Summary1. Cryptic coloration may evolve in response to selective pressure imposed by predators, yet effective intraspecific communication may require some level of detectability. This creates a tension between the benefits of sexually selected visual traits and the predatory costs imposed by greater conspicuousness, and little is known about how this tension may be ameliorated in highly cryptic species. 2. We explore these competing demands in the false garden mantid Pseudomantis albofimbriata, a colour-blind and seemingly cryptic insect. We use reflectance spectrometry and receptor-noise modelling to characterize the conspicuousness of mantid body regions in the visual systems of mates (mantids), as well as potential predators (birds) and prey (bees). We then use condition manipulation and conspecific choice tests to further explore the colour traits of interest. 3. Based on visual modelling, we find that male mantids are inconspicuous to conspecifics, prey and predators -that is, they are chromatically and achromatically cryptic. In contrast, female mantids are chromatically cryptic to all potential receivers, but their abdomens are achromatically conspicuous. Our food manipulation experiment shows that females in good condition (and therefore with more eggs) have brighter abdomens than females in poor condition. Choice assays show male mantids are consistently attracted to females bearing brighter abdomens. 4. Our results reveal brightness-mediated sexual signalling in a colour-blind and classically cryptic insect. By communicating in the only visual channel available to them, female mantids are conspicuously signalling their quality to mates, while potentially minimizing their conspicuousness to predators and prey. Furthermore, by signalling with only a single body region, female mantids are apparently using coincident disruptive coloration to further decrease detectability to potential eavesdroppers. 5. Our data reveal a novel example of the way in which the trade-off between sexual selection for conspicuousness and natural selection for crypsis may be mediated in a visual signalling system. Such signals may be common in apparently cryptic species, and this study once again demonstrates the importance of analysing visual signals beyond the capacity of human vision.

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BACKGROUND Queensland fruit fly (Q‐fly) is a destructive insect pest that infests a wide variety of agricultural plants in Australia. The sterile insect technique (SIT) is used to manage Q‐flies, but the effectiveness of SIT has not been tested in the presence of natural predators. The objective of this study was to investigate the effect of natural predators and SIT on the survival and reproduction of laboratory reared Q‐flies under semi‐natural conditions. We altered the presence of predators and irradiated Q‐fly males, and measured survival, number of eggs laid and egg‐hatching rate. RESULTS The presence of natural predators significantly affected the survival of Q‐flies and appeared to decrease the number of eggs laid. Interestingly, we found that both sterile and fertile males were more prone to predation than females, but we found no difference among males. The presence of sterile males significantly reduced Q‐fly fertility, but the interaction of natural predators and sterile males did not significantly reduce the number of fertile eggs. CONCLUSION Our findings highlight the important role of natural predators in controlling Q‐flies together with SIT and provide a solid foundation for similar large‐scale field trials using wild counterparts. © 2019 Society of Chemical Industry

Multiple mating by females is a common phenomenon in nature. Polyandrous females may benefit from genetically diverse progeny that may survive better in a changing environment. Males in polyandrous systems, however, may not achieve their maximum paternity. Therefore, males are predicted to carry traits that prevent or reduce female polyandry. Praying mantids are predatory insects in which females can mate multiple times, predicting the evolution of male counter-strategies. However, the rate of polyandry and male strategies against polyandry are rarely studied in these insects. In the current study, we used false garden mantids Pseudomantis albofimbriata to quantify the rate of multiple mating when several males are present within close visual range of an unmated female. We further determined how long mated females stay unattractive after mating. We found that in a scramble scenario, the subsequent males stay with a copulating pair and attempt mating once the first male has completed copulation. These second copulation attempts are often successful. If only one male is attracted as a result of the initial pheromone plume, then polyandry is unlikely because the female will remain chemically unattractive for 8 days on average (thus preventing subsequent male attractions), which is longer than the usual latency to lay the first egg sac. From previous studies, we know that single male attraction is the most common scenario in this system in both natural and semi-natural contexts. Therefore, polyandry depends on the number of males attracted to the initial pheromone plume of the female and is likely to be a relatively uncommon phenomenon in this system.