There is ample evidence that host shifts in plant-feeding insects have been instrumental in generating the enormous diversity of insects. Changes in host use can cause host-associated differentiation (HAD) among populations that may lead to reproductive isolation and eventual speciation. The importance of geography in facilitating this process remains controversial. We examined the geographic context of HAD in the wide-ranging generalist yucca moth Prodoxus decipiens. Previous work demonstrated HAD among sympatric moth populations feeding on two different Yucca species occurring on the barrier islands of North Carolina, USA. We assessed the genetic structure of P. decipiens across its entire geographic and host range to determine whether HAD is widespread in this generalist herbivore. Population genetic analyses of microsatellite and mtDNA sequence data across the entire range showed genetic structuring with respect to host use and geography. In particular, genetic differentiation was relatively strong between mainland populations and those on the barrier islands of North Carolina. Finer scale analyses, however, among sympatric populations using different host plant species only showed significant clustering based on host use for populations on the barrier islands. Mainland populations did not form population clusters based on host plant use. Reduced genetic diversity in the barrier island populations, especially on the derived host, suggests that founder effects may have been instrumental in facilitating HAD. In general, results suggest that the interplay of local adaptation, geography and demography can determine the tempo of HAD. We argue that future studies should include comprehensive surveys across a wide range of environmental and geographic conditions to elucidate the contribution of various processes to HAD.

1. Specialisation in host plant use is strongly correlated with speciation in many plant-feeding insects. Specialised taxa, however, could be restricted in host range due to limits in ecological availability of host plant species rather than trade-offs in using alternate host species.2. Moths in the genus Prodoxus are extreme specialists on Yucca and speciation is closely tied to host plant shifts. However, many Yucca ranges are allopatric. This study examined whether the bogus yucca moth Prodoxus decipiens is limited in host range because of biogeographic factors or due to differences in the characteristics of host plant species.3. In a common garden, local P. decipiens moths that use Yucca filamentosa were exposed to individuals of five Yucca species, two that are known hosts of P. decipiens in other parts of its range and three that are used by its sister species, Prodoxus quinquepunctellus.4. Local moths were attracted to flowers of all Yucca species and females attempted oviposition in the flowering stalks of all species. However, larvae successfully completed development to diapause in only one of the five host plant species. Larval development on non-natal Yucca species was significantly reduced compared with the local host.5. The results suggest that differences in host plant characteristics among Yucca species would result in strong natural selection during a host shift. Thus, specialisation in host plant use is probably due to trade-offs involved with using novel host plant species as well as ecological availability.

It is now common for computer-aided engineering tools to show a performance parameter — like von Mises stress — over the surface of a solid part. In this paper, a heatmap is generated for part cost where high values (shown in red) indicate regions with a high impact on manufacturing cost. This is accomplished by slicing the provided part many times in multiple orientations and evaluating the total costs of each side of the part at each slice. The costs from all the directions considered are combined to generate a heatmap to show how different regions affect cost, enabling the designer to make informed improvements to the part geometry. In this paper, our method for generating these heatmaps is presented with three primary manufacturing cost models: bar stock, forging, and metal 3D printing. In all cases, a machining operation is then applied to get to the final part shape. Results are shown to validate the approach and demonstrate its usefulness.