|De Leon, Jesus|
Submitted to: CDFA Pierce's Disease Control Program Research Symposium
Publication Type: Proceedings
Publication Acceptance Date: 11/7/2005
Publication Date: 12/1/2005
Citation: De Leon, J.H., Jones, W.A., Setamou, M., Morgan, D.J. 2005. Discovery of a cryptic species complex in Gonatocerus morrilli (Hymenoptera: Mymaridae), a primary egg parasitoid of the glassy-winged sharpshooter. Proceedings of CDFA Pierce's Disease Control Program Research Symposium, December 5-7, 2005, San Diego, California. p. 302-305. Interpretive Summary: In order for a biological control program to be successful, it is crucial to genetically characterize the natural enemies before releasing them against a pest of interest. Even though natural enemies may look alike physically or morphologically, they may be gentically different; thus if the correct species is not identified, it could lead to failure of the biological control program. A natural enemy of the glassy-winged sharpshooter (GWSS), Gonatocerus morrilli, was genetically characterized in the present study. Standard genetic analyses were performed, that is sequencing of several genes (mitochondrial cytochrome subunit 1 and II (COI and COII) and the internal transcribed spacer region 2 (ITS2)). In addition, hybridization or crossing studies were performed to confirm the compatibility between geographic populations of G. morrilli. The results of the current study confirm that G. morrilli exist in nature as a cryptic species complex, meaning that they are physically alike but genetically different. These results are very important to the biological control program in California against the GWSS. In addition, since we previously demonstated that the GWSS that invaded California originated from Texas, it is important to collect the correct G. morrilli from Texas, since these natural enemies co-evolved with the GWSS in Texas and not with the closely related smoke-tree sharpshooter in California.
Technical Abstract: We investigated the differentiation and reproductive isolation among different geographic populations of Gonatocerus morrilli, an egg parasitoid of the glassy-winged sharpshooter (GWSS) (Homalodisca coagulata Say) (Homoptera: Cicadellidae), to confirm previous observations that there may exist a cryptic species complex. Two mitochondrial genes [cytochrome oxidase subunits I (COI) and II (COII)] and the internal transcribed spacer region 2 (ITS2) of several individuals per population were sequenced. Gonatocerus morrilli populations from Texas (TX), Florida (FL), California (CA), and an outgroup (G. ashmeadi) were analyzed. For comparison, a population from Argentina identified as near G. morrilli (=G. annulicornis) was also included. For all three sequence fragments, percentage sequence divergence (%D) demonstrated that both the TX and FL populations (TX/FL) were closely related and, therefore, determined to be the same species; in contrast, the %D between TX/FL and CA fell within the range of the outgroup, making the CA population a novel species (nov. sp. G. morrilli). Neighbor-joining distance trees clustered the TX/FL and CA populations or species into two well supported distinctive clades. The G. morrilli (nov. sp.) was more closely related to G. annulicornis than to the TX/FL species. Mating studies demonstrated that the populations or species from CA and TX were reproductively incompatible, producing no female offspring in both direct and reciprocal crosses, whereas the heterogamic crosses between TX and FL produced fertile offspring and relative compatibility indices similar to the homogamic crosses. These results are important to the PD/GWSS biological control program in California.