Coccinellida defensive mechanism11/19/2022 ![]() We hypothesized that all investigated haemolymph parameters and body mass are negatively affected by repeated reflex bleeding in addition, we expected this effect to be strengthened by limited food availability because valuable components of haemolymph are lost during reflex bleeding (e.g., alkaloids, haemocytes and proteins with various functions) 16, 17, 18. We also measured the effects of frequent reflex bleeding during early adult life on ladybird reproductive performance (age at first reproduction and egg production). In this study, we investigated the effects of repeated reflex bleeding under various environmental contexts (resource availability) on basic haemolymph parameters and body mass change in the invasive ladybird Harmonia axyridis Pallas. However, the costs of reflex bleeding can also depend on the environmental context and physiological conditions of individuals 22. 22 showed no negative effect of repeated reflex bleeding on ladybird fitness (fecundity). On the other hand, a recent study by Lee et al. Sometimes, reflex bleeding can be linked to genetic costs 21. Species with external chemical defence can also be at a higher risk of parasitism by parasitoids 14, probably due to a weakened immune system. Reflex bleeding during the larval stage can result in reduced adult size or prolonged development time 9, 19, 20. The limited existing evidence indicates that not only nutrients but also other valuable components of haemolymph are lost during reflex bleeding, e.g., haemocytes and alkaloids 16, 17, 18. Nevertheless, the externalisation of haemolymph can pose a significant physiological cost to insects because some of their haemolymph is lost and needs to be replenished. In general, all types of externalised chemical defence seem to be efficient defensive strategies against various predators 14. The efficiency of reflex bleeding behaviour in insects has been confirmed against various predators, including small mammals, birds, lizards, and arthropods 3, 9, 13, 14, 15. In addition, several insect species from other orders employ alternative mechanisms to externalise the toxins in their body fluids to predators, such as easy bleeding in sawfly larvae 10 or regurgitation in lepidopterans, orthopterans, and others 11, 12. Reflex bleeding behaviour has been described, for example, for Plecoptera, Orthoptera, and Hemiptera 3, 4, 5, but it is most widespread in several beetle families, for example Meloidae, Erotylidae, Lampyridae, and Coccinellidae 6, 7, 8, 9. The release of haemolymph, when individuals are threatened or exposed to direct physical attack, is a common defensive behaviour in many insects with efficient toxins present in their bodies. Reflex bleeding (sometimes called “autohaemorrhaging”) is a well-known phenomenon which has fascinated biologists for centuries 1, 2. Overall, our results indicate that repeated reflex bleeding weakens a ladybird’s immune system and can increase their susceptibility to pathogens, but a ladybird’s reproductive potential remains almost unaffected, even by very intensive reflex bleeding. Moreover, ladybirds bleeding larger amounts of haemolymph started their reproduction significantly later. Daily reflex bleeding did not result in decreased fecundity of young ladybirds during the first 30 days of their adult life, but the start of ladybird reproduction was delayed by about two days. Interestingly, resource limitation in the form of complete food absence did not significantly interact with reflex bleeding, even though starvation itself had a strong negative effect on all haemolymph parameters investigated and individual body mass. Repeated reflex bleeding did not result in significant body mass reduction. Reflex bleeding induced twice a week for three weeks resulted in a significant reduction in haemocyte concentration, total protein content, and antimicrobial activity against Micrococcus luteus, and a marginally non-significant decrease in antimicrobial activity against Escherichia coli. In this study, we examined the immune and fitness costs of repeated reflex bleeding in adults of the invasive ladybird Harmonia axyridis, investigating several haemolymph parameters. Interestingly, this issue has rarely been investigated for adult insects. At the same time, significant costs of reflex bleeding can be expected because bled haemolymph is lost and all valuable components included have to be renewed. In insects, external chemical defences, such as reflex bleeding, have been proved to be an efficient strategy against various predators. ![]()
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