CUTICULAR HYDROCARBON DISCRIMINATION OF DIABROTICA (COLEOPTERA, CHRYSOMELIDAE) SIBLING SPECIES

Cuticular hydrocarbons were extracted from adults of the sibling species Diabrotica longicornis (Say) and D. barberi Smith & Lawrence and characterized by gas chromatography (GC) and GC-mass spectrometry (GC-MS). Six classes of hydrocarbons were present: n-alkanes, terminally branched monomethylalkanes, internally branched monomethylalkanes, dimethylalkanes, n-alkenes, and monomethyl-branched alkenes. Diet and age did not significantly affect cuticular hydrocarbon patterns in most cases. However, when aged beetles were analyzed, the quantity of several cuticular hydrocarbons changed after the teneral stage. Some sexual dimorphism was seen in cuticular hydrocarbons of older beetles, but it did not significantly affect comparisons between species. Identical classification results were obtained when stepwise discriminant analysis using 13 cuticular hydrocarbons as variables was compared with visual identification of 60 reared beetles (34 D. longicornis and 26 D. barberi from allopatric populations). When additional reared and field- collected beetle profiles (from sympatric and allopatric populations) were entered into the discriminate analysis using the initial covariance matrix as a standard, there was 95% agreement with visual identification. These data suggest that, in most cases, the cuticular hydrocarbon analysis may be used to differentiate the sibling species regardless of their origin.