Simple SummaryThe brown stink bug,Euschistus heros, is a key pest affecting soybean crops in Brazil and other South American countries. Temperature plays a crucial role in insect development and reproduction; however, little is known about temperature onE. heros’ fitness. This study examined the effects of both constant and fluctuating temperatures onE. heros’ biological characteristics across three generations. Development did not occur at constant temperatures of 19 °C and 34 °C, and at 31 °C, there was no reproduction. Development duration was faster at warmer constant temperatures, but fluctuating temperatures decreasedE. heros’ egg viability. This research allowed the development of temperature base and degree day requirements for eachE. herosstage and revealed that about 40% mortality occurs during molting, with the highest mortality between first and second-stage nymphs. Together, these data improve the management ofE. herosand benefit the mass production of egg parasitoids used for its control.AbstractThe brown stink bug,Euschistus heros(Fabricius, 1798) (Hemiptera: Pentatomidae), is one of the most abundant soybean stink bug pests in Brazil. Temperature is a key factor that affects its development and reproduction, and fluctuating temperatures may impact the development and reproduction ofE. herosdifferently from those under constant temperatures. The objective of this study was to evaluate the influence of constant and fluctuating temperature on the biological characteristics ofE. herosin three successive generations. Treatments consisted of six constant temperatures (19 °C, 22 °C, 25 °C, 28 °C, 31 °C and 34 °C) and four fluctuating temperatures (25:21 °C, 28:24 °C, 31:27 °C, and 34:30 °C) evaluated for three successive generations. Second-stage nymphs were evaluated daily, and after they reached the adult stage, they were separated by sex, and the individual weight (mg) and pronotum size (mm) were recorded. After pair formation, eggs were collected to evaluate the pre-oviposition period, total number of eggs, and egg viability. The duration of the nymphal stage was reduced with an increase in both constant and fluctuating temperatures; however, at constant temperatures of 19 °C, 31 °C and 34 °C and fluctuating temperatures of 28:24 °C, there was no reproduction in adults. The base temperature and total degree day requirement for nymphal development were 15.5 °C and 197.4 dd, respectively. Pre-oviposition period (d), number of eggs per female, and viability of eggs (%) were affected by temperature across the generations. The multiple decrement life table analysis revealed that mortality was highest during the molting of the second-stage nymphs. These findings have important implications forE. heros’ laboratory mass-rearing programs and for its management in fields.