Phenology and impact of natural enemies associated with the hop looper (Hypena humuli) in Washington State, USA

Abstract

The hop looper, Hypena humuli Harris (Lepidoptera: Noctuidae), is becoming an increasingly important pest of hops (Humulus lupulus L.) (Rosales: Cannabaceae) in western USA. Currently, control of this pest usually involves broad-spectrum pesticides that kill natural enemies and disrupt biological control of other hop pests. In order to develop better management strategies for H. humuli, field and laboratory studies were conducted over a four-year period to identify the pest's natural enemies and to investigate their phenologies and to assess their impact. Nine parasitoid species and assorted species of invertebrate predator were found to attack different life-stages of H. humuli. Levels of parasitism were consistently low throughout the study period and none of the parasitoids found was a specialist natural enemy of the pests. Exclusion cage studies showed, however, that the complex of natural enemies as a whole can significantly reduce larval densities of the pest, and laboratory studies confirmed successful predation of H. humuli larvae by several generalist predators including the European earwig (Forficula auricularia L.), the damsel bug Nabis alternatus Parshley and two species of the geocorid bug genus Geocoris.

Keywords:

• hops
• Humulus lupulus
• Hypena humuli
• natural enemies
• parasitism
• phenology
• predation

Acknowledgements

We thank the Washington Hop Commission and the Washington State Commission for Pesticide Registration for financial support for this project, Noel Hinojosa, Laura Matson, Alison Sipe and Jesse Fulbright for assistance with field work, and two anonymous referees for their comments. We are also indebted to the following taxonomists from the Systematic Entomology Laboratory USDA-ARS) for identification of predator and parasitoid species: Norman E. Woodley (Tachinidae), Robert W. Carlson (Ichneumonidae), E. Eric Grissell (Pteromlaidae), and Thomas J. Henry (Geocoidae and Nabidae).