Parasitoid dispersal and colonization lag in disturbed habitats: biological control of cereal leaf beetle metapopulations

Natural enemies of insect pests of annual crops have been hypothesized either to lag, or alternatively not to lag, behind their prey in dispersing to and colonizing new habitat. We examined parasitoid dispersal and parasitism of the cereal leaf beetle (Oulema melanopus [L.]; Coleoptera: Chrysomelidae) by the host‐specific wasp Tetrastichus julis [Walker] (Hymenoptera: Eulophidae) in wheat fields of northern Utah to assess whether a colonization lag occurred. Equally high rates of parasitism of beetle larvae (including second instars early in the year) occurred in 2010 and 2011 in fields that were newly planted to wheat vs. in fields where wheat had been grown also the previous year. A caging experiment demonstrated that parasitism in these newly planted wheat fields did not arise from parasitoid adults that had matured within the fields; instead, upon emerging in other fields, parasitoid females dispersed a minimum of 100–250 m to parasitize beetle larvae early in the spring in the newly planted fields. A transect study in 2012 revealed that T. julis females dispersed rapidly at least 600 m into a newly planted wheat field to parasitize most of the early maturing beetle larvae, which occurred at very low density. Thus, the parasitoid has very strong ability to match its host in dispersal over long distances across a highly disturbed agricultural landscape, and colonization lag appears of little importance in affecting biological control associated with this host–parasitoid interaction.