Geographic differentiation between populations of Rhinocyllus conicus Frölich (Coleoptera: Curculionidae): concordance of allozyme and morphometric analysis

Abstract

The weevil Rhinocyllu conicus develops only in the flowerheads of thistles {Asteracea; Carduineae) and therefore it is used as a biocontrol agent against thistle weed species. Populations out of 14 regions within its natural distribution area (from the Atlantic coast in the west to Israel in the east) were analysed by means of allozymes and morphometries. In both analyses the 14 populations were grouped into two concordant units. Based on nine scored loci (six of them polymorphic), mean Nei's genetic distance between the two groups was 0.073. In a reclassification test following DFA of morphometric data, 93.2% of all individuals were grouped back into the correct group. The two groups were considered to belong to a temperate and a Mediterranean subspecies respectively, the latter probably identical to the formerly described Rhinocyllus oblongus.

Rhinocyllus conicus : initial evaluation and subsequent ecological impacts in North America.

“…These traits -smaller size, plus earlier and shorter oviposition periodcould be adaptations related to use of Silybum species. Klein and Seitz (1994) suggested that the two groups represented subspecies, and they proposed that the Mediterranean subspecies was equivalent to the taxon previously described as Rhinoc)'llus oblongus Cap. In summary, the evidence now suggests that differences in host use or preference between the two groups (subspecies) of weevils may have a genetic component, whereas differences in host use within each subspecies of R. conicus are probably related to temporal availability of flowerheads (Klein, 1986(Klein, , 1991.…”

“…These perspectives lead to the expectation of insignificant levels of non-target feeding on native North American Cirsium species by R. conicus from C. nutans. The existence of host-plant biotypes in R. conicus has been challenged recently (Klein, 1991;Klein and Seitz, 1994).…”

“…Clearly, these observations suggest that genetic variation occurs among populations of R. conicus. Interpretation of how that variation is partitioned is now being revised (Klein, 1991;Klein and Seitz, 1994).…”

“…They showed that the populations divided into two well-differentiated, concordant groups on both sets of criteria (Klein, 1991;Klein and Seitz, 1994). The groups segregated into a north temperate group and a more southern, Mediterranean climate group, dividing at about the same latitude as the northern distribution border of the cultivated olive tree (Klein and Seitz, 1994). The R. conicus adults of the Mediterranean group had a narrower body, a 4 week earlier activity period, and a shorter oviposition period than did those of the temperate group.…”

Effectiveness of Gall Inducers in Weed Biological Control

“…Weevils from C. nutans are smothered by callus if they attack S. marianum, which is exploited by R. oblongatus Cap. (Klein and Seitz 1994). In Saskatchewan, the number of larvae per capitulum and the attack of secondary capitula are lower when spring is dry (Zwölfer and Harris 1984), so moisture may be a limiting factor.…”