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. There also exist interactions among parasitoids, which finally shapes parasitoid load. Host range and parasitoid load are the most important issues in parasitoid community ecology. There is a great difference between the number of parasitoid species attacking different hosts. Hawkins collected a great deal of data about parasitoid load, but it s very troublesome in rearing various hosts.
Parasitoid load is influenced also by the competition among different parasitoids.
As an important molecular technique, molecular marker is very useful in basic and applied researches of microhymnoptera. Combined with traditional insect behavioral ecology, physiological ecology and chemical ecology, molecular marker technique can elucidate many important issues concerned about the mechanism of host selection of Trichogramma. This project is funded by the open foundation of the State Key Laboratory of Integrated Management of Insect and Rodent Pests in Agriculture, Institute of Zoology, Chinese Academy of Sciences.