|De Leon, Jesus|
Submitted to: Biological Control
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 3/15/2006
Publication Date: 5/12/2006
Citation: De Leon, J.H., Jones, W.A., Setamou, M., Morgan, D.J. 2006. Genetic and hybridization evidence confirms that a geographic population of Gonatocerus morrilli (Hymenoptera: Mymaridae) from California is a new species: egg parasitoids of the glassy-winged sharpshooter Homalodisca coagulata (Homoptera: Cicadellidae). Biological Control. 38:282-293. Interpretive Summary: In the present study, we investigated whether an egg parasitoid or natural enemy (Gonatocerus morrilli) of the glassy-winged sharpshooter (GWSS) exists in nature as a cryptic species complex. In a biological control project, it is crucial to genetically characterize or properly identify a natural enemy before it is released. Failure to release the proper natural enemy can lead to failure of the biological control program. DNA sequencing of certain standard genes provided evidence that geographic populations of G. morrilli were highly diverged, indicating that different or cryptic species existed. In addition, crossing studies of geographic populations of G. morrilli from Texas and California failed to produce offspring. The current results strongly confirm that these egg parasitoids are actually cryptic species and not geographic populations. The present studies are important to the biological control program in California against the GWSS. Since we previously demonstrated that the GWSS originated in Texas, it is important to collect these natural enemies (G. morrilli) from Texas.
Technical Abstract: We investigated the differentiation and reproductive isolation among geographic populations of the glassy-winged sharpshooter (Homalodisca coagulata) primary egg parasitoid, Gonatocerus morrilli, to confirm previous observations that it may exist in nature as 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 also clustered the TX/FL and CA populations or species into two well supported, distinctive clades. The nov. sp. G. morrilli 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 totally 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. Cytoplasmic incompatibility was ruled out as a cause for the lack of reproduction since all geographic populations were determined to be infected with the same strain of Wolbachia pipientis.