Gene silencing through RNA interference (RNAi) has revolutionized the study of gene 98 function, particularly in non-model insects. However, in Lepidoptera (moths and butterflies) 99 RNAi has many times proven to be difficult to achieve. Most of the negative results have been 100 anecdotal and the positive experiments have not been collected in such a way that they are 101 possible to analyze. In this review, we have collected detailed data from more than 150 102 experiments including all to date published and many unpublished experiments. Despite a 103 large variation in the data, trends that are found are that RNAi is particularly successful in the 104 family Saturniidae and in genes involved in immunity. On the contrary, gene expression in 105 epidermal tissues seems to be most difficult to silence. In addition, gene silencing by feeding 106 dsRNA requires high concentrations for success. Possible causes for the variability of success 107 in RNAi experiments in Lepidoptera are discussed. The review also points to a need to further 108 investigate the mechanism of RNAi in lepidopteran insects and its possible connection to the 109 innate immune response. Our general understanding of RNAi in Lepidoptera will be further 110 aided in the future as our public database at http://insectacentral.org/RNAi will continue to 111 gather information on RNAi experiments.
Gram-positive spore-forming entomopathogenic bacteria can utilize a large variety of protein toxins to help them invade, infect, and finally kill their hosts, through their action on the insect midgut. These toxins belong to a number of homology groups containing a diversity of protein structures and modes of action. In many cases, the toxins consist of unique folds or novel combinations of domains having known protein folds. Some of the toxins display a similar structure and mode of action to certain toxins of mammalian pathogens, suggesting a common evolutionary origin. Most of these toxins are produced in large amounts during sporulation and have the remarkable feature that they are localized in parasporal crystals. Localization of multiple toxin-encoding genes on plasmids together with mobilizable elements enables bacteria to shuffle their armory of toxins. Recombination between toxin genes and sequence divergence has resulted in a wide range of host specificities.
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