Microorganisms associated with field-collected Chrysoperla rufilabris (Neuroptera: Chrysopidae) adults with emphasis on yeast symbionts

The indigenous gut microflora associated with the alimentary canal of 24 field-collected Chrysoperla rufilabris adults was examined qualitatively and quantitatively at five sample times and two locations in Mississippi. Yeasts were isolated from the diverticula of 17 insects, and there was no effect of location or sample time on the occurrence of yeasts. Metschnikowia pulcherrima was present in all of the diverticula that contained yeasts, and densities in this gut region ranged from 5.3 × 102 to 5.4 × 105 colony forming units (CFUs). Numerous yeast cells were observed in diverticula, and these cells accumulated within pronounced diverticular folds. Large numbers of Met. pulcherrima were also observed in the foregut, and to a lesser extent in the midgut and hindgut of field-collected adults. In an ancillary experiment, no yeasts were observed in Cry. rufilabris adults that had recently eclosed (ca. 24 h) in the laboratory. Thirteen of the insects were positive for filamentous fungi, but the majority of the gut regions contained <102 CFUs. Furthermore, there was very little commonality in the taxa isolated among the sample times and locations suggesting that filamentous fungi are transients in Cry. rufilabris alimentary canals. Nineteen insects were positive for bacteria. Populations varied among the gut regions, and more bacteria were recovered from the midguts of adults at one collection site. Twenty-five aerobic bacterial taxa were isolated, and Enterobacter aerogenes was the most commonly isolated taxon. However, this bacterium was only isolated from four insects on four occasions. Other bacterial taxa were even less frequently isolated, suggesting that bacteria are likely transients. Our findings indicate that Cry. rufilabris adults may form a symbiosis with the yeast, Met. pulcherrima, but not with filamentous fungi or bacteria. This information will facilitate studies to elucidate the mechanism and impact of this interaction, and may facilitate the rearing of this important predator for use in biological control programs against pest insects.