Host utilization is mediated by movement of pre‐feeding Phthorimaea operculella larvae in the Nicotiana tabacum agroecosystem

Abstract

AbstractThe distribution of insect herbivores within their hosts can be influenced by insect preference, plant characteristics, and biotic interactions such as refuge from predation. We observed significantly more Phthorimaea operculella (Zeller) (Lepidoptera: Gelechiidae) larvae in the lower portion of commercial tobacco plants, Nicotiana tabacum L. (Solanaceae), an occasional host, and sought to explain this distribution pattern. Phthorimaea operculella are oligophagous leaf miners of solanaceous plants, including cultivated crops. Females lay their eggs in the soil beneath N. tabacum plants rather than on the foliage, forcing newly hatched larvae to search for host tissue. We hypothesized that P. operculella larvae were establishing in the lower portion of N. tabacum plants because either they gained a performance advantage, or it was the first suitable leaf material contacted. To measure within‐plant larval performance, neonates were released in cages on leaves in the upper, middle, and lower stalk positions of the plant before and after the plant flowered. Phthorimaea operculella performed significantly better on younger plants and in the top leaves. To test larval ability to move within and between plants, we removed leaves at four heights to increase the distance newly hatched larvae must travel. Larval establishment was highest on plants with no leaves removed, but larvae were able to move an average distance of over 70 cm from release point to host leaves in plants directly above the release point and adjacent plants. Phthorimaea operculella larvae appear to utilize suboptimal N. tabacum host tissue to maximize their chances of survival.