How will eastern tent caterpillars respond to climate change?

Background/Question/Methods

In this study we integrate phenology observations with lab manipulations to understand the seasonality of eastern tent caterpillars (Malacosoma americanum, ETC hereafter). Tent caterpillar populations fluctuate from year to year, alternating between outbreaks and low densities. Early spring synchrony between caterpillar hatching and host plant budburst could be a factor affecting ETC populations, which would grow when in synchrony and collapse under asynchrony. Global climate change has the potential to affect ETC population dynamics because heat accumulation is the main hatching cue for this species. However, Fitzgerald (1995) suggested that volatiles emitted during plant budburst could induce caterpillar hatching when foliage is present. Here we tested that hypothesis and also investigated if warmer winter and spring conditions affect the ability of ETC to deal with asynchrony. Specifically, we i) recorded the spring phenology of wild ETC colonies and their food plants, and did laboratory assays to ii) determine if caterpillars are using plant volatiles to fine tune their hatching with budburst, iii) evaluate how winter and spring temperatures affect ETC hatching patterns and their ability to endure starvation, and iv) we investigated if larval early starvation has long term effects on two fitness correlates: development time and pupal mass.

Results/Conclusions

Caterpillars from Rock Creek Park, DC hatched before black cherry bud burst, but in synchrony with bud enlargement, when edible plant tissue was present. Warm winter temperatures resulted in advanced hatching time, regardless of spring temperature conditions. Our results did not support the hypothesis that ETC use chemical foliage cues to synchronize their hatching with foliage availability. We found that ETC can survive for almost two weeks without food and a difference of 4°C in post-hatch day temperature did not affect their ability to endure starvation in the lab. In contrast, for colonies overwintering at ambient conditions, experiencing a spring regime 4°C higher significantly decreased their ability to endure starvation. We found population-level variation in starvation endurance: colonies from GA survived for longer periods of time than colonies from the DC area. Finally, early starvation had a severe effect on hatchling survival, with mortality rates increasing linearly with starvation period length. Interestingly, those individuals that survived did not show negative effects in development time nor on pupal mass, regardless of the length of the starvation period, suggesting a strong compensatory feeding ability.