Parasitism of frozen Halyomorpha halys eggs by Trissolcus japonicus: Applications for rearing and experimentation

Authors: MCINTOSH, HANNA - University Of Wisconsin; LOWENSTEIN, DAVID - Oregon State University; WIMAN, NIK - Oregon State University; WONG, JESSICA - Oregon State University; Lee, Jana

Submitted to: Biocontrol Science and Technology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 12/11/2018
Publication Date: 1/10/2019
Citation: McIntosh, H., Lowenstein, D., Wiman, N., Wong, J., Lee, J.C. 2019. Parasitism of frozen Halyomorpha halys eggs by Trissolcus japonicus: Applications for rearing and experimentation. Biocontrol Science and Technology. 29(5):477-493. https://doi.org/10.1080/09583157.2019.1566439.
DOI: https://doi.org/10.1080/09583157.2019.1566439

Interpretive Summary: The brown marmorated stink bug is devastating pest to growers and nuisance to homeowners since its introduction to the United States. Researchers are examining the use of a parasitic wasp (Samarai wasp) to destroy stink bug eggs. To release this over a large area, we need efficient ways to mass rear the wasps, but this is constrained by availability of fresh stink bug eggs. Therefore, we compared the parasitism rate, development time, sex ratio, and size of wasps reared on fresh versus frozen, newly-laid (<1 d old) versus variably-aged (0-3 d old collections made on Mondays), and frozen egg masses stored up to four years. Frozen egg masses yielded 56-65% fewer wasps, with a 1-3% decrease in parasitism rate per month stored. Also, newly-laid and Monday egg masses had similar rates of parasitism, sex ratio, and development time. This indicates that egg masses do not need to be collected on a daily basis to be viable for experimentation or rearing. Freezing egg masses for any duration did not affect sex ratio or weight of emerged wasps, but did delay emergence by 5-6 d. Next, frozen egg masses are often placed in the field for a few days to 1 week, but we don't know how long the eggs remain viable for parasitism. Thus, to simulate deployment of sentinel egg masses in the field, we incubated frozen egg masses at 20 °C and 30 °C for 1-9 days before exposing them to wasps and evaluated parasitism trends. Emergence rate of wasps decreased 5-8% per day incubated. Unhatched wasps increased 9% per day incubated, and sex ratio was not impacted. Variably-aged, frozen, and longer-stored egg masses can be used for wasp rearing and experimentation without affecting emerged wasp sex ratio or size within one generation but will have lower parasitism and slower development. Frozen sentinel egg masses are effective for <3-5 d, especially in hot conditions.

Technical Abstract: The brown marmorated stink bug, Halyomorpha halys (Stål), has become a well-known pest to growers and homeowners since its introduction to the United States in 1996. A classical biocontrol program is currently under development using the egg parasitoid Trissolcus japonicus. Widespread implementation of biocontrol will require efficient methods for mass rearing, but is constrained by availability of fresh H. halys egg masses. We compared parasitism rate, development time, sex ratio, and size of wasps reared on fresh versus frozen, newly-laid (<1 d old) versus variably-aged (0-3 d old collections made on Mondays), and frozen egg masses stored up to four years. Frozen egg masses yielded 56-65% fewer wasps, with a 1-3% decrease in parasitism rate per month stored. Parasitism rate, sex ratio, and development time were comparable between newly-laid and variably-aged egg masses. Freezing egg masses for any duration did not affect sex ratio or weight of emerged T. japonicus, but did delay emergence by 5-6 d. To simulate deployment of sentinel egg masses in the field, we incubated frozen egg masses at 20 °C and 30 °C for 1-9 days before exposing them to T. japonicus and evaluated parasitism trends. Emergence rate of T. japonicus decreased 5-8% per day incubated. Unhatched wasps increased 9% per day incubated, and sex ratio was not impacted. Variably-aged, frozen, and longer-stored egg masses can be used for T. japonicus rearing and experimentation without affecting emerged wasp sex ratio or size within one generation but will have lower parasitism and slower development. Frozen sentinel egg masses are effective for <3-5 d, especially in hot conditions.