How temperature and humidity affect brown marmorated stink bug (Halyomorpha halys) egg masses and the symbionts deposited there

Many insects share intimate relationships with beneficial microbes, which assist their host with a variety of biological processes. These relationships are well documented in the order Hemiptera, and a gut symbiont in the genus Pantoea has been identified from the midgut crypts of the brown marmorated stink bug Halyomorpha halys. This symbiont is deposited on the egg mass surface by the female after she lays them, and nymphs inoculate themselves by probing the egg mass chorions after hatching. Previous work has determined that deprival of these gut microbes negatively impacts the survival, development, and fecundity of H. halys. This study was designed to determine if abiotic factors can impact symbiont survival on the egg mass and by extension the success with which nymphs can acquire them. Egg masses, on the plants on which they were laid, were exposed to different temperature and humidity combinations within growth chambers (mimicking field conditions across the summer season) until hatch. Each egg mass was removed once nymphs hatched and reared in it’s own individual tray under standard rearing conditions, 25° Celsius and 75% humidity. Nymphs were tracked daily for mortality and development until adulthood. Although some treatments showed no difference in hatch rate between them, egg masses exposed to higher temperatures and lower humidity levels produced fewer adults per egg mass. Adults were killed upon eclosion and stored for analysis, and quantitative PCR was used to compare the amount of symbiont DNA present from the midguts of adults between the treatments.