitism levels were highest in the summer. Host plant species significantly influenced parasitism levels of T. apicalis; nymphs on Conyza spp. suffered ≈16% parasitism, significantly more than nymphs on other host plants. L. argentinensis was collected throughout the study area (≈22–35° S), although the entire geographic range of this species is not yet known. We observed a transition from a male-biased sex ratio in the summer to a female-biased sex ratio in the fall. L. argentinensis has several generations per year and apparently produces some diapausing individuals in each generation. The incidence of diapause was lowest in the summer (≈40%). In laboratory trials, L. argentinensis readily parasitized Lygus lineolaris (Palisot de Beauvois) and Lygus hesperus Knight, suggesting that L. argentinensis has potential as a biological control agent for these pests in the United States.
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Vol. 96 • No. 6