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About this episode

William Haines presenting. For at least the last century, koa forests on the islands of Maui and Hawaii have been defoliated by caterpillars of the endemic moth Scotorythra paludicola. These outbreaks are apparently natural phenomena, occurring relatively infrequently and causing low tree mortality. However, there have been two major outbreaks on East Maui in the past 6 years (2003-2004 and 2008-2009), defoliating about 16km2 of koa forest in Kipahulu Valley and Makawao Forest Reserve, and resource managers are concerned that defoliation in today's environment allows understory weeds to establish, and?that more frequent outbreaks may cause higher tree stress or mortality. Triggers for outbreaks are unknown, as are the likely effects of climate change on their frequency. Here we report on monitoring of S. paludicola in Makawao Forest Reserve, and possible factors influencing populations. To examine abiotic factors, we analyzed the predictive effect of temperature and rainfall on outbreak occurrence during the past 100 years. We did not find a significant effect of either, although our analyses were limited by a small number of outbreaks reported in the literature, and there is some evidence that low rainfall might precede outbreaks. To monitor populations of caterpillars and parasitoids, we collected and reared over 1000 caterpillars in recent years. All parasitoids reared from caterpillars were non-native, although native parasitoids have been documented from S. paludicola in the past. Long term, quantitative monitoring of moth populations, local climate, parasitism, and other factors will be necessary to get to the bottom of these outbreaks.

• Release Date

  Aug 6, 2009

• Runtime

  20:23