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

item WATT, TIMOTHY - University Of Delaware
item Duan, Jian
item TALLAMY, DOUGLAS - University Of Delaware
item HOUGH-GOLDSTEIN, JUDY - University Of Delaware
item ILVENTO , THOMAS - University Of Delaware
item YUE, XIN - University Of Delaware
item REN, HUI - University Of Delaware

Submitted to: Biological Control
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 1/28/2016
Publication Date: 1/28/2016
Citation: Watt, T.J., Duan, J.J., Tallamy, D.W., Hough-Goldstein, J., Ilvento , T.W., Yue, X., Ren, H. 2016. Reproductive and developmental biology of the emerald ash borer parasitoid Spathius galinae (Hymenoptera: Braconidae) as affected by temperature. Biological Control. 96:1–7.

Interpretive Summary: The stingless, parasitic wasp (Spathius galinae) is a newly discovered natural enemy of the invasive emerald ash borer (Agrilus plannipennis) that has killed tens of millions of North American ash trees since it was discovered in 2002 in the U.S. This natural enemy has been recently approved for environmental releases in the U.S. for biological control of the invasive emerald ash borer. To better understand its biology and improve outcomes of mass-rearing, scientists from USDA Agricultural Research Service and University of Delaware determined the optimal ambient temperature for immature development and adult longevity and fecundity. Results from our study show that when they are maintained at a range of temperatures from 15 to 35°C for their lifetimes, the female wasps have the highest net reproductive rate, greatest longevity and fecundity at 25oC. These findings will significantly contribute to the development of efficient rearing protocols for mass production of this natural enemy for field releases against the invasive emerald ash borer.

Technical Abstract: 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, has been approved for environmental release in the United States. To better understand its reproductive and developmental biology, and to improve outcomes of mass-rearing, we investigated the effects of temperature (15, 20, 25, 30, and 35°C) on immature development time and sex ratio, as well as adult pre-oviposition period, fecundity and survivorship. Results show that at 15°C S. galinae develops to 5th instar larvae (cocoons) and enter diapause, while at 35°C parasitoid eggs desiccate and do not hatch. Between 20 and 30°C development time is inversely associated with temperature, with adult emergence occurring ˜38, 32, and 25 d after oviposition for 20, 25, and 30°C, respectively, and progeny sex ratio is not affected by temperature. When newly (= 24 h-old) emerged female parasitoids are provided larval hosts throughout their lifetimes, parasitism occurs at all temperatures except 35°C, although parasitism rates are highest (35%), as is lifetime fertility (43 progeny/female), when females live at 25°C. Survival is inversely associated with temperature, with ovipositing females held at 15°C living for >60 d, while females held at 35°C live for <10 d. Life table analyses show S. galinae has the highest net reproductive rate (R0=25.7) and greatest capacity for increase (rc=0.09) when female parasitoids are maintained at 25°C for their lifetimes, suggesting this is the optimal temperature for rearing S. galinae.