Assessing immunocompetence in red palm weevil adult and immature stages in response to bacterial challenge and entomopathogenic nematode infection

Parasites and pathogens can follow different patterns of infection depending on the host developmental stage or sex. In fact, immune function is energetically costly for hosts and trade‐offs exist between immune defenses and life history traits as growth, development and reproduction and organisms should thus optimize immune defense through their life cycle according to their developmental stage. Identifying the most susceptible target and the most virulent pathogen is particularly important in the case of insect pests, in order to develop effective control strategies targeting the most vulnerable individuals with the most effective control agent. Here, we carried out laboratory tests to identify the most susceptible target of infection by infecting different stages of the red palm weevil Rhynchophorus ferrugineus (larvae, pupae, male, and female adults) with both a generic pathogen, antibiotic‐resistant Gram‐negative bacteria Escherichia coli XL1‐Blue, and two specific strains of entomopathogenic nematodes (EPNs), Steinernema carpocapsae ItS‐CAO1 and Heterorhabditis bacteriophora ItH‐LU1. By evaluating bacterial clearance, host mortality and parasite progeny release, we demonstrate that larvae are more resistant than adults to bacterial challenge and they release less EPNs progeny after infection despite a higher mortality compared to adults. Considering the two EPN strains, S. carpocapsae was more virulent than H. bacteriophora both in terms of host mortality and more abundant progeny released by hosts after death. The outcomes attained with unspecific and specific pathogens provide useful information for a more efficient and sustainable management of this invasive pest.     

The trade‐off to macroptery in the cricket Gryllus firmus: a path analysis in males

Among the Orthoptera, wing dimorphism, where one morph is long‐winged and flight capable while the other is short‐winged and flight incapable, is common and believed to be maintained in populations due to trade‐offs to flight capability. In males, macropterous individuals call less than micropterous individuals and as a consequence obtain fewer matings. This trade‐off is hypothesized to be mediated by the energetic costs of calling. In this paper we report results for a path analysis examining lipid weight and DLM (dorso longitudinal muscle) condition of male Gryllus firmus. We found that as DLM condition changes from a nonfunctional to a functional state, call duration decreases, and as lipid weight increases, call duration increases. The most important linked path was wing morph → DLM condition → call duration. This model is consistent with the prediction that the trade‐off between wing morph and call duration is mediated via DLM and lipid stores.     

Immunological larval polyphenism in the map butterfly Araschnia levana reveals the photoperiodic modulation of immunity

The bivoltine European map butterfly (Araschnia levana) displays seasonal polyphenism characterized by the formation of two remarkably distinct dorsal wing phenotypes: The spring generation (A. levana levana) is predominantly orange with black spots and develops from diapause pupae, whereas the summer generation (A. levana prorsa) has black, white, and orange bands and develops from subitaneous pupae. The choice between spring or summer imagoes is regulated by the photoperiod during larval and prepupal development, but polyphenism in the larvae has not been investigated before. Recently, it has been found that the prepupae of A. levana display differences in immunity‐related gene expression, so we tested whether larvae destined to become spring (short‐day) or summer (long‐day) morphs also display differences in innate immunity. We measured larval survival following the injection of a bacterial entomopathogen (Pseudomonas entomophila), the antimicrobial activity in their hemolymph and the induced expression of selected genes encoding antimicrobial peptides (AMPs). Larvae of the short‐day generation died significantly later, exhibited higher antibacterial activity in the hemolymph, and displayed higher induced expression levels of AMPs than those of the long‐day generation. Our study expands the seasonal polyphenism of A. levana beyond the morphologically distinct spring and summer imagoes to include immunological larval polyphenism that reveals the photoperiodic modulation of immunity. This may reflect life‐history traits that manifest as trade‐offs between immunity and fecundity.     

Responses of disparate phenotypically-plastic,melanin-based traits to common cues: limits to the benefits of adaptive plasticity?

The evolution of perfect adaptive phenotypic plasticity of a given trait may be influenced by, among other things, phenotypic costs associated with the expression of a given trait value, relative to alternative trait values. One potential cause of such phenotypic costs is the allocation of limited resources to multiple traits. When multiple traits rely on the same resource, trait values for one adaptively plastic trait might be unavoidably associated with maladaptive trait values for other traits. I address this problem in three traits of Pieris rapae L. (the small cabbage white butterfly) that all rely on the pigment melanin and are adaptively plastic, but have very different functions: wing pattern, immune defense, and pupal color. Cool, short-day rearing conditions simultaneously increased total wing melanization and decreased a melanin-based immune response in females, consistent with predictions. However, cool, short days also reduced the melanin-based immune response in males, despite little effect on male wing melanization. Furthermore, contrary to predictions, these patterns were not altered by differences in dietary resources. Finally, dark-colored rearing backgrounds during pupation substantially increased pupal melanization in both sexes, but was not associated with differences in wing melanization. These results offer only mixed support for the hypothesis of melanin-based trade offs as a source of phenotypic costs to adaptive plasticity in these traits. However, patterns of sexual dimorphism for these traits suggest trade offs might be at work at another level: relative to males, females have consistently more heavily melanized wings but less heavily melanized pupae and immune responses. The reduced immune response under cool, short-day conditions may also have implications for the evolutionary ecology of these butterflies.     

Allometry of a sexual trait in relation to diet experience and alternative mating tactics in two rubyspot damselflies (Calopterygidae: Hetaerina)

Several arguments have been put forward to explain how sexual selection drives the evolution of sexual trait allometry, especially hyperallometry. The ‘positive allometry theory’ suggests that hyperallometry is a rule in all‐secondary sexual traits, whereas the ‘display hypothesis’ suggests that only males in good condition will exhibit hyperallometric sexual display traits. In the present study, we investigated: (1) the condition‐dependence nature (by using two diet treatments that varied in the amount of food provided to the larvae) of a sexually selected trait (wing pigmentation; WP) in recently‐emerged adults of the American rubyspot damselfly, Hetaerina americana, and (2) the scaling relationship between WP and body size (wing and body length) in the rubyspot damselflies H. americana and Hetaerina vulnerata, according to alternative reproductive tactics (ARTs; territorial and nonterritorial males). First, we found support that indicated that diet positively affected WP length, although there was no significant WP allometric pattern in relation to diet regimes. Second, WP was hyperallometric in both Hetaerina species. WP size was similar between ARTs and, in H. americana (but not H. vulnerata), nonterritorial males showed steeper slopes than territorial males when wing length was used. The results obtained support the notion that sexual traits are hyperallometric, although there is no clear pattern in relation to ARTs. © 2013 The Linnean Society of London     

Multiple roles for laccase2 in butterfly wing pigmentation,scale development,and cuticle tanning

Lepidopteran wing scales play important roles in a number of functions including color patterning and thermoregulation. Despite the importance of wing scales, however, we still have a limited understanding of the genetic mechanisms that underlie scale patterning, development, and coloration. Here, we explore the function of the phenoloxidase‐encoding gene laccase2 in wing and scale development in the nymphalid butterfly Vanessa cardui. Somatic deletion mosaics of laccase2 generated by CRISPR/Cas9 genome editing presented several distinct mutant phenotypes. Consistent with the work in other nonlepidopteran insect groups, we observed reductions in melanin pigmentation and defects in cuticle formation. We were also surprised, however, to see distinct effects on scale development including complete loss of wing scales. This study highlights laccase2 as a gene that plays multiple roles in wing and scale development and provides new insight into the evolution of lepidopteran wing coloration.     

Hatching asynchrony and brood reduction influence immune response in Common Kestrel Falco tinnunculus nestlings

The onset of incubation before the end of laying imposes asynchrony at hatching and, therefore, a size hierarchy in the brood. It has been argued that hatching asynchrony might be a strategy to improve reproductive output in terms of quality or quantity of offspring. However, little is known about the mediating effect of hatching asynchrony on offspring quality when brood reduction occurs. Here, we investigate the relationship between phenotypic quality and hatching asynchrony in Common Kestrel Falco tinnunculus nestlings in Spain. Hatching asynchrony did not increase breeding success or nestling quality. Furthermore, hatching asynchrony and brood reduction had different effects on nestlings’ phytohaematogglutinin (PHA)‐mediated immune response and nestling growth. In asynchronous and reduced broods (in which at least one nestling died), nestlings showed a stronger PHA‐mediated immune response and tended to have a smaller body size compared with nestlings raised in synchronous and reduced broods. When brood reduction occurred in broods hatched synchronously, there was no effect on nestling size, but nestlings had a relatively poor PHA‐mediated immune response compared with nestlings raised in asynchronous and reduced broods. We suggest that resources for growth can be directed to immune function only in asynchronously hatched broods, resulting in improved nestling quality, as suggested by their immune response. We also found that males produced a greater PHA‐mediated immune response than females only in brood‐reduced nests without any effect on nestling size or condition, suggesting that females may trade off immune activities and body condition, size or weight. Overall, our results suggest that hatching pattern and brood reduction may mediate resource allocation to different fitness traits. They also highlight that the resolution of immune‐related trade‐offs when brood reduction occurs may differ between male and female nestlings.     

Intrasexual selection favours an immune‐correlated colour ornament in a dragonfly

Sexual signalling is predicted to shape the evolution of sex‐specific ornamentation, and establishing the costs and benefits of ornamentation and the information that ornamentation provides to receivers is necessary to evaluating this adaptive function. Here, we assessed the adaptive function of a common colour ornament in insects, melanin wing ornamentation, using the dragonfly Pachydiplax longipennis. We hypothesized that greater ornamentation would improve territory‐holding success by decreasing aggression that males receive from territorial rivals, but that more ornamented males may have shorter lifespans. Using mark–recapture field observations, we found that more ornamented males had greater territory‐holding success and that viability selection did not act on wing melanization. We then compared the aggression of territorial rivals to decoy males before and after experimentally augmenting wing melanization, finding that males significantly reduced aggression following the manipulation. We next hypothesized that wing melanization would signal fighting ability to territorial rivals by reflecting condition via investment in the costly melanin synthesis pathway. We observed a positive relationship between ornamentation and the likelihood of winning territorial disputes, suggesting that wing melanization provides information about fighting ability to rivals. We also found a positive relationship between melanin‐based immune defence and ornamentation, supporting a link between the signal and condition. We conclude that wing melanization is a condition‐related signal of fighting ability and suggest that this may be a common mechanism promoting the evolution of melanin ornamentation.     

Phenotypic variation in nestlings of a bird of prey under contrasting breeding and diet conditions

Environmental conditions often vary in space and time, and this may explain variation in the expression of phenotypic traits related to individual quality, such as ornamental coloration. Furthermore, the direction and strength of the relationship between coloured trait expression and individual quality might vary under contrasting conditions. These issues have been explored in adult birds but much less so in nestlings, which are more likely to experience different selective pressures and different physiological trade‐offs than adults. Here, we empirically investigated the effects of contrasting breeding and diet conditions on the expression of carotenoid‐based colour traits displayed by marsh harrier (Circus aeruginosus) nestlings. We studied the variation in coloration, body condition, and immune responsiveness of nestlings in four populations over a 5‐year period. We characterized spatiotemporal differences in rearing conditions experienced by C. aeruginosus nestlings in terms of breeding (laying date, clutch size, and number of nestlings hatched and fledged) and diet (percentage of mammal in diet and prey diversity) conditions. We found that breeding conditions influenced the co‐variation between coloration and immune responsiveness in female nestlings, and that diet conditions influenced the condition‐dependence of nestling coloration in later‐hatched nestlings. In addition, breeding conditions influenced nestling body condition and immune responsiveness, whereas diet conditions influenced nestling coloration and body condition. Our study highlights that nestling phenotype (levels of signalling, circulating carotenoids, and immunity) varies both spatially and temporally, and that some of this variation is related to differences in breeding and diet conditions. Moreover, under contrasting conditions, the direction of the relationships between nestling carotenoid‐based coloration and nestling quality may also vary. In order to fully understand the evolution and maintenance of colour traits in nestling birds, studies and experiments should ideally be replicated under contrasting rearing conditions. © 2012 The Linnean Society of London, Biological Journal of the Linnean Society, 2012, ?? , ??–??.     

Experimental test of a trade‐off between moult and immune response in house sparrows Passer domesticus

A trade‐off between immune system and moulting is predicted in birds, given that both functions compete for resources. However, it is unclear whether such a trade‐off exists during post‐breeding moult. This study tests such a trade‐off in the house sparrow (Passer domesticus). Males injected with an antigen (lipopolysaccharide) significantly moulted slower than sham‐injected males. Moreover, males whose seventh primaries were plucked to simulate moult showed smaller immune response to phytohaemagglutinin than control males, in which seventh primaries were clipped. A trade‐off between moult speed and body mass was also found. The results show a clear trade‐off between moult and immune response in the house sparrow: immune response negatively affected moult and moult negatively affected immune response. These findings suggest that only individuals in good condition may have an efficient moult and simultaneously respond effectively in terms of immunity to pathogens, which could explain how plumage traits honestly indicate parasite resistance in birds.     

Positive Relationship between Signalling Time and Flight Capability in the Texas Field Cricket, Gryllus texensis

A trade‐off between dispersal ability and reproduction is generally thought to explain the persistence of wing dimorphism in insects, although this trade‐off has received minimal attention in male insects. Research on male sand cricket, Gryllus firmus, supports the trade‐off hypothesis insofar as flight capable cricket’s spend significantly less time signalling for potential mates than their flightless counterparts. By contrast, here I show that this expected trade‐off between signalling time and wing dimorphism does not exist in a male congener, the Texas field cricket (Gryllus texensis). In G. texensis, flight capable males signal twice as often as flightless males. Thus, unless male G. texensis express trade‐offs between dispersal ability and other, presently unmeasured components of reproduction, the trade‐off hypothesis may not explain the persistence of wing dimorphism in all male insects.     

A test of the relationship between cuticular melanism and immune function in wild‐caught Mormon crickets

Cuticular melanism and innate immune parameters can share common physiological pathways in insects, and this functional connection may contribute to the maintenance of insect colour polymorphisms. However, evidence linking colouration and immune function has been equivocal, particularly when tested in wild populations. The present study investigates phenotypic links between colouration and immune function in migratory Mormon crickets (Anabrus simplex, Haldeman), in which juveniles occur in conspicuous colour variants but mature to become uniformly melanic adults. Wild‐caught insects are used to evaluate the relationship between juvenile colouration and three immune parameters: encapsulation ability, lysozyme‐like activity and phenoloxidase activity. As nymphs, brown crickets are better able to encapsulate an inert implant introduced into the haemocoel than green crickets, although the difference is slight and ceases after they all become darkly‐coloured adults. By contrast, adults that develop from brown nymphs have a higher basal phenoloxidase activity than those that develop from green nymphs, regardless of the fact that all adults are brown. Intrinsic factors other than colouration exert larger effects on immunity: males show stronger encapsulation responses but lower phenoloxidase activity than females, suggesting a sex‐specific trade‐off between these two immune parameters, and adults exhibit higher immune function than nymphs. In summary, modest support is found for a correlation between cuticular melanism and increased immune function in wild Mormon crickets. Additional intrinsic factors such as developmental stage and sex appear to interact with colouration and have a more substantial connection to immune function in the wild.     

Sexual conflicts, loss of flight, and fitness gains in locomotion of polymorphic water striders

In insect wing polymorphism, morphs with fully developed, intermediate, and without wings are recognized. The morphs are interpreted as a trade‐off between flight and flightlessness; the benefits of flight are counterbalanced by the costs of development and the maintenance of wings and flight muscles. Such a trade‐off has been widely shown for reproductive and developmental parameters, and wing reduction is associated with species of stable habitats. However, in this context, the role of water locomotion performance has not been well explored. We chose seven water striders (Heteroptera: Gerridae) as a model to study this trade‐off and its relation to sexual conflicts, namely, Aquarius elongatus (Uhler), Aquarius paludum (Fabr.), Gerris insularis (Motschulsky), Gerris nepalensis Distant, Gerris latiabdominis Miyamoto, Metrocoris histrio (White), and Rhagadotarsus kraepelini Breddin. We estimated the locomotion performance as the legs’ stroke force, measured on tethered specimens placed on water with a force transducer attached to their backs. By dividing force by body weight, we made performance comparisons. We found a positive relationship between weight and force, and a negative one between weight and the force‐to‐weight ratio among species. The trade‐off between water and flight locomotion was manifested as differences in performance in terms of the force/weight ratio. However, the bias toward winged or wing‐reduced morphs was species dependent, and presumably related to habitat preference. Water strider species favouring a permanent habitat (G. nepalensis) showed higher performance in the apterous morph, but in those favouring temporary habitats (A. paludum and R. kraepelini) morphs’ performance did not differ significantly. Males had higher performance than females in all but three species studied (namely, A. elongatus, G. nepalensis, and R. kraepelini); these three have a type II mating strategy with minimized mating struggle. We hypothesized that in type I mating system, in which males must struggle strongly to subdue the female, males should outperform females to copulate successfully. This was not necessarily true among males of species with type II mating.     

Overwintering stages of Callosobruchus chinensis (L.) in the field

Adzuki bean beetle, Callosobruchus chinensis, is a worldwide oligophagous and a field‐to‐storage pest of legumes including adzuki beans (Vigna angularis). Its over‐wintering stage is yet to be confirmed. A series of experiments was carried out at Jinju, in the southern part of the Republic of Korea, to elucidate the overwintering stages. Top‐ and sub‐soil samplings followed by pod and seed samplings from left over plants from adzuki bean fields in the winter of 2015, and an outdoor overwintering test (during Nov 2018 to Jun 2019) by exposing bean seeds harboring different stages (eggs, larvae, pupae, pharates and adults) of laboratory reared C. chinensis to the winter environment were carried out. None of the C. chinensis stages was detected from the top‐ and sub‐soil samples. When the pods and seeds from left over plants were sampled, only a few live pupae were obtained. In the outdoor test with laboratory reared C. chinensis, all the stages (larvae, pupae, and adults), except eggs, were detected on every other weekly samples of infested adzuki bean seeds throughout the winter. These results showed that the overwintering stages of C. chinensis in Jinju, southern Korea, are larvae, pupae, pharates and adults.     

Effects of fluctuating thermal regimes on cold survival and life history traits of the spotted wing Drosophila(Drosophila suzukii)

Drosophila suzukii is an invasive pest causing severe damages to a large panel of cultivated crops.To facili tate its biocontrol with stratcgies such as sterile or incompatible insect techniques,D.suzukid must be mass-produced and then stored and transported under low temperature.Prolonged cold exposure induces chill injuries that can be mitigated if the cold period is interrupted with short warming intervals,referred to as fluctuating thermal regimes(FTR).In this study,we tested how to optimally use FTR to extend the shelf life of D.suzukii under cold storage.Several FTR parameters were asessed:temperature(15,20,25℃),duration(0.5,1,2,3 h),and frequency(every 12,24,36,48 h)of warming intervals,in two wild-type lines and in two developmental stages(pupac and adults).Generally,FTR improved cold storage tolerance with respect to constant low temperatures(CLT).Cold mortality was lower when recovery temperature was 20℃ or higher,when duration was 2 h per day or longer,and when warming interruptions occurred frequently(every 12 or 24 h).Applying an optimized FTR protocol to adults greatly reduced cold mortality over long-term storage(up to 130 d).Consequences of FTR on fitness-related traits were also investigated.For adults,poststorage survival was unaffected by FTR,as was the case for female fecundity and male mating capacity.On the other hand,when cold storage occurred at pupal stage,postorage survival and male mating capacity were altered under CLT,but not under FTR.After storage of pupae,female fecundity was lower under FTR compared to CLT,suggesting an energy trade-off between repair of chill damages and C22 production.This study provides detailed information on the application and optimization of an FTR-based protocol for cold storage of D.suzuki that could be useful for the biocontrol of this pest.     

Life‐history trade‐offs under different larval diets in Drosophila suzukii (Diptera: Drosophilidae)

Most larval drosophilids eat the microorganisms that develop in rotting fruit, a relatively protein‐rich resource. By contrast, the spotted‐wing Drosophila suzukii Matsumara (Diptera: Drosophilidae) uniquely develops in ripening fruit, a protein‐poor, carbohydrate‐rich resource. This shift in larval nutritional niche has led to D. suzukii being a significant agricultural pest in the U.S.A. and Europe. Although occupying a new niche may benefit a species by reducing competition, adaptation in host use may generate trade‐offs affecting fitness. To test the hypothesis that fitness trade‐offs will change with adaptation to novel larval diets, D. suzukii larval development on either a diet of a fresh, ripe blueberry (a natural host) or standard artificial Drosophila media (protein‐rich) is compared and the effect of diet on development time from egg to adult, adult body size and male wing spot area, and female fecundity is assessed. Larval development time differs, with larvae on the blueberry emerging as adults earlier than those on the artificial medium, although other fitness measures do not vary between the two diets. In addition, the faster development time on a blueberry does not trade off with body size as expected, although early fecundity is delayed in females that develop on blueberries. Thus, adaptation to a novel larval diet environment does not come at a cost to the ability to develop in protein‐rich resources.     

Lovesick: immunological costs of mating to male sagebrush crickets

A growing body of evidence suggests that resources invested in reproduction often come at the expense of the ability to mount an immune response. During mating, female sagebrush crickets, Cyphoderris strepitans, consume the ends of the male’s hind wings and ingest his haemolymph. Previous research has shown that this behaviour impairs the ability of males to secure additional matings. One hypothesis to account for this effect is that wing wounding triggers an energetically costly immune response, such that nonvirgin males are unable to sustain the costly acoustical signalling needed to attract additional females. To test this hypothesis, we injected virgin males with lipopolysaccharides (LPS) to provoke an immune response, and monitored their mating success in the field. LPS‐injected virgin males took significantly longer to mate than sham‐injected virgin males, and spent significantly less time calling. We also compared virgin, nonvirgin and experimentally wing‐wounded virgin males with respect to: (1) their ability to encapsulate a foreign invader via the accumulation of haemocytes and deposition of melanin and (2) baseline levels of phenoloxidase (PO), a key enzyme in the biochemical cascade leading to the production of melanin. Although encapsulation ability did not differ with reproductive experience, virgin males had significantly higher levels of PO than either nonvirgin or experimentally wing‐wounded virgin males. These results suggest that wing‐wounding alone is sufficient to impair male immunity, and that males trade‐off investment in reproduction and immunity.     

丝带凤蝶滞育与非滞育蛹及其成虫的形态学观察

丝带凤蝶Sericinus montelus是一种有开发价值的观赏昆虫,以蛹滞育越冬,成虫存在多型现象。本研究从体色、个体大小和蛹腹部刺突长度等方面比较了丝带凤蝶滞育与非滞育蛹及其成虫的形态差异。与非滞育蛹相比,滞育蛹体色较深,触角末端的淡黄色与体色差异明显,3日龄滞育蛹腹部第9节刺突长度是3日龄非滞育蛹的4倍左右,这些差异可以用于该虫蛹滞育早期判别。滞育蛹羽化成虫的翅展和尾突长度显著小于非滞育蛹羽化成虫,且腹部及翅面斑纹也存在明显的差异,这些差异与丝带凤蝶春型、夏型成虫的描述相一致,表明丝带凤蝶成虫季节多型是与滞育相关联的。