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

Abstract

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.

Laboratory and field tests of predation on the cereal leaf beetle, Oulema melanopus (Coleoptera: Chrysomelidae)

“…My findings indicate high impacts of T. julis on CLB populations, expanding previous studies conducted at local scales (Dysart et al, 1973;Evans et al, 2015;Evans et al, 2006) to the landscape scale. CLB parasitism remained above the 32% minimum threshold for successful classical biological control (Hawkins & Cornell, 1994).…”

“…Because the impact of T. julis on CLB larval abundance happens the following year (i.e., parasitism does not decrease CLB abundance until the next generation), I hypothesize that this negative association is due to landscape-scale carryover effects of T. julis on CLB populations from previous years. The success of this parasitoid has been linked to its high specificity to CLB (Hervet et al, 2016), and high dispersal ability which resulted in no colonization lag between newly and previously planted wheat fields in disturbed agricultural landscapes (Evans et al, 2015). I conclude that CLB parasitism by T.…”

Zero‐sum landscape effects on acorn predation associated with shifts in granivore insect community in new holm oak (Quercus ilex) forests

“…From a metacommunity point of view (neutral-based models), habitat connectivity might help to promote mass effects on predator populations, thus increasing colonization success and damage on host plants across the landscape, while specific patch dynamics might help to promote or to arrest these landscape processes (Leibold et al, 2004). At a regional scale, more resilient species with poor dispersal abilities will gather in the older forests while species with higher dispersal abilities will be able to reach the new and more isolated ones (Evans, Bolshakova, & Carlile, 2015;Hendrickx et al, 2009;Hernández, Barreto, Costa, Creão-Duarte, & Favila, 2014). At a regional scale, more resilient species with poor dispersal abilities will gather in the older forests while species with higher dispersal abilities will be able to reach the new and more isolated ones (Evans, Bolshakova, & Carlile, 2015;Hendrickx et al, 2009;Hernández, Barreto, Costa, Creão-Duarte, & Favila, 2014).…”

“…Still, landscape attributes may also have a zero-sum effect on the host-predator interactions if there is merely a substitution of species among patches with a fixed total amount of resources. At a regional scale, more resilient species with poor dispersal abilities will gather in the older forests while species with higher dispersal abilities will be able to reach the new and more isolated ones (Evans, Bolshakova, & Carlile, 2015;Hendrickx et al, 2009;Hernández, Barreto, Costa, Creão-Duarte, & Favila, 2014). At the local scale, niche characteristics will take over and also play an important role in the compensatory dynamics that maintain the zero-sum.…”

Consumption of cereal leaf beetle, Oulema melanopus, by generalist predators in wheat fields detected by molecular analysis

“…Several researchers have investigated the effect of parasitism on CLB control (Evans et al, 2006(Evans et al, , 2015Kher et al, 2014), but few studies evaluated predator impacts on CLB populations (Shade et al, 1970;Kheirodin et al, 2019). Tetrastichus julis (Walker) (Hymenoptera: Eulophidae) is a classical biological control agent imported from Europe, which significantly impacts CLB populations, with up to 60% parasitism reported in Utah, USA (Evans et al, 2006).…”