Food stress prompts dispersal behavior in apterous pea aphids: do activated aphids incur energy loss?

Dispersal stabilizes coupled ecological and evolutionary dynamics in a host-parasitoid system

When ecological and evolutionary dynamics occur on comparable timescales, persistence of the ensuing eco-evolutionary dynamics requires both ecological and evolutionary stability. This unites key questions in ecology and evolution: How do species coexist, and what maintains genetic variation in a population? In this work, we investigated a host-parasitoid system in which pea aphid hosts rapidly evolve resistance to Aphidius ervi parasitoids. Field data and mathematical simulations showed that heterogeneity in parasitoid dispersal can generate variation in parasitism-mediated selection on hosts through time and space. Experiments showed how evolutionary trade-offs plus moderate host dispersal across this selection mosaic cause host-parasitoid coexistence and maintenance of genetic variation in host resistance. Our results show how dispersal can stabilize both the ecological and evolutionary components of eco-evolutionary dynamics.

Mixed insect pest populations of Diaspididae species under control of oligonucleotide insecticides: 3'-end nucleotide matters

Diaspididae are one of the most serious small herbivorous insects with piercing-sucking mouth parts and are major economic pests as they attack and destroy perennial ornamentals and food crops. Chemical control is the primary management approach for armored scale infestation. However, chemical insecticides do not possess selectivity in action and not always effective enough for the control of armored scale insects. Our previous work showed that green oligonucleotide insecticides (olinscides) are highly effective against armored and soft scale insects. Moreover, olinscides possess affordability, selectivity in action, fast biodegradability, and a low carbon footprint. Insect pest populations undergo microevolution and olinscides should take into account the problem of insecticide resistance. Using sequencing results, it was found that in the mixed populations of insect pests Dynaspidiotus britannicus Newstead and Aonidia lauri Bouche, predominates the population of A. lauri. Individuals of A. lauri comprised for 80% of individuals with the sequence 3'-ATC-GTT-GGC-AT-5' in the 28S rRNA site, and 20% of the population comprised D. britannicus individuals with the sequence 3'-ATC-GTC-GGT-AT-5'. We created olinscides Diasp80-11 (5'-ATG-CCA-ACG-AT-3') and Diasp20-11 (5'-ATA-CCG-ACG-AT-3') with perfect complementarity to each of the sequences. Mortality of insects on the 14th day comprised 98.19 ± 3.12% in Diasp80-11 group, 64.66 ± 0.67% in Diasp20-11 group (p < 0.05), and 3.77 ± 0.94% in the control group. Results indicate that for maximum insecticidal effect it is necessary to use an oligonucleotide insecticide that corresponds to the dominant species. Mortality in Diasp80-11 group was accompanied with significant decrease in target 28S rRNA concentration and was 8.44 ± 0.14 and 1.72 ± 0.36 times lower in comparison with control (p < 0.05) on the 10th and 14th days, respectively. We decided to make single nucleotide substitutions in Diasp20-11 olinscide to understand which nucleotide will play the most important role in insecticidal effect. We created three sequences with single nucleotide transversion substitutions at the 5'-end - Diasp20(5')-11 (A to T), 3'-end - Diasp20(3')-11 (T to A), and in the middle of the sequence - Diasp20(6)-11 (6th nitrogenous base of the sequence; G to C), respectively. As a result, mortality of mixed population of the field experiment decreased and comprised 53.89 ± 7.25% in Diasp20(5')-11 group, 40.68 ± 4.33% in Diasp20(6)-11 group, 35.74 ± 5.51% in Diasp20(3')-11 group, and 3.77 ± 0.94% in the control group on the 14th day. Thus, complementarity of the 3'-end nucleotide to target 28S rRNA was the most important for pronounced insecticidal effect (significance of complementarity of nucleotides for insecticidal effect: 5' nt < 6 nt < 3' nt). As was found in our previous research works, the most important rule to obtain maximum insecticidal effect is complete complementarity to the target rRNA sequence and maximum coverage of target sequence in insect pest populations. However, in this article we also show that the complementarity of 3'-end is a second important factor for insecticidal potential of olinscides. Also in this article we propose 2-step DNA containment mechanism of action of olinscides, recruiting RNase H. The data obtained indicate the selectivity of olinscides and at the same time provide a simple and flexible platform for the creation of effective plant protection products, based on antisense DNA oligonucleotides.

Identification of azukisapogenol triterpenoid saponins from Oxytropis hirta Bunge and their aphicidal activities against pea aphid Acyrthosiphon pisum Harris

BACKGROUND

Acyrthosiphon pisum Harris is the most destructive pest worldwide because of its ability to feed on plants directly and transmit plant viruses as a vector. This study aims to identify triterpenoid saponins from Oxytropis hirta Bunge as biopesticides to control aphids.

RESULTS

Three new azukisapogenol triterpenoid saponins (1-3), a new pinoresinol lignan glycoside (8), and four known saponins (4-7) were identified from the root of O. hirta. Compounds 4-7 displayed significant aphicidal activities against A. pisum with oral toxicities (LC₅₀  = 51.10-147.43 μg/mL, 72 h), deterrent effects (deterrence index = 1.00, 100-200 μg/mL, 24 h), and aphid reproduction inhibitory effects (inhibition rates = 75.91-86.73%, 400 μg/mL, 24 h), respectively. The carboxyl groups at C-3 GlcA and C-30 were functional groups for their aphicidal activities. The toxic symptoms caused by the optimal 5 involved insect body-color changes from light green to dark or gray-green, and then brown until death. The intestinal cavity, apical microvilli, nuclei, mitochondria, and electron dense granules in the midgut tissues of A. pisum were the target sites showing aphicidal activity. The suppression of pepsin and α-amylase, and the activation of lipase and trypsin could be the signs of organelle damage in the midgut tissues.

CONCLUSION

Azukisapogenol triterpenoid saponins from O. hirta could be used as biopesticides to control aphids for their multiple efficacies, including oral toxicity, deterrent activity, and reproduction inhibitory activity. The toxic symptoms involved insect body-color changes. Midgut tissues and their related enzymes were the targets for saponins showing aphicidal activities. © 2022 Society of Chemical Industry.

Fight or Flight? Alternative Defense of the Pea Aphids, Acyrthosiphon pisum on Different Host Plants

Simple Summary

In the event of a pathogen attack, fecundity compensation and production of winged offspring are critical in pea aphids. However, little is known about the effects of the host plant on these responses. The purpose of this study was to investigate the effects of host plant on these two alternative defenses in pea aphids. We took a single adult female from a pink colony of pea aphids that was originally from broad beans and allowed her to reproduce offspring in the laboratory. Some offspring were fed broad beans, while others were fed alfalfa for over 30 generations. We first investigated the backgrounds of their facultative symbionts before infecting them with pathogens and found that the composition of secondary symbionts in our aphid colony was not affected by the host plants. Broad bean reared pea aphids produced more offspring in infected and uninfected conditions, whereas alfalfa reared pea aphids produced more winged offspring when confronting challenges caused by Staphylococcus aureus and Beauveria bassiana. Our findings showed that the host plant influences the pea aphid’s alternative responses to mortality risks.

Abstract

Non-immunological responses are important alternative strategies for animals to deal with pathogens. It has long been recognized that fecundity compensation and production of winged offspring are two common non-immunological responses used by aphids when confronted with predators or pathogens. However, the effects of host plant on these responses have received little attention. This study investigated the effects of host plant on non-immunological defense in the pea aphids, Acyrthosiphon pisum, after bacterial and fungal infections. The aphids were raised in two groups, with one group being raised on broad beans and the other group being raised on alfalfa. The secondary symbiont background was examined, and the aphids were then infected with bacteria and fungus to assess fecundity and winged offspring production. We found that aphids that had been fed alfalfa had fewer offspring than those fed broad beans. Alfalfa-fed aphids produced more winged offspring in response to S. aureus and B. bassiana infections. Our findings suggest that the host plant plays a key role in fecundity and winged offspring production in pea aphid colony.

The physiology of movement

Movement, from foraging to migration, is known to be under the influence of the environment. The translation of environmental cues to individual movement decision making is determined by an individual's internal state and anticipated to balance costs and benefits. General body condition, metabolic and hormonal physiology mechanistically underpin this internal state. These physiological determinants are tightly, and often genetically linked with each other and hence central to a mechanistic understanding of movement. We here synthesise the available evidence of the physiological drivers and signatures of movement and review (1) how physiological state as measured in its most coarse way by body condition correlates with movement decisions during foraging, migration and dispersal, (2) how hormonal changes underlie changes in these movement strategies and (3) how these can be linked to molecular pathways. We reveale that a high body condition facilitates the efficiency of routine foraging, dispersal and migration. Dispersal decision making is, however, in some cases stimulated by a decreased individual condition. Many of the biotic and abiotic stressors that induce movement initiate a physiological cascade in vertebrates through the production of stress hormones. Movement is therefore associated with hormone levels in vertebrates but also insects, often in interaction with factors related to body or social condition. The underlying molecular and physiological mechanisms are currently studied in few model species, and show -in congruence with our insights on the role of body condition- a central role of energy metabolism during glycolysis, and the coupling with timing processes during migration. Molecular insights into the physiological basis of movement remain, however, highly refractory. We finalise this review with a critical reflection on the importance of these physiological feedbacks for a better mechanistic understanding of movement and its effects on ecological dynamics at all levels of biological organization.

Starvation Stress Causes Body Color Change and Pigment Degradation in Acyrthosiphon pisum

The pea aphid, Acyrthosiphon pisum (Harris), shows body color shifting from red to pale under starvation in laboratory conditions. These body color changes reflect aphid’s adaptation to environmental stress. To understand the color-shifting patterns, the underlying mechanism and its biological or ecological functions, we measured the process of A. pisum’s body color shifting patterns using a digital imagery and analysis system; we conducted a series of biochemical experiments to determine the mechanism that causes color change and performed biochemical and molecular analyses of the energy reserves during the color shifting process. We found that the red morph of A. pisum could shift their body color to pale red, when starved; this change occurred rapidly at a certain stress threshold. Once A. pisum initiated the process, the shifting could not be stopped or reversed even after food was re-introduced. We also discovered that the orange-red pigments may be responsible for the color shift and that the shift might be caused by the degradation of these pigments. The carbohydrate and lipid content correlated to the fading of color in red A. pisum. A comparative analysis revealed that these reddish pigments might be used as backup energy. The fading of color reflects a reorganization of the energy reserves under nutritional stress in A. pisum; surprisingly, aphids with different body colors exhibit diverse strategies for storage and consumption of energy reserves.

A β-carotene-binding protein carrying a red pigment regulates body-color transition between green and black in locusts

Changes of body color have important effects for animals in adapting to variable environments. The migratory locust exhibits body color polyphenism between solitary and gregarious individuals, with the former displaying a uniform green coloration and the latter having a prominent pattern of black dorsal and brown ventral surface. However, the molecular mechanism underlying the density-dependent body color changes of conspecific locusts remain largely unknown. Here, we found that upregulation of β-carotene-binding protein promotes the accumulation of red pigment, which added to the green color palette present in solitary locusts changes it from green to black, and that downregulation of this protein led to the reverse, changing the color of gregarious locusts from black to green. Our results provide insight that color changes of locusts are dependent on variation in the red β-carotene pigment binding to βCBP. This finding of animal coloration corresponds with trichromatic theory of color vision.

How symbiosis and ecological context influence the variable expression of transgenerational wing induction upon fungal infection of aphids

Aphids, like most animals, mount a diverse set of defenses against pathogens. For aphids, two of the best studied defenses are symbiont-conferred protection and transgenerational wing induction. Aphids can harbor bacterial symbionts that provide protection against pathogens, parasitoids and predators, as well as against other environmental stressors. In response to signals of danger, aphids also protect not themselves but their offspring by producing more winged than unwinged offspring as a way to ensure that their progeny may be able to escape deteriorating conditions. Such transgenerational wing induction has been studied most commonly as a response to overcrowding of host plants and presence of predators, but recent evidence suggests that pea aphids (Acyrthosiphon pisum) may also begin to produce a greater proportion of winged offspring when infected with fungal pathogens. Here, we explore this phenomenon further by asking how protective symbionts, pathogen dosage and environmental conditions influence this response. Overall, while we find some evidence that protective symbionts can modulate transgenerational wing induction in response to fungal pathogens, we observe that transgenerational wing induction in response to fungal infection is highly variable. That variability cannot be explained entirely by symbiont association, by pathogen load or by environmental stress, leaving the possibility that a complex interplay of genotypic and environmental factors may together influence this trait.

Strategies used by two apterous strains of the pea aphid Acyrthosiphon pisum for passive dispersal

Wingless forms of aphids are relatively sedentary, and have a limited ability to migrate or disperse. However, they can drop off hosts or walk away if disturbed, or their food quality or quantity become deteriorated. Earlier, we found that the pea aphid, Acyrthosiphon pisum (Harris, 1776), could use differed strategies to escape danger and locate new host plants. To determine the mechanisms behind the different strategies, we undertook a series of studies including the aphids' host location, energy reserves under starvation, glycogenesis, sugar assimilation, olfactory and probing behaviors. We found that in our controlled laboratory conditions, one strain (local laboratory strain) moved longer distances and dispersed wider ranges, and correspondingly these aphids assimilated more sugars, synthesized more glycogen, and moved faster than another strain (collected from Gansu Province, northwestern China). However, the latter strain could locate the host faster, probed leaves more frequently, and identified plant leaves more accurately than the former strain after they were starved. Our results explained how flightless or wingless insects adapt to fit biotic and abiotic challenges in the complex processes of natural selection.

Environment exploration and colonization behavior of the pea aphid associated with the expression of the foraging gene

Aphids respond to specific environmental cues by producing alternative morphs, a phenomenon called polyphenism, but also by modulating their individual behavior even within the same morph. This complex plasticity allows a rapid adaptation of individuals to fluctuating environmental conditions, but the underlying genetic and molecular mechanisms remain largely unknown. The foraging gene is known to be associated with behavior in various species and has been shown to mediate the behavioral shift induced by environmental changes in some insects. In this study, we investigated the function of this gene in the clonal forms of the pea aphid Acyrthosiphon pisum by identifying and cloning cDNA variants, as well as analyzing their expression levels in developmental morphs and behavioral variants. Our results indicate that the expression of foraging changes at key steps of the aphid development. This gene is also highly expressed in sedentary wingless adult morphs reared under crowded conditions, probably just before they start walking and foraging. The cGMP-dependent protein kinase (PKG) enzyme activity measured in the behavioral variants correlates with the level of foraging expression. Altogether, our results suggest that foraging could act to promote the shift from a sedentary to an exploratory behavior, being thus involved in the behavioral plasticity of the pea aphid.