Not all insects are created equal.

Despite insects generally following one of three broad life-cycle strategies, there is a lot of variation in life-history characteristics. This variation largely determines how individual species respond to disturbance, including prescribed fire. The table featured in the slide above includes several important characteristics, most notably the number of generations per year, reproductive output, dispersal ability, and overwintering location.

Examples of tolerance.

The above slide includes a couple examples of tolerant, moderately tolerant, and relatively intolerant species of butterfly to prescribed fire. Examples on the left, the Fiery Skipper (Hylephila phyleus) and Monarch (Danaus plexippus), are among the more tolerant. In both cases these insects are migratory (e.g., overwinter outside of Minnesota), and have two or more generations per year. Dormant and early season fires have little effect on these migratory species because they are not around to be effected. In addition, having two or more generations per year allow populations to more quickly recolonize following disturbance.

Examples in the middle that fall into the moderately tolerant category include the Regal Fritillary (Speyeria idalia) and the Karner Blue (Plebejus melissa samuelis) - both species of conservation concern. The Regal Fritillary has only a single generation per year, but also has a relatively long adult lifespan, good dispersal ability, and the ability to lay hundreds to thousands of eggs. The Karner Blue on the other hand has two generations per year, but produces relatively few eggs and has a relatively short adult lifespan. In both of these cases, their mix of life-history characteristics (some favoring a positive response, some favoring a negative response) make them moderately tolerant to disturbance.

Last, but certainly on the least, are the intolerant species on the right. In this case the Leonard's Skipper (Hesperia leonardus) and the Arogos Skipper (Atrytone arogos). Both of these species have a single generation per year, have a short adult lifespan (week), and overwinter on stems or blades of prairie grasses. Because these species overwinter aboveground on blades of grass, and because they are egg, larva, or pupa for > 11.5 months of the year, they are extremely susceptible to disturbance - even if a dormant season fire. Prescribed burning through occupied sites for these species results in a catastrophic loss of individuals - making a neighboring unaffected source population necessary to sustain these species long term.

Note that the federally endangered Poweshiek Skipperling (Oarisma poweshiek) also overwinters and pupates aboveground.

Take-home Message: Not All Insects Are Created Equal

It is important to pay attention to focal species, and their life-history characteristics, when evaluating scientific publications on insects and fire effects.