Rate of soil egestion by larvae of Hylamorpha elegans (Burm.) and Phytoloema hermanni Germ. (Coleoptera: Scarabaeidae)

ABSTRACT

Larvae of Hylamorpha elegans (Burm.) and Phytoloema herrmanni Germ. feed on roots, although many Scarabaeidae species are able to feed and survive on soil without living roots. In this study we evaluated the potential of H. elegans and P. herrmanni to ingest soil by estimating the rate of soil egestion. In the laboratory, the rate of soil egestion was determined from gut content and gut transit time of 3rd-instar larvae feeding on soil without roots. The soil egestion rate was 14-21 mg g-1 d-1 for H. elegans and 11-16 mg g-1 d-1 for P. herrmanni. The gut transit time (time of soil passage from mouth to anus) was 2-3 d for both species and the gut content was 41 ± 2 mg g-1 for H. elegans and 32 ± 2 mg g-1 for P. herrmanni. The quantitative importance of feeding activity on soil depends upon the population density of larvae in the field, which ranges from 1 to 25 larvae m-2, but in severe outbreaks can reach 300 larvae m-2. High population densities could result in soil egestion rates reaching 20 kg d-1 ha-1 for P. herrmanni and 30 kg d-1 ha-1 for H. elegans.