An effective cold storage method for stockpiling Halyomorpha halys eggs for field surveys and laboratory rearing of Trissolcus japonicus

Abstract

An effective stockpiling method for egg masses of the invasive brown marmorated stink bug (Halyomorpha halys [St[a]l]; Hemiptera: Pentatomidae) would be useful for rearing and field studies of its egg parasitoid Trissolcus japonicus (Ashmead) (Hymenoptera: Scelionidae). The current method of stockpiling H. halys egg masses at sub-zero temperatures has lethal and sublethal fitness consequences for T. japonicus. We show that parasitoid emergence from egg masses refrigerated at 8{degrees}C for up to two months before parasitism is higher than from frozen egg masses and usually has minimal or no sublethal fitness effects (sex ratio, development time, activity, fecundity, longevity, and weight) on emerging T. japonicus. Only after two months of host egg refrigeration did the emergence of T. japonicus begin to decrease significantly (by 9.6% relative to untreated viable egg masses), whereas egg masses previously frozen at -80{degrees}C had a 58.8% reduction in parasitoid emergence after 14 days of storage. Refrigerated egg masses that were subsequently exposed to average field temperatures (warm: 22.9{degrees}C; cool: 13.2{degrees}C) were still suitable for T. japonicus parasitism after 7 days, while viable egg masses exposed to warm temperatures for 7 days before parasitism had 24.1% lower parasitoid emergence. Our results demonstrate that refrigeration at 8{degrees}C, while resulting in complete mortality of H. halys embryos after 10 days, are more suitable for T. japonicus parasitism than those stored at sub-zero temperatures. The quantity and quality of H. halys eggs that can be stockpiled with this method could facilitate T. japonicus laboratory colony maintenance, field monitoring, and releases.