Thrips tabaci Lindeman is an extensively distributed pest insect that injures a wide range of crops. To investigate the intra-specific genetic diversity of this species, we analyzed an 810 bp region of the mitochondrial cytochrome oxidase gene subunit I (COI). Eight populations from six foreign countries and 18 Japanese populations were tested, and 17 different haplotypes were identified. Apparent differences were found between arrhenotokous and thelytokous strains in their COI sequences. A phylogenetic tree of the COI gene shows two distinct groups. We assume that these two groups correspond respectively to the arrhenotokous strain and the thelytokous strain. Japanese thelytokous types consisted of five haplotypes. Two haplotypes were identified from problematic populations in terms of the greater amount of damage they caused and the development of insecticide resistance. Both haplotypes were also found overseas, suggesting that some strains from overseas may have caused the above-mentioned problems in Japan.

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Bacillus thuringiensis strains produce insect-specific Bt toxins. Bt CryIA(a) toxin binds to a 175-kDa glycoprotein (BtR175) on the microvillus membranes of columnar cells in the Bombyx mori midgut and causes lysis of the cells. BtR175 was purified, and its cDNA was cloned. The cDNA encodes a newly identified 193.3-kDa preproprotein form of BtR175 that includes nine extracellular cadherin repeats, a 23.5-kDa membrane-proximal domain, a membrane-spanning region, and a 13.6-kDa cytoplasmic domain. Spodoptera frugiperda cells transfected with a recombinant baculovirus DNA carrying the cDNA produced a 175-kDa protein that reacted with anti-BtR antibodies and the Bt CryIA(a) toxin.

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The complete coding sequences of two acetylcholinesterase (AChE) genes, Ace1 (orthologous to Drosophila Ace) and Ace2 (paralogous to Ace), from the cotton aphid (Aphis gossypii) were identified and sequences from carbamate resistant and susceptible strains compared. No change in the amino acid sequences was found in Ace1, while two amino acid substitutions, Ser431Phe and Ala302Ser, were detected between resistant and susceptible strains in Ace2. The position of Ser431Phe corresponds to one of fourteen aromatic residues lining the active site gorge and is located in the acyl pocket. Ala302Ser is located at one of the three residues which form the oxyanion hole in the active site of AChE. The Ser431Phe and Ala302Ser substitutions may play a role in pirimicarb and organophosphate resistance, respectively.