Reproductive and developmental biology of the emerald ash borer parasitoid Spathius galinae (Hymenoptera: Braconidae) as affected by temperature

Emerald ash borer Agrilus planipennis Fairmaire (Coleoptera: Buprestidae) is an invasive pest of serious concern in North America. To complement ongoing biological control efforts, Spathius galinae Belokobylskij and Strazenac (Hymenoptera: Braconidae), a recently-described specialist parasitoid of emerald ash borer larvae, is being released for the first time in the United States. To better understand its reproductive and developmental biology, and to improve outcomes of mass-rearing, we investigated the effects of constant ambient temperature (15, 20, 25, 30, and 35 degrees C) on immature development time, sex ratio, pre-oviposition period, fecundity and survivorship. Results show that between 20 and 30 degrees C immature development time was inversely associated with temperature, with adults emerging approximate to 38, 32, and 25 d after oviposition at 20, 25, and 30 degrees C, respectively. At 15 degrees C larvae developed to 5th instars and spun cocoons before development was arrested, while at 35 degrees C parasitoid eggs desiccated and did not hatch. Sex ratio of adult progeny that were exposed to different temperatures, from eggs, was not affected. When newly (624 h-old) emerged female parasitoids were provided larval hosts throughout their lifetimes, adults parasitized at all temperatures except 35 degrees C, although parasitism rate was highest (35%), as was lifetime fecundity (43 progeny/female), when females lived at 25 degrees C. Survivorship was inversely associated with temperature, with ovipositing females living for >60 d when maintained at 15 degrees C, and females held at 35 degrees C living for <10 d. Life table analyses showed S. galinae had the highest net reproductive rate (R-0 = 27.8) and intrinsic rate of increase (r(m) = 0.29) when female parasitoids were maintained at 25 degrees C for their lifetimes, suggesting this is the optimal temperature to rear S. galinae. (C) 2016 Elsevier Inc. All rights reserved.