Cryptochrome-dependent magnetoreception in heteropteran insect continues even after 24 hours in darkness

Sensitivity to magnetic fields is dependent on the intensity and color of light in several animal species. The of light-dependent magnetoreception working model points to Cryptochrome (Cry) as a protein able to cooperate with its cofactor flavin, which possibly becomes a magnetically susceptible pair upon excitation by light. What type of Cry is involved as well as what pair of magnetosensitive radicals are responsible is still elusive. Therefore, we developed a conditioning assay for the firebug (the firebug) Pyrrhocoris apterus, an insect species that possesses only the mammalian Cryptochrome (Cry II). Here, using the engineered Cry II null mutant, we show that: i) vertebrate-like Cry II is an essential component of the magnetoreception response, and ii) magnetic conditioning continues even after 25 hours in darkness. The light-dependent and dark-persisting magnetoreception based on Cry II may inspire new perspectives in magnetoreception and Cryptochrome research.

The arrival and spread of the European firebug Pyrrhocoris apterus in Australia as documented by citizen scientists

We present evidence of the recent introduction and quick spread of the European firebug Pyrrhocoris apterus in Australia, as documented on the citizen science platform iNaturalist. The first public record of the species was reported in December 2018 in the City of Brimbank (Melbourne, Victoria). Since then, the species distribution has quickly expanded into 15 local government areas surrounding this first observation, including areas in both Metropolitan Melbourne and regional Victoria. The number of records of the European firebug in Victoria has also seen a substantial increase, with a current tally of almost 100 observations in iNaturalist as of July 31st, 2021. The case of the European firebug in Australia adds to the list of examples of citizen scientists playing a key role in not only early detection of newly introduced species but in documenting their expansion across their non-native range. Citizen science presents an exciting opportunity to complement biosecurity efforts carried out by government agencies, which often lack resources to sufficiently fund detection and monitoring programs given the overwhelming number of current and potential invasive species. Recognising and supporting the invaluable contribution of citizen scientists to science and society can help reduce this gap by: (1) increasing the number of introduced species that are quickly detected; (2) gathering evidence of the species’ early expansion stage; and (3) prompting adequate monitoring and rapid management plans for potentially harmful species.Given the range expansion patterns of the European firebug worldwide, their adaptation ability, and future climate scenarios, we suspect this species will continue expanding beyond Victoria, including other parts of Australia, New Zealand, and the South Pacific. We firmly believe that most of the knowledge about how this expansion process continues to happen will be provided by citizen scientists.

Dietary cardenolides enhance growth and change the direction of the fecundity-longevity trade-off in milkweed bugs (Heteroptera: Lygaeinae)

1. Sequestration, i.e., the accumulation of plant toxins into body tissues for defence, is primarily observed in specialised insects. Sequestration was frequently predicted to incur a physiological cost mediated by increased exposure to plant toxins and may require resistance traits different from those of non-sequestering insects. Alternatively, sequestering species could experience a cost in the absence of toxins due to selection on physiological homeostasis under permanent exposure of sequestered toxins in body tissues. 2. Milkweed bugs (Heteroptera: Lygaeinae) sequester high amounts of plant-derived cardenolides. Although being potent inhibitors of the ubiquitous animal enzyme Na+/K+-ATPase, milkweed bugs can tolerate cardenolides by means of resistant Na+/K+-ATPases. Both adaptations, resistance and sequestration, are ancestral traits shared by most species of the Lygaeinae. 3. Using four milkweed bug species and the related European firebug (Pyrrhocoris apterus) showing different combinations of the traits ′cardenolide resistance′ and ′cardenolide sequestration′, we set out to test how the two traits affect larval growth upon exposure to dietary cardenolides in an artificial diet system. While cardenolides impaired the growth of P. apterus nymphs neither possessing a resistant Na+/K+-ATPase nor sequestering cardenolides, growth was not affected in the non-sequestering milkweed bug Arocatus longiceps, which possesses a resistant Na+/K+-ATPase. Remarkably, cardenolides increased growth in the sequestering dietary specialists Caenocoris nerii and Oncopeltus fasciatus but not in the sequestering dietary generalist Spilostethus pandurus, which all possess a resistant Na+/K+-ATPase. 4. We then assessed the effect of dietary cardenolides on additional life history parameters, including developmental speed, the longevity of adults, and reproductive success in O. fasciatus. Remarkably, nymphs under cardenolide exposure developed substantially faster and lived longer as adults. However, fecundity of adults was reduced when maintained on cardenolide-containing diet for their entire life-time but not when adults were transferred to non-toxic sunflower seeds. 5. We speculate that the resistant Na+/K+-ATPase of milkweed bugs is selected for working optimally in a ′toxic environment′, i.e. when sequestered cardenolides are stored in the body tissues. Contrary to the assumption that toxins sequestered for defence produce a physiological burden, our data suggest that they can even increase fitness in specialised insects.

Adipokinetic Hormones Enhance the Efficacy of the Entomopathogenic Fungus Isaria fumosorosea in Model and Pest Insects

Insect adipokinetic hormones (AKHs) are neuropeptides with a wide range of actions, including the control of insect energy metabolism. These hormones are also known to be involved in the insect defence system against toxins and pathogens. In this study, our aim was to demonstrate whether the application of external AKHs significantly enhances the efficacy of the entomopathogenic fungus Isaria fumosorosea in a model species (firebug Pyrrhocoris apterus) and pest species (Egyptian cotton leafworm Spodoptera littoralis and pea aphid Acyrthosiphon pisum). It was found that the co-application of Isaria with AKHs significantly enhanced insect mortality in comparison to the application of Isaria alone. The mode of action probably involves an increase in metabolism that is caused by AKHs (evidenced by the production of carbon dioxide), which accelerates the turnover of Isaria toxins produced into the infected insects. However, several species-specific differences probably exist. Intoxication by Isaria elicited the stimulation of Akh gene expression and synthesis of AKHs. Therefore, all interactions between Isaria and AKH actions as well as their impact on insect physiology from a theoretical and practical point of view need to be discussed further.