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Honey bees and other wild bee species including bumble bees have experienced population declines in recent decades. Although many stressors are implicated in bee population declines, much attention has focused on neonicotinoid pesticides, which are widely used and known to be toxic to pollinators. One neonicotinoid, acetamiprid, has been studied very little in bumble bees, despite its use on bumble bee–pollinated crops. We assessed the impacts of acetamiprid to the North American bumble bee Bombus impatiens using the microcolony model. We examined nest growth, development, and subsequent nest productivity as measured by drone production. We found that high concentrations of acetamiprid in pollen (4520 µg/kg) significantly impacted nest growth, development, and, ultimately, reproduction (drone production). We found the no‐observable–adverse effect level to be 45.2 µg/kg. Overall, acetamiprid has the potential to negatively impact reproductive endpoints for B. impatiens. However, effects occurred at concentrations substantially higher than expected environmental concentrations that would be achieved when following label rates. Further work is required to assess the effects of this pesticide on B. impatiens via alternate routes of exposure and on queenright colonies. Environ Toxicol Chem 2020;39:2560–2569. © 2020 SETAC. This article has been contributed to by US Government employees and their work is in the public domain in the USA. [ABSTRACT FROM AUTHOR]

We reared Cloeon dipterum from egg hatch to adult at 10 constant temperatures (12.1–33.5°C) to test 3 hypotheses (thermal equilibrium hypothesis, temperature size rule [TSR], and O2- and capacity-limited thermal tolerance [OCLTT]) that account for variation in life-history traits across thermal gradients. Male and female adult size declined ~67 and 78% and larval development time declined ~88% with warming; chronic survivorship (thermal limit for population growth) was highest from 16.2 to 23.9°C (mean = 85%) and declined to 0 at 33.5°C; thresholds for 0 growth and development were 10.0 and 10.7°C, respectively; peak rate of population increase (r) occurred at 27.8°C; rates of growth and development were maximal at 30°C; fecundity was greatest at 12.1°C; and between 14.3 and 30°C, growth and development rates increased linearly and the number of degree days (>10.7°C) to complete development was nearly constant (mean = 271). Acute survivorship during short-term thermal ramping was 0 at 40°C. Warming temperature caused development rate to increase proportionately faster than growth rate; male and female adult size to decrease as per TSR, with adult females ~5× larger at 12.1 than 31.7°C; adult size to decrease proportionately more for females than males; and fecundity to decrease proportionately more than adult female size. TSR was related to differences in the responses of growth and development rates at temperatures above thresholds rather than to thresholds for growth or development per se. Respirometry suggested that OCLTT is more applicable to acute than chronic thermal limits. Cloeon dipterum appears to have a thermal ‘acclimation zone’ between 14.3 and 30°C where development and growth rates change linearly and degree-day requirements to complete metamorphosis are constant. The optimum temperature is ~27.8°C where r is maximum. We propose 5 hypotheses to explain these patterns. [ABSTRACT FROM AUTHOR]