We investigated the fate of ingested Enterobacter (Pantoea) agglomerans and Klebsiella pneumoniae within adult Mediterranean fruit fly, Ceratitis capitata (Wiedemann) (Diptera: Tephritidae), in a mass rearing facility. This examination revealed the establishment of both bacterial strains as biofilms within the adult intestines, on the apical end of developing and developed eggs, and throughout all subsequent life stages. The bacteria were detected in adults through two generations. Irradiation treatment for the sterile insect technique did not disrupt the vertical transmission of E. (P.) agglomerans or K. pneumoniae. This is the first demonstration of maternal spread of Enterobacter/ Pantoea spp. and Klebsiella spp. through populations of C. capitata. A mixed pattern of vertical and horizontal transmission of symbionts associated with tephritids may be one explanation for the difficulty in defining the symbiotic associations of tephritids.

Midguts from adult sterile male Ceratitis capitata Wiedemann and Anastrepha ludens Loew, the Mediterranean fruit fly and Mexican fruit fly, respectively, were examined microscopically to determine if radiation used in sterile insect technique (SIT) affected this non target tissue and/or the microorganisms associated with the midgut. Scanning and transmission electron microscopy were used to compare midgut tissues and microorganisms from irradiated and nonirradiated mass-reared adult flies. Observations for both fruit fly species were similar. Our comparisons revealed that newly emerged and two-day-old irradiated flies exhibited signs of damage to midgut tissue, cellular organelles, and gut microbiota not observed in nonirradiated flies of the same ages. Peritrophic membrane formation and bacterial growth appeared diminished in the midguts of irradiated flies compared to nonirradiated flies. Cellular damage of midgut tissue from irradiated flies included distorted, small nuclei that lacked nuclear material, and mitochondria that were dilated and/or vacuolated. No visual evidence of cellular damage was observed in nonirradiated flies. The impact of radiation used in SIT on fly competitiveness, referred to herein as the capability of adult flies to perform a function, is discussed, including the potential use of probiotic diets to improve damaged midgut tissue and restore midgut microbiota.

The perpetuation of symbiotic associations between bark beetles (Coleoptera: Curculionidae: Scolytinae) and ophiostomatoid fungi requires the consistent transport of fungi by successive beetle generations to new host trees. We used scanning electron microscopy and culture methods to investigate fungal transport by the mountain pine beetle (MPB), Dendroctonus ponderosae Hopkins. MPB transports its two main fungal associates, Grosmannia clavigera (Robinson-Jeffrey and Davidson) Zipfel, de Beer and Wingfield and Ophiostoma montium (Rumbold) von Arx, in sac-like mycangia on the maxillary cardines as well as on the exoskeleton. Although spores of both species of fungi were observed on MPB exoskeletons, often in pits, O. montium spores were generally more abundant than G. clavigera spores. However, a general scarcity of spores of either species on MPB exoskeletons compared with numbers on scolytines that lack sac-like mycangia indicates that fungal transport exteriorly on MPBs is incidental rather than adaptive. Conidia were the dominant spore type transported regardless of location or species; however, our results suggest that once acquired in mycangia, conidia may reproduce in a yeast-like form and even produce hypha-like strands and compact conidiophore-like structures. Fungi that propagate in mycangia may provide beetles with a continual source of inocula during the extended egg-laying period.