Regulation of Underground Insect Herbivores: Subterranean Trophic Cascades?

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9508673 STRONG This research focuses on a below-ground trophic cascade involving a root-feeding moth caterpillar, a bush lupine, a soil-dwelling entomopathogenic nematode, and predators on this nematode. It is the nematode predators that initiate this cascade. These predators are primarily the nematophagous fungi impertecti, which are speciose and abundant in soils. The trophic interactions are constructed as follows: Dead lupine killed by caterpillars are substrates for mushrooms that are putatively the reproductive stages of the nematophages. With opposite potential effect, leaves bearing copious alkaloids that are potent fungicides accumulate in thick blankets on the soil habitat of the nematophagous stages of the fungi. Neither the caterpillar, which consumes only wood low in alkaloid, nor the nematode appear to be affected by these alkaloids. The caterpillars are widely dispersed among lupine patches, yet their numbers are negatively correlated with nematode abundance. The nematodes suffer frequent local extinctions and are present only in areas where lupines flourish. However, where caterpillar densities are high, both lupine litter and the nematode-eating fungi are abundant. In these areas, there are a few nematodes. Soils are among the most poorly known habitats of life on earth. Underground insect herbivores, which are diverse, injurious to plants, and influential in ecosystems, have been studied to a degree in agriculture systems, but have had only had cursory treatment by ecologists. Population regulation of underground insect herbivores has been almost totally ignored by agriculturalists and ecologists alike. While underground insects are drawn from familiar above-ground groups, their natural enemies in the soil are distinctive. This research has clear linkages to understanding factors that regulate populations of below-ground herbivores in natural and agricultural communities.