Host Plant Adaptations Among Geographic Populations of the Colorado Potato Beetle
- Entomologia Experimentalis et Applicata, 24(3), p.437-447, 1978 .
Intraspecific variation in host plant adaptation of an oligophagous insect is interesting because it signifies adaptive changes among populations of a given species and may play a key role in speciation. The Colorado potato beetle, Leptinotarsa decemlineata (Say), is an oligophagous feeder indigenous to the Americas, where it is widely distributed and infests some ten native and exotic solanaceous plants. The possible existence of host-adapted populations was investigated with four geographically isolated beetle populations collected from Solanum tuberosum and two native hosts, S. rostratum and S. elaeagnifolium. Host plant affinity was compared by rearing progeny from field adults on seven solanaceous hosts to assess growth performance and reproductive success of each population. Considerable differences were recorded among these populations on several hosts. The Arizona beetle is uniquely adapted to its natural host, S. elaeagnifolium, which is a typical unsuitable host for the Utah, New Mexico, and Texas beetles. This population also ranked most adaptable to the seven hosts tested. The Utah beetles were intermediate and the New Mexico and Texas beetles were the least adaptable. The evidence obtained so far strongly suggests that host-adapted populations are developing in North America. The finding implies that the formation of host races or biotypes among oligophagous insects must be preceded initially by geographic isolation of the preferred and non-preferred hosts so as to allow sufficient time for the insect population to develop adaptation to the less preferred hosts. The mechanism differs radically from that of some polyphagous species, in which host race or biotype formation occurs sympatrically without any evidence of geographic isolation.