Abstract:

The relationships between the susceptibility to neem seed extract and the allozyme genotypes were examined in the first instar nymphs of Tessaratoma papillosa (Drury) for two polymorphic enzyme loci of Pgi and Mdh using allozyme analysis. Acute exposures of the insect to 5.2 mg/mL (LC₅₀ value) neem seed extract resulted in 51.8% mortality in 24 h. Under the given experimental conditions, insect mortalities were significantly different among certain genotypes and alleles. At locus Pgi, the insects with the Pgi-bb genotype displayed the highest mortality (84%), whereas those with Pgi-aa and Pgi-cc showed the lowest mortalities (0 and 7%, respectively), which were significantly different from that of Pgi-bb. At locus Mdh, the insects with the genotype Mdh-cc and Mdh-aa exhibited the highest mortality (93%), but no mortality was observed in the insects with the genotype Mdh-cc. These results clearly indicated that the insects with genotype
Mdh-aa and Mdh-cc were significantly different from those with other three genotypes Mdh-ab, Mdh-bb and Mdh-bc in response to neem seed extract. In contrast, the mortalities of the insects with the Pgi-a and Mdh-c allele were the lowest, and were significantly different from those with other alleles. Our studies showed that individuals of T. papillosa with different genotypes had significantly different responses to neem seed extract. Such distinct relationships between the insect susceptibility to neem seed extract and its allozyme genotypes may allow us to use certain genotypes and alleles as genetic markers to assess the susceptibility of T. papillosa to neem seed extract.

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Key words: Tessaratoma papillosa, neem seed extract, allozymes, genotype, allele, selective lethal effect