No parasitoid can successfully parasitize all hosts in its surroundings. Generally speaking, host range is affected by two factors, i.e. host suitability and parasitoid s behaviors. Studying host range is more difficult than parasitoid load, because the data for host range study are much harder to collect. According to the current catalogs, the biggest problem is the taxonomy of parasitoids. The two key factors deciding host range are host taxonomy and shared ecology of hosts.
Environmental constancy can also affect host range.
Experiments showed that constant environment can promote host specialization. Hosts feeding on early successional plants have fewer specialists than those feeding on late successional plants, because these hosts are less predicatable to parasitoids. Molecular markers are obviously advantageous for host range study. The biggest problem in traditional investigations is the rearing of hosts, and incapability of direct collection of field data. Molecular marker can solve these problems, and may be used in studies on parasitoid population, spatial distribution, parasitism and food webs in nearly real-time ways.