Lack of susceptibility of soil-inhabiting Platyprepia virginalis caterpillars, a native arctiid, to entomopathogenic nematodes in nature

Abstract

Entomopathogenic nematodes (EPNs) can kill and regulate populations of soil-inhabiting insects, but studies evaluating these interactions in native ecosystems are rare. The objective of this study was to examine the effects of EPNs on a non-agricultural caterpillar, Platyprepia virginalis (Boisduval) (Lepidoptera: Arctiidae), under natural conditions. Platyprepia virginalis caterpillars live in litter on the soil surface feeding beneath bush lupine during summer, autumn, and winter. Initial laboratory assays revealed that the caterpillars were vulnerable to at least two species of EPNs with which they co-occur in the coastal prairie in northern California (USA). In contrast to laboratory assays, caterpillars survived exposure to prairie soil containing EPNs under natural conditions in field assays. To better understand the divergence between laboratory and field results for this native caterpillar, we used sentinel insects [Galleria mellonella L. (Lepidoptera: Pyralidae)] to identify particular locations where EPNs were present in the field. Platyprepia virginalis caterpillars were caged at these sites but again showed no evidence of susceptibility to EPNs. Platyprepia virginalis caterpillars reduce their exposure to EPNs by spending their time in and above the litter rather than contacting the soil when given the choice in nature. We conclude that P. virginalis is unlikely to serve as a reservoir for EPNs and that nematodes are unlikely to be important mortality factors for P. virginalis in this natural system.

The importance of host plant limitation for caterpillars of an arctiid moth (Platyprepia virginalis) varies spatially

“…In dry, upland sites populations may be limited by the availability of lupine hosts but lupine does not limit populations in more favorable wet sites. It is not clear at this point what does limit populations at favorable wet sites although we can also exclude tachinid parasitoids despite high rates of parasitism (Karban and de Valpine 2010), diseases including entomophagous nematodes (Karban et al 2011), and vertebrate predators (R. Karban, P. Grof‐Tisza, and M. Holyoak, unpublished data ). We have preliminary evidence that predation by ants and resource quality may be involved although a complete understanding of the relative importance of various factors over development in different habitats is still lacking.…”

Facilitation of tiger moths by outbreaking tussock moths that share the same host plants

“…In addition to food, litter may also provide a complex habitat that makes it harder for predators, such as ants, to find or handle young caterpillars (Freitas & Oliveira 1992). Young tiger moth caterpillars were also more vulnerable to entomopathogenic nematodes when there was no litter and spent most of their time above the soil surface and away from nematodes when this was possible (Karban et al. 2011).…”