Characterization of the symbiont Rickettsia in the mirid bug Nesidiocoris tenuis (Reuter) (Heteroptera: Miridae).

Nesidiocoris tenuis (Reuter) (Heteroptera: Miridae) is an omnivorous insect used for biological control. Augmentative release and conservation of N. tenuis have been used for pest control in tomato crops. Intracellular bacterial symbionts of arthropods are common in nature and have diverse effects on their hosts; in some cases they can dramatically affect biological control. Fingerprinting methods showed that the symbiotic complex associated with N. tenuis includes Wolbachia and Rickettsia. Rickettsia of N. tenuis was further characterized by sequencing the 16S rRNA and gltA bacterial genes, measuring its amount in different developmental stages of the insect by real-time polymerase chain reaction, and localizing the bacteria in the insect's body by fluorescence in situ hybridization. The Rickettsia in N. tenuis exhibited 99 and 96% similarity of both sequenced genes to Rickettsia bellii and Rickettsia reported from Bemisia tabaci, respectively. The highest amount of Rickettsia was measured in the 5th instar and adult, and the symbionts could be detected in the host gut and ovaries. Although the role played by Rickettsia in the biology of N. tenuis is currently unknown, their high amount in the adults and localization in the gut suggest that they may have a nutritional role in this insect.

Biotype-dependent secondary symbiont communities in sympatric populations of Bemisia tabaci.

The sweet potato whitefly, Bemisia tabaci, harbors Portiera aleyrodidarum, an obligatory symbiotic bacterium, as well as several secondary symbionts including Rickettsia, Hamiltonella, Wolbachia, Arsenophonus, Cardinium and Fritschea, the function of which is unknown. Bemisia tabaci is a species complex composed of numerous biotypes, which may differ from each other both genetically and biologically. Only the B and Q biotypes have been reported from Israel. Secondary symbiont infection frequencies of Israeli laboratory and field populations of B. tabaci from various host plants were determined by PCR, in order to test for correlation between bacterial composition to biotype and host plant. Hamiltonella was detected only in populations of the B biotype, while Wolbachia and Arsenophonus were found only in the Q biotype (33% and 87% infection, respectively). Rickettsia was abundant in both biotypes. Cardinium and Fritschea were not found in any of the populations. No differences in secondary symbionts were found among host plants within the B biotype; but within the Q biotype, all whiteflies collected from sage harboured both Rickettsia and Arsenophonus, an infection frequency which was significantly higher than those found in association with all other host plants. The association found between whitefly biotypes and secondary symbionts suggests a possible contribution of these bacteria to host characteristics such as insecticide resistance, host range, virus transmission and speciation.

Assessment of genetic relationships in Cucurbita pepo (Cucurbitaceae) using DNA markers.

Cucurbita pepo (pumpkin, squash, gourd), an economically important species of the Cucurbitaceae, is extremely variable in fruit characteristics. The objective of the present study was to clarify genetic relationships across a broad spectrum of the C. pepo gene pool, with emphasis on domesticates, using AFLP, ISSR and SSR markers. Forty-five accessions were compared for presence or absence of 448 AFLP, 147 ISSR, and 20 SSR bands, their genetic distances (GDs) were estimated and UPGMA cluster analysis was conducted. The results obtained from these three marker systems were highly correlated (P << 0.001). Clustering was in accordance with the division of C. pepo into three subspecies, fraterna, texana and pepo, with the first two less distant to one another than to the last one. Within the clusters, sub-clustering occurred in accordance with fruit shape and size. The subsp. texana cluster consisted of six sub-clusters, one each for the representatives of its five cultivar-groups (Acorn, Crookneck, Scallop, Straightneck and Ovifera Gourd) and wild gourds. Within the subsp. pepo cluster, the representatives of two cultivar-groups (Zucchini and Orange Gourd) formed distinct sub-clusters and the representatives of two other groups (Cocozelle and Vegetable Marrow) tended to sub-cluster separately from one another but formed an assemblage with the representatives of the remaining group (Pumpkin). Within-group GDs were less than corresponding between-group GDs in nearly all comparisons. The smallest-fruited accession, 'Miniature Ball', appears to occupy a genetically central position within C. pepo.