Most sharpshooter species found in California have some capacity to transmit the plant bacterial pathogen Xylella fastidiosa, the causal agent of Pierce's Disease (PD) in grapes; however, their economic impact differs considerably. The glassy-winged sharpshooter (GWSS) Homalodisca coagulata is by far the most serious species, while the closely related smoke tree sharpshooter (STSS) H. lacerta is less important. Both species occur sympatrically on several hosts where they lay their eggs beneath the epidermis of the undersides of leaves. Although the STSS eggs are generally considered to be smaller, there is broad overlap in size between the two species' eggs, making an absolute diagnosis impossible until the emergence of the first nymphal instar. It would be an advantage to be able to distinguish between species at the egg stage, as this would offer the possibility of an early detection system capable of signaling future pest problems.
Esterases have proved to be an important enzyme system for studies on insect taxonomy and for distinguishing between insect biotypes. One of the more attractive features of insect esterases is that there are often several polymorphic loci present, thereby enhancing the prospect of distinguishing between closely related species or even strains/biotypes of the same species. Esterase profiling would provide an effective means of monitoring sharpshooter egg populations to establish the frequencies of the two species in different crop systems. This could have important implications for targeting chemical control measures against emerging immatures.
In this report we describe our isoenzyme studies of GWSS and STSS insects collected from Southern California citrus orchards and vineyards. We discuss the value of such a technique for (1) distinguishing the two species from their egg isoenzymes and (2) detecting and monitoring the spread of the GWSS in new geographical locations.
The ESA 2001 Annual Meeting - 2001: An Entomological Odyssey of ESA