Specificity of a Y‐linked gene in the flea beetle Phyllotreta nemorum for defences in Barbarea vulgaris

Abstract

A Y-linked gene (R-gene) in the flea beetle Phyllotreta nemorum L. (Coleoptera: Chrysomelidae: Alticinae) confer the ability of larvae to survive on types of the plant Barbarea vulgaris R.Br. (Brassicaceae) which are immune to attack by susceptible conspecifics. Two near-isogenic flea beetle lines were developed. The YE-line contained the Y-linked R-gene, and male larvae from this line survived on B. vulgaris. The ST-line did not contain the gene and did not survive on the plant. The YE-line had been developed through 8-9 generations of backcrosses (YE-males with ST-females) and the two lines were considered to be isogenic except for genes located on the Y-chromosome.A single copy of the Y-linked gene is sufficient to transfer a susceptible genotype (ST) into a resistant genotype (YE) which is able to utilize a plant that is immune to attack by specimens without R-genes. The Y-linked gene had no effects on survival on other plant species tested. The gene did not have any effect on developmental times and weights of adult beetles reared on other plants than B. vulgaris. Developmental times of larvae with the Y-linked gene were longer on B. vulgaris than on normal host plants, R. sativus and S. arvensis, but the adults obtained the same size on these plant species. No trade-offs of the Y-linked gene were discovered. The results suggest that the occurrence of the Y-linked gene is a derived trait which has enabled the flea beetle to expand its host plant range. The evolution of a host shift to B. vulgaris seems not to be favoured by the presence of this single gene.

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

“…(P. W. de Jong and J. K. Nielsen, unpublished data), and parasitoids kill their host by parasitizing them, it is likely that parasitism indeed reduces fitness of the flea beetles, which would satisfy condition one. Barbarea has also been found to be a less profitable host plant compared to the alternative host plants (in agreement with condition three ;Nielsen 1999;de Jong and Nielsen 2000); this was indeed the incentive for the present study (see above). In this research the remaining condition formulated by Berdegue et al (1996) was addressed, namely whether mortality caused by natural enemies is lower on Barbarea than on Sinapis, and whether this is related to the difference in phenology of the different host plants.…”

“…Amongst the results of earlier and ongoing studies (De Jong and Nielsen 1999, 2002Nielsen and De Jong 2005), one in particular has prompted us to initiate the work reported in this paper: the use of defended Barbarea as food by the resistant flea beetles clearly involved physiological costs. When the resistant flea beetle larvae used defended Barbarea as food, they developed slower than on other plants, including S. arvensis (Nielsen 1999). Moreover, homozygous resistant flea beetles appeared to suffer from high mortality on different plant species in laboratory experiments (de Jong and Nielsen 2000).…”

Occurrence of a feeding deterrent in Barbarea vulgaris (Brassicales: Brassicaceae), a crucifer unacceptable to the diamondback moth, Plutella xylostella (Lepidoptera: Plutellidae).

“…The feeding of P. nemorum is also prevented by the cardenolides and cucurbitacins in Erysimum and Iberis (Nielsen, 1978). Interestingly, a race of P. nemorum which can utilize B. vulgaris, however, does not accept Erysimum and Iberis (Nielsen, 1999), also suggesting the presence of unknown feeding deterrents or toxins in B. vulgaris. It will be of interest to see whether the feeding deterrents against P. xylostella and P. nemorum are identical.…”

Identification of Defense Compounds inBarbarea vulgarisagainst the HerbivorePhyllotreta nemorumby an Ecometabolomic Approach

“…A stock of Phyllotreta nemorum from the ST line was maintained at 24°C and an 18-h-light/6-h-dark photoperiod as previously described (Nielsen, 1997a). The ST line is susceptible: it does not contain R genes that confer resistance to G-type and is unable to survive on the G-type of B. vulgaris arcuata (Nielsen, 1999).…”