Biparental endowment of endogenous defensive alkaloids in Epilachna paenulata

Intraspecific Variation in the Alkaloids of Adalia decempunctata (Coleoptera, Coccinellidae): Sex, Reproduction and Colour Pattern Polymorphism

In this paper, we examine intraspecific variation in the quantity of alkaloid chemical defence in field collected individuals of the polymorphic ladybird beetle Adalia decempunctata (10-spot ladybird). Like its more widely studied relative Adalia bipunctata (2-spot ladybird), A. decempunctata possesses the alkaloids adaline and adalinine, which are, respectively, the major and minor alkaloids of A. bipunctata. We focused especially on alkaloid concentration in relation to colour pattern morph, sex, and the relationship between female and egg parameters. There was a marked sexual dimorphism in the balance of the two alkaloids, with adaline predominating in females and adalinine predominating in males: in males, on average, over 70% of total alkaloid was adalinine. Females had a lower proportion of adalinine (< 10%) than their eggs (> 15%) and relationships between egg alkaloid and female alkaloid or fecundity were weak or non-existent. Colour pattern morph had a borderline (although not) significant relationship with adaline concentration and total alkaloid concentration, which could be further explored with laboratory reared individuals. The sexual dimorphism in alkaloid content, which seems likely due to differences in synthesis, might be related to their relative costs to the two sexes and might provide insight into the evolution of alkaloid diversity in ladybirds.

Egg toxic compounds in the animal kingdom. A comprehensive review

Covering: 1951 to 2022Packed with nutrients and unable to escape, eggs are the most vulnerable stage of an animal's life cycle. Consequently, many species have evolved chemical defenses and teamed up their eggs with a vast array of toxic molecules for defense against predators, parasites, or pathogens. However, studies on egg toxins are rather scarce and the available information is scattered. The aim of this review is to provide an overview of animal egg toxins and to analyze the trends and patterns with respect to the chemistry and biosynthesis of these toxins. We analyzed their ecology, distribution, sources, occurrence, structure, function, relative toxicity, and mechanistic aspects and include a brief section on the aposematic coloration of toxic eggs. We propose criteria for a multiparametric classification that accounts for the complexity of analyzing the full set of toxins of animal eggs. Around 100 properly identified egg toxins are found in 188 species, distributed in 5 phyla: cnidarians (2) platyhelminths (2), mollusks (9), arthropods (125), and chordates (50). Their scattered pattern among animals suggests that species have evolved this strategy independently on numerous occasions. Alkaloids are the most abundant and widespread, among the 13 types of egg toxins recognized. Egg toxins are derived directly from the environment or are endogenously synthesized, and most of them are transferred by females inside the eggs. Their toxicity ranges from ρmol kg^-1 to mmol kg^-1, and for some species, experiments support their role in predation deterrence. There is still a huge gap in information to complete the whole picture of this field and the number of toxic eggs seems largely underestimated.

Chemical defense acquired via pharmacophagy can lead to protection from predation for conspecifics in a sawfly

Chemical defense is a widespread anti-predator strategy exhibited by organisms, with individuals either synthesizing or extrinsically acquiring defensive chemicals. In some species, such defences can also be transferred among conspecifics. Here, we tested the effects of pharmacophagy on the defense capability of the turnip sawfly, Athalia rosae, which can acquire neo-clerodane diterpenoids (clerodanoids) via pharmacophagy when having access to the plant Ajuga reptans. We show that clerodanoid access mediates protection against predation by mantids for the sawflies, both in a no-choice feeding assay and a microcosm setup. Even indirect access to clerodanoids, via nibbling on conspecifics that had access to the plant, resulted in protection against predation albeit to a lower degree than direct access. Furthermore, sawflies that had no direct access to clerodanoids were consumed less frequently by mantids when they were grouped with conspecifics that had direct access. Most, but not all, of such initially undefended sawflies could acquire clerodanoids from conspecifics that had direct access to the plant, although in low quantities. Together our results demonstrate that clerodanoids serve as a chemical defense that can also be transferred by interactions among conspecifics. Moreover, the presence of chemically defended individuals in a group can confer protection onto conspecifics that had no direct access to clerodanoids.

Phenolic Fingerprinting, Antioxidant, and Deterrent Potentials of Persicaria maculosa Extracts

Persicaria maculosa (Polygonaceae) (known as lady’s thumb) is an annual morphologically variable weed that is widely distributed in Chile. The purpose of this study was to investigate the antifeedant potential of methanolic (MeOH), ethanolic (EtOH), and dichloromethane (DCM) extracts from the aerial parts of this plant collected in the Valparaíso and Curicó provinces (Chile) and relate this activity to the antioxidant capacity and the presence of phenolic compounds in the extracts. A phenolic profile based on HPLC-ESI-MS/MS allowed the identification of 26 phenolic compounds, most of them glycosyl derivatives of isorhamnetin, quercetin, and kaempferol. In addition, the total phenolic content (TP), total flavonoids (TF), and antioxidant activity measured by 2,2-diphenyl-1-picrylhydrazyl (DPPH), superoxide anion scavenging (O₂⁻), ferric-reducing antioxidant power (FRAP), and cupric-reducing antioxidant capacity (CUPRAC) of the extracts are reported. The antifeedant potentials of the plant extracts were tested against Epilachna paenulata, Pseudaletia adultera, Macrosiphum euphorbiae, and Diaphorina citri insects for the first time. The activity against the aphid M. euphorbiae was significant for the DCM extracts of plants from Valparaíso and Curicó (settling % = 23% ± 4% and 23% ± 5%, respectively). The antifeedant activities against the beetle E. paenulata and the lepidoptera P. adultera were significant for Valparaíso extracts, especially when tested against E. Paenulata (IFP = 1.0 ± 0.0). Finally, the MeOH and EtOH extracts from Valparaíso plants reduced the diet consumption of the psilid D. citri (p < 0.05). The results showed that P. maculosa is a good source of flavonoids with some antioxidant capacities and has potential interest as botanical eco-friendly alternative with deterrent activity.

Intragroup and intragenomic conflict over chemical defense against predators

Insects are often chemically defended against predators. There is considerable evidence for a group-beneficial element to their defenses, and an associated potential for individuals to curtail their own investment in costly defense while benefitting from the investments of others, termed "automimicry." Although females in chemically defended taxa often lay their eggs in clusters, leading to siblings living in close proximity, current models of automimicry have neglected kin-selection effects, which may be expected to curb the evolution of such selfishness. Here, we develop a general theory of automimicry that explicitly incorporates kin selection. We investigate how female promiscuity modulates intragroup and intragenomic conflicts overinvestment into chemical defense, finding that individuals are favored to invest less than is optimal for their group, and that maternal-origin genes favor greater investment than do paternal-origin genes. We translate these conflicts into readily testable predictions concerning gene expression patterns and the phenotypic consequences of genomic perturbations, and discuss how our results may inform gene discovery in relation to economically important agricultural products.

Sexual activity diminishes male virility in two Coccinella species: consequences for female fertility and progeny development

Male contributions, both chemical and behavioural, can influence female sperm usage and reproductive success. To determine whether such male factors are subject to depletion in Coccinella septempunctata and Coccinella transversalis, we tested the effects of male mating history on male virility, as estimated by measures of mating behaviour, female reproductive success and progeny fitness, with parental age held constant. Overt measures of male mating effort (wriggling duration, number of shaking bouts and total copula duration) all diminished from virgin to 5×mated males and were mirrored by concurrent declines in female fecundity and fertility(measured over 20 days). Paternal effects were also observed which diminished as a function of mating history, suggesting that transgenerational signals of male origin are also subject to depletion. Progeny of virgin fathers had higher rates of survival(C. transversalis) and faster development (both species) than progeny of 5×mated fathers. Seminal fluid proteins are known to have allohormonal properties and can stimulate female fecundity and fertility in a number of insects, making them strong candidates for depletion as a function of mating activity. However, it is also possible that sperm limitation and/or reduced tactile stimulation of females by multiple-mated males may have contributed to some of the observed effects.

Origin of Epilachnapaenulata defensive alkaloids: incorporation of [1-13C]-sodium acetate and [methyl-2H3]-stearic acid

Ladybird beetles produce a large number of defensive alkaloids. Previous studies suggest that the structural diversity of these endogenous alkaloids can be traced to a common biosynthetic route based on the condensation of several acetate units. In this study, adults of Epilachna paenulata, a phytophagous neotropical species, were fed on diet enriched with potential precursors (sodium acetate, fatty acids and the amino acids lysine and ornithine) labeled with stable isotopes ((13)C, (2)H and (15)N). Labeled acetate was incorporated into the structurally related homotropane and piperidine alkaloids. The later also showed incorporation of [methyl-(2)H3] stearic acid. Our results hence support a fatty acid pathway for the biosynthesis of E. paenulata alkaloids. To our knowledge, this is the first report on the incorporation of a labeled fatty acid into a defensive piperidine alkaloid in insects.

Response of Epilachna paenulata to two flavonoids, pinocembrin and quercetin, in a comparative study

We examined the effects of the flavonoids pinocembrin and quercetin on the feeding behavior, survival, and development of the Cucurbitaceae pest Epilachna paenulata (Coleoptera: Coccinellidae). In no-choice experiments, 48 hr-consumption of Cucurbita maxima Duch. leaves treated with pinocembrin at 1, 5, and 50 microg/cm(2) was less than one third of that for leaves treated with 0.1 microg/cm(2) of pinocembrin or untreated leaves. Larvae stopped feeding after 9 days of high doses of pinocembrin (5 and 50 microg/cm(2)), and larval weight and survival were negatively affected by pinocembrin at 1-50 microg/cm(2). Delayed mortality in comparison to food-deprived larvae suggests that the mechanism of action for pinocembrin is chronic intoxication, rather than simple starvation from antifeedant effects. In contrast, leaf consumption and larval weight were not significantly affected by quercetin (at 0.1, 1, 5, and 50 microg/cm(2)) while mortality rates were only slightly increased. The response of E. paenulata larvae in a choice-test to combinations of pinocembrin at antifeedant doses (5 and 50 microg/cm(2)) and quercetin at phagostimulant doses (0.01 and 0.1 microg/cm(2)) indicated that the feeding deterrent activity of the former completely overshadowed the stimulant activity of the latter. These results demonstrate the different responses of one insect species to two widely distributed plant flavonoids. Pinocembrin strongly affected survival of E. paenulata while quercetin had only a weak effect without major consequences on the insect life-cycle.