Variation in defences of the plant Barbarea vulgaris and in counteradaptations by the flea beetle Phyllotreta nemorum

Abstract

Several sorts of variation in the interaction between the insect, Phyllotreta nemorum L. (Coleoptera: Chrysomelidae: Alticinae), and the plant, Barbarea vulgaris R.Br. (Brassicaceae), have been discovered: 1) genetic differences in the levels of defences in the plant, 2) genetic differences in the ability of insects to cope with the plant defences, 3) seasonal variation in levels of defences in the plant, and 4) differences between leaf types in levels of defences.Two plant accessions were suitable for larval development throughout the season while the remaining nine accessions were more or less unsuitable for larvae from the 'susceptible' T-population at least at certain times of the year. All accessions were suitable for the 'resistant' E-population throughout the year. There was a seasonal variation in levels of defences in some accessions which were unsuitable for the T-population during the summer period when beetles were present, but not during autumn and spring when the beetles were hibernating. Upper (younger) cauline leaves of these accessions had higher levels of defences than lower (older) cauline leaves. The resistant E-population used B. vulgaris as a natural host plant while the susceptible T-population did not. The use of B. vulgaris as a natural host plant by the E-population of P. nemorum seems to be an extension of the host plant range of the species. Variation in plant defences may have facilitated the switch in host plant use by the resistant flea beetle population.

The chemical world of crucivores: lures, treats and traps

“…Nielsen (1997a) found that different types of B. vulgaris arcuata differ dramatically in their resistance to the flea beetle, Phyllotreta nemorum. These plant populations have been described as a 'G-type', with glabrous leaves and a 'P-type', which has pubescent leaves.…”

“…The P-type is susceptible to the flea beetle, whereas the G-type is generally resistant. In addition to these genetic differences in levels of defense, Nielsen (1997a) found that seasonal variation and differences between leaf type occur. Subsequent work revealed the existence of populations of the flea beetle that could deal with this plant resistance to feed successfully on the G-type of the subspecies (Nielsen, 1997b).…”

Chemical diversity in Brassica oleracea affects biodiversity of insect herbivores

“…Therefore, variation in plant traits may significantly influence ecosystem biodiversity (Dungey et al 2000, Hochwender and Fritz 2004, Wimp et al 2005, Poelman et al 2008c (Dungey et al 2000, Johnson and Agrawal 2005, Bangert et al 2006. Variation in phytochemistry of plant genotypes may include quantitative or qualitative differences in only a few chemical compounds, and phytochemical composition may be heritable (van Dam and Vrieling 1994, Nielsen 1997, van Leur et al 2006). Intraspecific differences in foliar chemical profiles, i.e., the qualitative composition of the mix of phytochemicals, may have extensive consequences for ecosystem biodiversity and especially affect species that are in close reciprocal interaction with plants, such as herbivorous insects (Johnson and Agrawal 2005).…”

Detection of refuge from enemies through phenological mismatching in multitrophic interactions requires season-wide estimation of host abundance

“…Whereas parasitism on Barbarea is higher than on Sinapis at any particular moment (orange bars higher than brown ones), the parasitism of the cohort of flea beetles on Barbarea across the whole season is lower than on Sinapis Evol Ecol (2011) 25:485-498 487 de de Jong and Nielsen 2002;Renwick 2002). Resistant flea beetles are relatively rare, which has led to the hypothesis that the use of Barbarea represents a hostrange expansion of P. nemorum (Nielsen 1997). The genotype of B. vulgaris ssp.…”

“…nemorum has one generation per year in Denmark, and adults overwinter in diapause in the soil. Eggs are laid in the soil close to the host plants, and newborn larvae climb into a nearby plant, after which they start mining its leaves (Nielsen 1997). The larvae of P. nemorum are known to be attacked by at least five hymenopteran parasitoids (Ulber and Williams 2003), including Diospilus morosus Reinhardt (Braconidae) and Aneuclis brevicauda Thomson (Ichneumonidae).…”