Extreme weather events dramatically impact populations of individual insect species but the consequences of such events for entire insect communities are not well documented. We present evidence that mid spring frosts and summer drought negatively affect the community of insects found on Missouri oaks (Quercus alba and Q. velutina), amounting to a 23-186 fold decrease depending on the oak species, insect body size and feeding guild, and the specific weather event. Depending on the event, spring faunas required 1-5 years and summer faunas 1-4 years following spring frosts to reach pre-event levels. The impact of summer drought on leaf tying caterpillars also lasted over an extended period of time; it was 5 years before numbers of leaf ties reached pre-drought levels. Smaller-bodied species of leaf tying Lepidoptera took longer to recover than largerbodied species following the drought. Overall, we found no evidence for a general decline in abundance, even a modest one, during the 20 years of study of faunas on oak trees in southeastern Missouri. However, the risk of mid-season frost damage to trees is expected to increase with predicted earlier onset of spring. Similarly, the effects of drought reported here are likely to increase with time, as the climate in the Midwest U.S. is only expected to become warmer and drier during the summer months. Understanding the impact of such weather events on insect communities influences our ability to predict how habitat and landscape management, or lack thereof, will influence future patterns of insect abundance and diversity.

Elevated atmospheric CO2 is known to affect plant-insect herbivore interactions. Elevated CO2 causes leaf nitrogen to decrease, the ostensible cause of herbivore compensatory feeding. CO2 may also affect herbivore consumption by altering chemical defenses via changes in plant hormones. We considered the effects of elevated CO2, in conjunction with soil fertility and damage (simulated herbivory), on glucosinolate concentrations of mustard (Brassica nigra) and collard (B. oleracea var. acephala) and the effects of leaf nitrogen and glucosinolate groups on specialist Pieris rapae consumption. Elevated CO2 affected B. oleracea but not B. nigra glucosinolates; responses to soil fertility and damage were also species-specific. Soil fertility and damage also affected B. oleracea glucosinolates differently under elevated CO2. Glucosinolates did not affect P. rapae consumption at either CO2 concentration in B. nigra, but had CO2-specific effects on consumption in B. oleracea. At ambient CO2, leaf nitrogen had strong effects on glucosinolate concentrations and P. rapae consumption but only gluconasturtiin was a feeding stimulant. At elevated CO2, direct effects of leaf nitrogen were weaker, but glucosinolates had stronger effects on consumption. Gluconasturtiin and aliphatic glucosinolates were feeding stimulants and indole glucosinolates were feeding deterrents. These results do not support the compensatory feeding hypothesis as the sole driver of changes in P. rapae consumption under elevated CO2. Support for hormone-mediated CO2 response (HMCR) was mixed; it explained few treatment effects on constitutive or induced glucosinolates, but did explain patterns in SEMs. Further, the novel feeding deterrent effect of indole glucosinolates under elevated CO2 in B. oleracae underscores the importance of defensive chemistry in CO2 response. We speculate that P. rapae indole glucosinolate detoxification mechanisms may have been overwhelmed under elevated CO2 forcing slowed consumption. Specialists may have to contend with hosts with poorer nutritional quality and more effective chemical defenses under elevated CO2.