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

• Spathius galinae is an important parasitoid of emerald ash borer in the US.
• Temperature affects its reproductive and developmental biology.
• At 25 °C, net reproductive rate (R0) and intrinsic rate of increase (rm) are highest.
• 25 °C should be used to optimally mass-rear Spathius galinae.
• Seasonal temperatures should be considered when releasing this parasitoid.

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 °C) on immature development time, sex ratio, pre-oviposition period, fecundity and survivorship. Results show that between 20 and 30 °C immature development time was inversely associated with temperature, with adults emerging ≈38, 32, and 25 d after oviposition at 20, 25, and 30 °C, respectively. At 15 °C larvae developed to 5th instars and spun cocoons before development was arrested, while at 35 °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 (⩽24 h-old) emerged female parasitoids were provided larval hosts throughout their lifetimes, adults parasitized at all temperatures except 35 °C, although parasitism rate was highest (35%), as was lifetime fecundity (43 progeny/female), when females lived at 25 °C. Survivorship was inversely associated with temperature, with ovipositing females living for >60 d when maintained at 15 °C, and females held at 35 °C living for <10 d. Life table analyses showed S. galinae had the highest net reproductive rate (R0 = 27.8) and intrinsic rate of increase (rm = 0.29) when female parasitoids were maintained at 25 °C for their lifetimes, suggesting this is the optimal temperature to rear S. galinae.

Demographic parameters, and fitted quadratic lines, for the emerald ash borer parasitoid Spathius galinae, as influenced by constant ambient temperature. R0 (top left) is net reproductive rate; rm (top right) is intrinsic rate of increase; λ (bottom left) is finite rate of increase; and Td (bottom right) is the time required for a population growing at a given rm to double in size.Figure optionsDownload as PowerPoint slide