Biology subjects

Petschenka, G.

Publications and source records attributed to Petschenka, G..

10 recordsLinked to original sources

bioRxiv2025

Synergistic Enhancement of Acetamiprid Toxicity by Herbicide and Fungicide: Triple Mixture Outperforms Binary Combination

Pesticides are considered a major driver of insect decline, and non-target organisms in agricultural landscapes are frequently exposed to complex mixtures of agrochemicals. However, despite extensive research on mixture toxicity, most studies have predominantly focused on binary combinations, well-known synergistic interactions, and insecticide-fungicide mixtures, while other pesticide classes such as herbicides and higher-order mixtures remain underrepresented. In this study, we investigated the effects of binary and ternary combinations of representative active substances from three major pesticide classes: acetamiprid (insecticide), fluopyram (fungicide), and terbuthylazine (herbicide). We conducted acute contact dose-response assays on the non-target insect Oncopeltus fasciatus. While only acetamiprid showed acute toxicity when applied individually, its combination with terbuthylazine significantly increased toxicity, reducing the median effective dose (ED50) by a factor of 2.7. A similar, although not statistically significant, trend was observed for the combination with fluopyram. The mixture of all three compounds resulted in a marked increase in toxicity, exceeding the effects observed in any binary or single-substance treatment. These mixture effects deviate from classical additivity assumptions and can be interpreted as a potentiation of acetamiprid toxicity. While potential causes are discussed, the underlying mechanisms remain unclear. Our findings add to the growing body of evidence suggesting that non-additive effects beyond well-established pesticide combinations may occur more frequently than previously assumed. The pronounced response in the ternary mixture further indicates that higher-order mixtures may pose particular challenges for environmental risk assessment. Although this study follows a conceptual approach, the selected substances and concentrations are aligned with agricultural use patterns. Overall, our results highlight the potential for unexpected mixture effects across pesticide classes and emphasize the need to account for such interactions in environmental risk assessment.

ecology↗

bioRxiv2024

Double-stranded DNA reduces dsRNA degradation in the saliva and significantly enhanced RNAi-mediated gene silencing in Halyomorpha halys

The invasive pest Halyomorpha halys (Hemiptera: Pentatomidae) poses a significant threat to agriculture, necessitating effective control methods beyond chemical pesticides. Our research explores RNA interference (RNAi) as a targeted gene silencing approach for H. halys population management. However, the variable efficacy of RNAi across insect orders, particularly in hemipteran insects like H. halys, poses challenges. Ex vivo degradation assays revealed rapid degradation of double-stranded RNA (dsRNA) in H. halys (Hh) saliva and extracts of salivary glands across several growth stages, attributed to the high expression of the DNA/RNA non-specific nuclease (HhNSE). A key discovery from our research was that double-stranded DNA (dsDNA) can act as a protective agent, increasing the stability of dsRNA in saliva probably by competitive inhibition of HhNSE. Based on the well-established lethality of silencing the gene encoding the heavy chain of clathrin (HhCHC) in insects, this gene was chosen as a target to test the functionality of our dsDNA-based formulation for enhancing dsRNA-mediated gene silencing. Our in-vivo experiments showed increased HhCHC silencing after 72 hours of feeding initiation with a mixture of dsRNA-CHC and dsDNA, as opposed to dsRNA alone. This discovery indicates potential for enhancing the efficiency of orally delivered dsRNA through formulations based on dsDNA. Although the injection of dsRNA-CHC resulted in near-total mortality, the dsDNA formulation did not significantly enhance mortality rates when fed together with dsRNA-CHC. This emphasises the necessity for further investigation into additional factors beyond nuclease activity, such as the understanding of dsRNA uptake and release mechanisms within the gut epithelial cells of H. halys. Nevertheless, our study opens avenues for developing cost-effective formulations to enhance RNAi efficacy in H. halys and perhaps other insects where nucleases hinder dsRNA delivery, representing a promising solution for sustainable pest control. Graphical Abstract O_FIG O_LINKSMALLFIG WIDTH=200 HEIGHT=121 SRC="FIGDIR/small/617619v1_ufig1.gif" ALT="Figure 1"> View larger version (27K): org.highwire.dtl.DTLVardef@1517e13org.highwire.dtl.DTLVardef@12c4977org.highwire.dtl.DTLVardef@8b243borg.highwire.dtl.DTLVardef@f79eca_HPS_FORMAT_FIGEXP M_FIG C_FIG

molecular biology↗

bioRxiv2024

The neonicotinoid acetamiprid is highly toxic to wild non-target insects

Although pesticides are seen as one of the main drivers of insect decline, there are still only few studies that assess their effects on non-target species under field conditions. Here we investigated the effects of the neonicotinoid insecticide Mospilan(R)SG (active ingredient acetamiprid) on plant bugs (Heteroptera: Miridae), a dominant group of European grassland insect communities. Abundance of three focal mirid species was reduced by up to 78% two days after field exposure at concentrations expected at field margins, with mortality varying considerably among species. Follow-up feeding assays with insecticide-treated host plants in the greenhouse and controlled dose-response assays in the laboratory confirmed the strong negative effects on non-target species. Strikingly, the neonicotinoid was nearly 10,000 times more toxic to plant bugs than to honeybees. In addition, male bugs were 20 times more sensitive than females in two of the three tested species. Thus, continuous exposure to neonicotinoids in the field may reduce the plant bug populations and promote a shift towards more insecticide-tolerant species, altering community composition. We suggest that sex-specific sensitivity should be considered in risk assessment and conclude that the real risk to non-target insects is currently greatly underestimated.

ecology↗

bioRxiv2023

Monarchs sabotage milkweed to acquire toxins, not to disarm plant defence

Sabotaging milkweed by monarch caterpillars is a textbook example for disarming plant defence. By severing leaf veins, monarchs are thought to prevent toxic latex flow to their feeding site. Here we show that sabotaging by monarch caterpillars is not an avoidance strategy. Instead, caterpillars actively ingest outflowing latex to increase sequestration of toxic latex cardenolides. Comparisons with caterpillars of the related non-sequestering common crow butterfly revealed three lines of evidence supporting our hypothesis. First, monarchs sabotage inconsistently and therefore the behaviour is not mandatory to feed on milkweed, while sabotaging in crows precedes every feeding event. Second, monarchs eagerly drink latex, while crow caterpillars spit out latex during sabotaging. Third, monarchs raised on detached leaves sequestered more cardenolides when latex was supplemented artificially. Hence, we conclude, that monarchs converted the "sabotage to avoid" strategy of their relatives into a "sabotage to consume" strategy for acquiring toxins for defence.

ecology↗

bioRxiv2023

The path to "femmes fatales": the evolution of toxin resistance in predatory fireflies.

Toxic cardiotonic steroids (CTS) act as a defense mechanism in many firefly species (Lampyridae) by inhibiting a crucial enzyme called Na+,K+-ATPase (NKA). While most fireflies produce these toxins internally, species of the genus Photuris acquire them from a surprising source: predation on other fireflies. The contrasting physiology of toxin exposure and sequestration between Photuris and other firefly genera suggests that distinct strategies may be required to prevent self-intoxication. Our study demonstrates that both Photuris and their firefly prey have evolved highly-resistant NKAs. Using an evolutionary analysis of the specific target of CTS (ATP) in fireflies, and gene-editing in Drosophila, we find that the initial steps towards resistance were shared among Photuris and other firefly lineages. However, the Photuris lineage subsequently underwent multiple rounds of gene duplication and neofunctionalization, resulting in the development of ATP paralogs that are differentially expressed and exhibit increasing resistance to CTS. In contrast, other firefly species have maintained a single copy. Our results implicate gene duplication as a facilitator in the transition of Photuris to its distinct ecological role as predator of toxic firefly prey. One-Sentence SummaryGene duplication and neofunctionalization distinguish firefly predators from their toxic firefly prey.

evolutionary biology↗

bioRxiv2022

Spatial metabolomics reveal divergent cardenolide processing in the monarch butterfly (Danaus plexippus) and the common crow (Euploea core)

Although being famous for sequestering milkweed cardenolides, the mechanism of sequestration and where cardenolides are localized in caterpillars of the monarch butterfly (Danaus plexippus) is still unknown. While monarchs tolerate cardenolides by a resistant Na+/K+-ATPase, it is unclear how closely related species such as the non-sequestering common crow (Euploea core) cope with these toxins. Using novel atmospheric-pressure scanning microprobe matrix-assisted laser/desorption ionization mass spectrometry imaging, we compared the distribution of cardenolides in caterpillars of D. plexippus and E. core. Specifically, we tested at which physiological scale quantitative differences between both species are mediated and how cardenolides distribute across body tissues. Whereas D. plexippus sequestered most cardenolides from milkweed (Asclepias curassavica), no cardenolides were found in the tissues of E. core. Remarkably, quantitative differences already manifest in the gut lumen: while monarchs retain and accumulate cardenolides above plant concentrations, the toxins are degraded in the gut lumen of crows. We visualized cardenolide transport over the monarch midgut epithelium and identified integument cells as the final site of storage where defenses might be perceived by predators. Our study provides molecular insight into cardenolide sequestration and highlights the great potential of mass spectrometry imaging for understanding the kinetics of multiple compounds including endogenous metabolites, plant toxins, or insecticides in insects.

ecology↗

bioRxiv2021

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

O_LISequestration, 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. C_LIO_LIMilkweed 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. C_LIO_LIUsing 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. C_LIO_LIWe 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. C_LIO_LIWe 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. C_LI

ecology↗

bioRxiv2020

Predation drives specialized host plant associations in preadapted milkweed bugs (Heteroptera: Lygaeinae)

Host plant specialization across herbivorous insects varies dramatically, but the underlying evolutionary mechanisms are little-known. The milkweed bugs (Heteroptera: Lygaeinae) are ancestrally associated with plants of the Apocynaceae from which they commonly sequester cardiac glycosides for defense, facilitated by resistant Na+/K+-ATPases and adaptations for transport, storage and discharge of toxins. Here, we show that three Lygaeinae species independently colonized four novel non-apocynaceous hosts, convergently producing cardiac glycosides. A fourth species shifted to a new source of toxins by tolerating and sequestering alkaloids from meadow saffron (Colchicum autumnale, Colchicaceae). Across three species tested, feeding on seeds containing toxins did not improve growth, but sequestration mediated protection against predatory lacewing larvae and birds. We conclude that physiological preadaptations and convergent phytochemistry facilitated novel specialized host associations. Therefore, selection by predators on sequestration of defenses, rather than the exploitation of novel dietary resources, can lead to obligatory specialized host associations in generalist insects.

evolutionary biology↗

bioRxiv2019

Rapid and independent evolution of ancestral and novel defenses in a genus of toxic plants (Erysimum, Brassicaceae)

Phytochemical diversity is thought to result from coevolutionary cycles as specialization in herbivores imposes diversifying selection on plant chemical defenses. Plants in the speciose genus Erysimum (Brassicaceae) produce both ancestral glucosinolates and evolutionarily novel cardenolides as defenses. Here we test macroevolutionary hypotheses on co-expression, co-regulation, and diversification of these potentially redundant defenses across this genus. We sequenced and assembled the genome of E. cheiranthoides and foliar transcriptomes of 47 additional Erysimum species to construct a highly resolved phylogeny, revealing that cardenolide diversity increased rapidly rather than gradually over evolutionary time. Concentrations, inducibility, and diversity of the two defenses varied independently among species, with no evidence for trade-offs. Closely related species shared similar cardenolide traits, but not glucosinolate traits, likely as a result of specific selective pressures acting on distinct molecular diversification mechanisms. Ancestral and novel chemical defenses in Erysimum thus appear to provide complementary rather than redundant functions.

plant biology↗

bioRxiv2019

Adaptive substitutions underlying cardiac glycoside insensitivity in insects exhibit epistasis in vivo.

Predicting how species will respond to selection pressures requires understanding the factors that constrain their evolution. We use genome engineering of Drosophila to investigate constraints on the repeated evolution of unrelated herbivorous insects to toxic cardiac glycosides, which primarily occurs via a small subset of possible functionally-relevant substitutions to Na+,K+-ATPase. Surprisingly, we find that frequently observed adaptive substitutions at two sites, 111 and 122, are lethal when homozygous and adult heterozygotes exhibit dominant neural dysfunction. We identify a phylogenetically correlated substitution, A119S, that partially ameliorates the deleterious effects of substitutions at 111 and 122. Despite contributing little to cardiac glycoside-insensitivity in vitro, A119S, like substitutions at 111 and 122, substantially increases adult survivorship upon cardiac glycoside exposure. Our results demonstrate the importance of epistasis in constraining adaptive paths. Moreover, by revealing distinct effects of substitutions in vitro and in vivo, our results underscore the importance of evaluating the fitness of adaptive substitutions and their interactions in whole organisms.

evolutionary biology↗