Effect of forest microhabitat and larval stage on overwintering survival, development, and phenology of Spathius galinae (Hymenoptera: Braconidae), biological control agent of emerald ash borer, Agrilus planipennis (Coleoptera: Buprestidae)

Authors

  • Adam Scherr USDA-ARS Beneficial Insect Introduction Research Unit, 501 South Chapel Street, Newark, Delaware 19713, USA
  • Nicole Quinn USDA-ARS Beneficial Insect Introduction Research Unit, 501 South Chapel Street, Newark, Delaware 19713, USA
  • Douglas Tallamy University of Delaware, Department of Entomology and Wildlife Ecology, Newark, 531 South College Avenue, Newark, Delaware 19716, USA
  • Jian Duan USDA-ARS Beneficial Insect Introduction Research Unit, 501 South Chapel Street, Newark, Delaware 19713, USA

Abstract

Spathius galinae Belokobylskij (Hymenoptera: Braconidae) is among several parasitoids introduced as classical biocontrol agents for control of the invasive emerald ash borer, Agrilus planipennis Fairmaire (Coleoptera: Buprestidae), in the US. However, the successful establishment of this parasitoid and its efficacy in suppressing emerald ash borer vary among the release sites and regions. We hypothesize that forest microhabitats and parasitoid overwintering life stages affect parasitoid overwintering survival, development, and emergence phenology of adults in the spring. To test this, we placed logs containing 3 different larval stages of S. galinae (early instar larva, late instar larva, and cocoon) in ventilated jars in 2 distinct microhabitat sites, i.e., urban forest and mature natural forest. These were deployed in late fall of 2020 and remained in the field through winter. The emergence of adult parasitoids was recorded in spring through summer of 2021. Parasitoids in the warmer urban site emerged more quickly, emerging 12 d earlier than parasitoids in the cooler mature forest site. None of the S. galinae deployed as early instar larvae diapaused in either urban or forest sites. In both habitats, 27.1 to 32.1% of late instar larvae diapaused. Across overwintering larval stages, the median time of S. galinae emergence was about 24 d in the urban microhabitat, significantly shorter than that (36 d) observed in the mature forest microhabitat. Our findings suggest that environmental factors profoundly affect S. galinae phenology, and consequently emerald ash borer biological control.

 

Resumen

Spathius galinae Belokobylskij (Hymenoptera: Braconidae) se encuentra entre varios parasitoides introducidos como agentes de biocontrol clásico para el control del barrenador esmeralda del fresno invasivo, Agrilus planipennis Fairmaire (Coleoptera: Buprestidae), en los EE. UU. Sin embargo, el establecimiento exitoso de este parasitoide y su eficacia para suprimir el barrenador esmeralda del fresno varían entre los sitios y regiones de liberación. Nuestra hipótesis es que los microhábitats del bosque y los estadios de vida de hibernación del parasitoide afectan la sobrevivencia, el desarrollo y la fenología de emergencia de los adultos en la primavera. Para probar esto, colocamos troncos que contenían 3 estadios larvales diferentes de S. galinae (larva de estadio temprano, larva de estadio tardío y capullo) en frascos ventilados en dos sitios de microhábitat distintos, un bosque urbano y un bosque natural maduro. Estos se desplegaron a fines del otoño del 2020 y permanecieron en el campo durante el invierno. Se registró la aparición de parasitoides adultos desde la primavera hasta el verano del 2021. Los parasitoides en el sitio urbano más cálido emergieron más rápidamente, emergiendo 12 días antes que los parasitoides en el sitio de bosque maduro más frío. Ninguno de los S. galinae se desplegó como larvas de estadio temprano en diapausa en sitios urbanos o forestales. En ambos hábitats, entre el 27,1 y el 32,1% de las larvas de estadio tardío entraron en diapausa. A lo largo de los estadios larvales de hibernación, la media del tiempo de emergencia de S. galinae fue de aproximadamente 24 días en el microhábitat urbano, significativamente más corto que el (36 días) observado en el microhábitat de bosque maduro. Nuestros hallazgos sugieren que los factores ambientales afectan profundamente la fenología de S. galinae y, en consecuencia, el control biológico del barrenador esmeralda del fresno.

Key Words: biological control; parasitoid; invasive species

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Author Biography

Nicole Quinn, USDA-ARS Beneficial Insect Introduction Research Unit, 501 South Chapel Street, Newark, Delaware 19713, USA

assistant professor, entomology, biological control, Entomology and Nematology Department, UF/IFAS Research and Education Center, Fort Pierce, FL

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Published

2023-07-17

Issue

Vol. 106, No. 2 (June 2023)

Section

Research Papers

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