Determination of wild host plants as possible sources of pest insects is important for integrated crop management in cultivated areas. We first clarified biotypes of the whitefly, Bemisia tabaci, infesting non-crop plants (36 species in 14 families) throughout the Ryukyu Islands, which are subtropical areas in Japan. The B biotype, the most common biotype on crop plants in this area, was found on 32 non-crop plant species (in 13 families), and frequently infested asteraceous and euphorbiaceous weeds; therefore, control of these weeds is important for integrated management of the B biotype in the Ryukyu Islands. The Nauru biotype had a narrower host range, and was found on 13 plant species (in 6 families). The Q biotype was found only once on a Solanum weed. One biotype belonging to the genetic group ‘China’ was identified from two plant species growing on the seashore.
To discriminate between arrhenotokous and thelytokous forms of the onion thrips (Thrips tabaci), we developed a simple molecular diagnostic method that uses PCR-RFLP of the mitochondrial cytochrome c oxidase subunit I (COI) gene. Digestion of 490-bp COI amplicons with EcoO109I provided reproductive form-specific RFLP patterns. Using this method, we surveyed the frequencies of the two reproductive forms in 9 Welsh onion fields in Tottori Prefecture. Arrhenotoky dominated in the western area, although 100% of individuals were thelytokous in the eastern area. The COI haplotype of the arrhenotokous individuals was haplotype 1 or 2, which has not previously been found in Japan.