Molecular taxonomic analysis of the plant associations of adult pollen beetles (Nitidulidae: Meligethinae), and the population structure ofBrassicogethes aeneus

Abstract

Pollen beetles (Nitidulidae: Meligethinae) are among the most abundant flower-visiting insects in Europe. While some species damage millions of hectares of crops annually, the biology of many species is little known. We assessed the utility of a 797 base pair fragment of the cytochrome oxidase 1 gene to resolve molecular operational taxonomic units (MOTUs) in 750 adult pollen beetles sampled from flowers of 63 plant species sampled across the UK and continental Europe. We used the same locus to analyse region-scale patterns in population structure and demography in an economically important pest, Brassicogethes aeneus. We identified 44 Meligethinae at ∼2% divergence, 35 of which contained published sequences. A few specimens could not be identified because the MOTUs containing them included published sequences for multiple Linnaean species, suggesting either retention of ancestral haplotype polymorphism or identification errors in published sequences. Over 90% of UK specimens were identifiable as B. aeneus. Plant associations of adult B. aeneus were found to be far wider taxonomically than for their larvae. UK B. aeneus populations showed contrasting affiliations between the north (most similar to Scandinavia and the Baltic) and south (most similar to western continental Europe), with strong signatures of population growth in the south.

The potential of crop management practices to reduce pollen beetle damage in oilseed rape

“…Pollen beetles often feed on early spring-flowering plants before they move onto oilseed rape (Free and Williams 1978;Ouvrard et al 2016), and have been observed on the crop at pre-green bud growth stages (Veromann et al 2012); during most seasons, it seems that the beetles arrive sufficiently early to colonise even the most advanced crops before the susceptible green bud stages are over (Cook et al 2006;Mauchline et al 2017a). Relative differences in growth stage, for example between a crop and trap crop or variation within a field, however, are very important in determining infestation levels, because of the beetle's preference for the flowering growth stages (Cook et al 2007;Mauchline et al 2017a), which may provide a reliable cue for the availability of buds of the preferred size for oviposition (2-3 mm; Ekbom and Borg 1996), together with food resources (Frearson et al 2005).…”

“…Meligethes aeneus) (Coleoptera: Nitidulidae), a key pest of oilseed rape Brassica napus L. (OSR), a crop widely grown for cooking oil and biofuel use (EU production 19.8 M tonnes in 2016;Eurostat 2017); in this case, beetle resistance to pyrethroid insecticides, which are often applied prophylactically, has become a major problem (Zimmer et al 2014;Thieme et al 2010). Adult beetles emerge in early spring from overwintering habitats in woodlands and grassy areas (Rusch et al 2012;Blazejewska 1958;Müller 1941), and feed on the flowers of many different plants before seeking OSR crops and other brassicas at the green bud growth stage, for further feeding and oviposition (Free and Williams 1978;Ouvrard et al 2016). Feeding damage causes OSR flower bud abscission, leading to often extensive yield losses (Zlof 2008) that can approach 80% (Hansen 2004).…”

“…After eggs are laid in the buds, the developing larvae feed for c. 2 weeks before dropping to the soil to pupate. New generation adults emerge in summer and again feed on pollen from plants of several families before overwintering (Williams 2010;Alford et al 2003;Ouvrard et al 2016). The beetles are attacked at the larval stage by a range of parasitoid species, the most abundant and widespread of which in Europe are Tersilochus heterocerus Thomson, Phradis interstitialis Thomson and Phradis morionellus Holmgren (Ulber et al 2010b); surface-active and plant-climbing natural enemies include ground beetles and spiders Frank et al 2010).…”

Semiochemical-based alternatives to synthetic toxicant insecticides for pollen beetle management

“…This is the first behavioural process in the pollen beetle life cycle that is known to be strongly influenced by semiochemical cues (reviewed by Williams and Cook 2010). Overwintered adult pollen beetles are generalist feeders on pollen from many different plant families to obtain nutrients for energy (Roulston and Cane 2000) and ovary maturation Ouvrard et al 2016). Pollen beetles locate their food host-plants, which include Brassicas, using a variety of plant semiochemical and visual cues.…”

“…Pollen beetles have been found feeding on a wide variety of wild plants Mauchline 2003;Ouvrard et al 2016) and are known to respond positively to whole plant odours from several non-Brassicaceous species including dandelion (Taraxacum officinale L.) (Cook 2000), field bean (Vicia faba L.) (Cook 2000), rye (Secale cereale L.) (Ruther and Thiemann 1997), tomato (Solanum lycopersicum L.) (Ruther and Thiemann 1997) and yarrow (Achillea millefolium L.) (Ruther and Thiemann 1997). Some of the semiochemicals responsible for this attraction have been identified.…”