Stability of the resistance to lambda-cyhalothrin in the ladybird beetle Eriopis connexa

Natural enemies resistant to insecticides are expected to help control the remaining arthropod pests after insecticide application and, hence, prevent crop damage, pest resurgence, and resistance selection. Field-evolved resistance to lambda-cyhalothrin and to other pyrethroids exhibited by the neotropical ladybird beetle Eriopis connexa (Germar) (Coleoptera: Coccinellidae) has been characterized and enhanced under laboratory selection. In this study, we investigated the stability of the resistance and its relationship with detoxification enzyme activity and biological performance, which are important for a biocontrol agent. One subgroup of the resistant population of E. connexa was established without selection pressure (R-UNSEL) during eight generations, and compared to either a susceptible (SUS) or its parental resistant (R-SEL) population. The resistance ratio in R-UNSEL was reduced by 50% compared to R-SEL between the first and fourth generation without selection pressure, but stayed stable afterwards, from the fifth to the eighth generation. Despite eight generations without selection pressure and reduction in the resistance level, the resistance ratio in R-UNSEL was still 39× greater than in the SUS population. The reduced resistance in R-UNSEL correlated to reduction in esterase activity, but the R-UNSEL maintained greater activity than the SUS group. The absence of selection pressure and reduction in enzyme activity in R-UNSEL did not mitigate the adaptive costs, with 2.7× lower egg production compared to SUS females. These findings indicate that resistance to lambda-cyhalothrin in R-UNSEL has already stabilized in the population. Although the resistance ratio and detoxifying enzymes were reduced in R-UNSEL, the impact on fecundity was maintained. Furthermore, the absence of crossing with wild SUS individuals will allow the R-UNSEL offspring to retain the resistance allowing survival to lambda-cyhalothrin even when used at the highest recommended field rate.     

Biotic interactions between Eriopis connexa and Hippodamia variegata,a native and an exotic coccinellid species associated with alfalfa fields in Chile

Human‐assisted introductions, including those in the context of biological control, are considered to be one of the most important factors of global environmental change. However, the mechanisms underlying environmental changes, such as a decrease in the relative abundance of native species, are poorly understood. Since the introduction of the ladybird beetle, Hippodamia variegata (Goeze) (Coleoptera: Coccinellidae), in Chile in the 1970s for biological control of aphids, a reduction in the relative abundance of the native ladybird beetle Eriopis connexa (Germar) has been noticed. To explore the role of cannibalism, intraguild predation (IGP) or competition as possible mechanisms that might increase dominance of H. variegata over E. connexa, several laboratory experiments were carried out. The native and the exotic species were very similar in their voracity and biotic interactions. Although H. variegata was able to maintain constant reproductive performance, E. connexa reproduction decreased at lower densities of aphids, Acyrthosiphon pisum (Harris) (Hemiptera: Aphididae). The impacts of cannibalism, IGP, and competition exerted by these species were very symmetrical in both larvae and adults. We conclude that these biotic factors may not fully explain the increase in relative abundance of H. variegata. The higher sensitivity of E. connexa to prey patch size, along with other factors such as chemical‐mediated negative interspecific interactions may be operating in alfalfa fields, changing the composition of associated coccinellid assemblages.     

Heterosis and reselection for pyrethroid resistance trait maintenance in the lady beetle Eriopis connexa (Germar)

Exposure of Eriopis connexa (Germar) to pyrethroid residues in agroecosystems has resulted in selection for resistance (R). Pyrethroid resistance allows E. connexa to survive lambda-cyhalothrin applications. Following a field release of E. connexa, development of resistance in an incipient population may depend on three major factors such as the maintenance of: (i) selection pressure, (ii) frequency of mating with susceptible phenotypes (S) and (iii) differential reproductive performance due to the fitness costs associated with resistance. To investigate the potential effects of these three factors on the development of pyrethroid resistance by progeny of field released E. connexa, our experiments included panmictic mating between R and S phenotypes, followed by descendant rearing with and without insecticide selection pressure, reselection and determination of resistance levels. In addition, we measured the reproductive performance of the parental R and S phenotypes and their descendants to assess the cost of resistance after crossing and reselection. Survival of R × S descendants exposed to lambda-cyhalothrin was reduced across successive generations in the absence of selection pressure, but still enhanced after four generations indicating the persistent presence of resistant phenotypes in the population. Under selection pressure with exposure to lambda-cyhalothrin applied at label rates, descendant survival was >50%. Fecundity and survival were higher in the first-generation of crossed R × S females, but higher fecundity was not sustained after reselection. Adults of the R population exhibited a fitness cost, reduced longevity, when compared to S phenotypes and R × S crossed populations. Therefore, resistance maintenance in E. connexa after release will depend on selection pressures imposed by insecticide exposure. In the absence of selection pressure, the phenotype for resistance was reduced, but not completely lost. Further, resistant phenotypes can be reselected following insecticide exposure and this can explain, in part, the high frequency of field-evolved resistance to lambda-cyhalothrin in E. connexa.     

Evolutionary ecology of microsporidia associated with the invasive ladybird Harmonia axyridis

Invasive species are characterized by the rapid growth and spread of their populations after establishing a foothold in new habitats, and there are now many examples of such species negatively affecting biodiversity and the economy. It is unclear why some species can become successful invaders, whereas most (even if closely related) remain noninvasive. We previously proposed a hypothesis that parasites associated with invading species can promote their invasive success if they are harmless toward the invaders but harmful to their competitors and/or predators in the newly colonized habitat. Here we discuss whether microsporidia that have recently been discovered in the invasive ladybird Harmonia axyridis contribute to its invasive success. We show that all H. axyridis beetles sourced from diverse collection sites all over the world carry abundant microsporidia. This suggests that both native and invasive H. axyridis populations are associated with these tolerated parasites, which were likely to have existed in native populations before expansion rather than being acquired in newly colonized areas. We describe the pathogenesis of the microsporidia during different developmental stages of H. axyridis and we address the possibility that the predation of its infected eggs and larvae by competing native ladybird species may lead to their infection and ultimately to their decline. Finally, we discuss our initial hypothesis: microsporidia that are tolerated by an invasive vector insect can be active against susceptible native competitors and/or predator species.     

Life‐history consequences and disease resistance of western tent caterpillars in response to localised,herbivore‐induced changes in alder leaf quality

1. Plants can respond to herbivore damage with phenotypically plastic changes in quality that negatively affect herbivores and prevent subsequent attack – induced defences. 2. The present study tested whether trees respond to herbivory with localised induction, and whether life‐history traits and disease resistance of an insect herbivore are altered on induced branches of the trees. 3. The influences of localised, within‐branch, herbivore‐induced changes in red alder trees (Alnus rubra Bong.) on fitness characteristics of western tent caterpillars (Malacosoma californicum pluviale Dyar) were evaluated. In the field, randomly selected branches of trees were infested with tent caterpillar larvae and the adjacent branches were maintained as non‐infested controls. In the laboratory, larvae were fed leaves from either induced or non‐induced branches through to adult emergence. A second cohort of larvae was challenged with a viral pathogen to compare their disease susceptibility on induced versus non‐induced foliage. 4. Herbivore‐induced, localised responses of damaged branches reduced leaf quality for growth and the fecundity of female western tent caterpillars, but not that of males. Larvae fed induced leaves had a higher survival overall and a reduced mortality due to unidentified non‐viral pathogens than did their counterparts on non‐induced leaves. However, there was no influence of leaf quality on baculovirus‐induced mortality. 5. These findings suggest that localised induced changes in leaf quality could potentially influence populations of tent caterpillars in contradictory ways by reducing their growth rate and fecundity to a modest degree, while improving their survival and resistance to unidentified non‐viral pathogens to a larger extent.     

Effects of early resource limitation and compensatory growth on lifetime fitness in the ladybird beetle (Harmonia axyridis)

Acceleration of growth following a period of diet restriction may result in either complete or partial catch-up in size. The existence of such compensatory growth indicates that organisms commonly grow at rates below their physiological maxima and this implies a cost for accelerated growth. We examined patterns of accelerated growth in response to temporary resource limitation, and assayed both short and long-term costs of this growth in the ladybird beetle Harmonia axyridis. Subsequent to the period of food restriction, accelerated growth resulted in complete compensation for body sizes, although we observed greater larval mortality during the period of compensation. There were no effects on female fecundity or survivorship within 3 months of maturation. Females did not discriminate against males that had undergone compensatory growth, nor did we observe effects on male mating behaviour. However, individuals that underwent compensatory growth died significantly sooner when deprived of food late in adult life, suggesting that longer-term costs of compensatory growth may be quite mild and detectable only under stressful conditions.     

Development and use of a monoclonal antibody to detect semi-digested proteins of the English grain aphid, Sitobion avenae, in the guts of ladybird beetle predators

A monoclonal antibody (McAb), EGA-4A9, was developed to detect the semi-digested proteins of the English grain aphid, Sitobion avenae (Fabricius) (Hemiptera: Aphididae), in predatory ladybird beetles (species of the genera Adonia , Coccinella , Hippodamia , and Propylea ) using the gut homogenate of Adonia variegata (Goeze) (Coleoptera: Coccinellidae) adults which had fed on S. avenae as immunogen. The McAb was selected by screening hybridoma lines for antibodies that bound with the semi-digested aphid proteins in ladybirds. A double antibody sandwich enzyme-linked immuno-sorbent assay (ELISA) using Clonotyping^TM System/HRP showed that it belonged to the IgG2a isotype. It did not cross-react with any of the 21 arthropod species tested besides the ladybird beetles fed on S. avenae with an indirect ELISA. It could still detect the semi-digested proteins in the gut of a ladybird adult, kept at 25 °C, that had ingested one aphid 6 days before. The extended antigen detection period and the high specificity of the antibody indicated that EGA-4A9 could be used to study interactions between English grain aphids and their ladybird predators in the field. Between 28 and 72% of coccinellids collected from the field were positive for English grain aphid protein by ELISA. The percentage of McAb-positive predatory ladybird beetles was positively correlated with the density of S. avenae in wheat fields.     

Gas exchange pattern in the two‐spot ladybird beetle,Adalia bipunctata,differs in dry vs. moist air

Gas exchange patterns in the ladybird beetle, Adalia bipunctata (L.) (Coleoptera: Coccinellidae), were investigated using an infrared gaseous analyser (IRGA) and a coulometric O₂ respirometer (manometric–volumetric system). Before testing, the beetles were kept either in dry (dehydrated) or moist (hydrated) conditions for 1 day. Their subsequent gas exchange patterns did not depend on their state of humidity but rather were controlled by the humidity of the insect chamber during gas exchange measurement. If this chamber contained dry air, the beetles exhibited CO₂ release by burst, which we interpreted as cyclic gas exchange (CGE) with inter‐burst periods, but if the chamber was switched to contain moist air, then cyclic CO₂ release was soon abandoned and a pattern of continuous gas exchange appeared. Measurements with the coulometric respirometer in moist air showed that continuous gas exchange was often associated with weak abdominal pulsations, which we interpreted as active ventilation. Their metabolic rate was lower during gas exchange cycles than during continuous gas exchange. We revealed that in the ladybird beetle metabolic rate increased in moist air when the gas exchange pattern transitioned from cyclic to continuous.     

Predators modify the temperature dependence of life‐history trade‐offs

Although life histories are shaped by temperature and predation, their joint influence on the interdependence of life‐history traits is poorly understood. Shifts in one life‐history trait often necessitate shifts in another—structured in some cases by trade‐offs—leading to differing life‐history strategies among environments. The offspring size–number trade‐off connects three traits whereby a constant reproductive allocation (R) constrains how the number (O) and size (S) of offspring change. Increasing temperature and size‐independent predation decrease size at and time to reproduction which can lower R through reduced time for resource accrual or size‐constrained fecundity. We investigated how O, S, and R in a clonal population of Daphnia magna change across their first three clutches with temperature and size‐independent predation risk. Early in ontogeny, increased temperature moved O and S along a trade‐off curve (constant R) toward fewer larger offspring. Later in ontogeny, increased temperature reduced R in the no‐predator treatment through disproportionate decreases in O relative to S. In the predation treatment, R likewise decreased at warmer temperatures but to a lesser degree and more readily traded off S for O whereby the third clutch showed a constant allocation strategy of O versus S with decreasing R. Ontogenetic shifts in S and O rotated in a counterclockwise fashion as temperature increased and more drastically under risk of predation. These results show that predation risk can alter the temperature dependence of traits and their interactions through trade‐offs.     

Life‐history traits of the Whiting polyploid line of the parasitoid Nasonia vitripennis

In hymenopterans, males are normally haploid (1n) and females diploid (2n), but individuals with divergent ploidy levels are frequently found. In species with ‘complementary sex determination’ (CSD), increasing numbers of diploid males that are often infertile or unviable arise from inbreeding, presenting a major impediment to biocontrol breeding. Non‐CSD species, which are common in some parasitoid wasp taxa, do not produce polyploids through inbreeding. Nevertheless, polyploidy also occurs in non‐CSD Hymenoptera. As a first survey on the impacts of inbreeding and polyploidy of non‐CSD species, we investigate life‐history traits of a long‐term laboratory line of the parasitoid Nasonia vitripennis (Walker) (Hymenoptera: Pteromalidae) (‘Whiting polyploid line’) in which polyploids of both sexes (diploid males, triploid females) are viable and fertile. Diploid males produce diploid sperm and virgin triploid females produce haploid and diploid eggs. We found that diploid males did not differ from haploid males with respect to body size, progeny size, mate competition, or lifespan. When diploid males were mated to many females (without accounting for mating order), the females produced a relatively high proportion of male offspring, possibly indicating that these males produce less sperm and/or have reduced sperm functionality. In triploid females, parasitization rate and fecundity were reduced and body size was slightly increased, but there was no effect on lifespan. After one generation of outbreeding, lifespan as well as parasitization rate were increased, and a body size difference was no longer apparent. This suggests that outbreeding has an effect on traits observed in an inbred polyploidy background. Overall, these results indicate some phenotypic detriments of non‐CSD polyploids that must be taken into account in breeding.     

Tracing dietary origins of aphids and the predatory beetle Propylea japonica in agricultural systems using stable isotope analyses

Tracing dietary origins of the predatory beetle Propylea japonica (Thunberg) (Coleoptera: Coccinellidae) aids understanding their roles in the food web and provides information to develop strategies for effective conservation in agroecosystems comprised of wheat [Triticum aestivum L. (Poaceae)], cotton [Hirsutum spp. (Malvaceae)], and maize [Zea mays L. (Poaceae)]. Intrinsic markers of carbon and nitrogen stable isotope ratios (δ¹³C and δ¹⁵N) in P. japonica need to be developed to ascertain the source(s) of diet. Experiments were carried out to examine the changes of δ¹³C and δ¹⁵N among the three crops, pests (wheat, cotton, and maize aphids; all Hemiptera: Aphididae), and P. japonica fed on aphids of each of the three crops. Results indicated that δ¹³C values in P. japonica fed on wheat, cotton, and maize aphids were ?27.2 to ?26.5‰, ?24.2 to ?23.9‰, and ?11.0 to ?10.7‰, respectively, whereas their δ¹⁵N values were 1.1 to 2.9‰, 6.0 to 7.4‰, and ?0.6 to 0.1‰, respectively. δ¹³C and δ¹⁵N plots clearly identify the three crops, the dietary origins of the aphids, and the host origins of the aphid prey consumed by the ladybird beetles, as each pathway displays a non‐overlapping pattern. Based on the values of δ¹³C and δ¹⁵N of the three food webs, dietary origins can be traced in the predatory beetle P. japonica derived from wheat, cotton, and maize crops.     

Effect of resource gradient on age and size at maturity and their influence on early‐life fecundity in the predatory Asian lady beetle,Harmonia axyridis

Variation in food availability impacts the performance of insects in terms of their size and age to maturity and fecundity. Age at maturity determines how quickly individuals in a population can start to reproduce and how much they can reproduce. Results from studies on various insect species show that food availability influences the size and fecundity of adult females. It is predicted that under poor growth conditions, variation in size is low, but variation in age at maturity is considerable. This prediction was examined in a widely distributed lady beetle species, Harmonia axyridis (Pallas) (Coleoptera: Coccinellidae), a predator of aphids and coccids. Using a food gradient from low to high aphid prey density, performance of females that were reared on excess food was recorded for pre‐reproductive duration, size at reproductive maturity, number of aphids consumed, and fecundity in the first 10 days of their reproductive period. Results suggested that female H. axyridis that were reared on surplus food when kept at low prey density (poor growth condition) took, on average, three times longer to attain maturity and produced, on average, 14 times fewer eggs than females that were also reared on surplus food, but kept at high prey density (good growth condition). Females performed best at a prey density of 30 aphids per female per 150 cm². Results suggested that the current food availability significantly influenced the age and size of females at maturity and their fecundity. Age and size at maturity of female lady beetles showed non‐linear responses to prey density as well as the occurrence of a minimum size of females, below which H. axyridis females fail to mature. The steep slope recorded at lower prey densities suggests relatively high variation in age at maturity but low variation in size.     

Fitness costs associated with acetyl‐coenzyme A carboxylase mutations endowing herbicide resistance in American sloughgrass (Beckmannia syzigachne Steud.)

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Dietary complementation across life stages in the polyphagous lady beetle Coleomegilla maculata

We investigated the life history consequences of changes in diet between larval and adult life stages in the polyphagous lady beetle Coleomegilla maculata DeGeer (Coleoptera: Coccinellidae). Beetles were reared on three larval diets: greenbug, Schizaphis graminum Rondani (Homoptera: Aphididae), eggs of the flour moth, Ephestia kuehniella Zeller (Lepidoptera: Pyralidae), and bee pollen. The reproductive performance of females was then evaluated on an adult diet of either greenbug or moth eggs. Moth eggs appeared to be the most suitable diet for larvae, yielding the largest adults, and pollen the least suitable, resulting in the smallest adults and greatly extended developmental time. Pollen‐reared beetles tended to have lower fecundity and fertility than those reared on animal protein, regardless of adult diet. Female fitness was generally increased by a change in diet upon emergence to the alternative source of animal protein, suggesting that dietary complementation occurred across life stages. Among females reared on greenbug, a change of diet to moth eggs reduced the period required for production of 12 clutches and increased egg fertility compared to continued feeding on greenbug. Among females reared on moth eggs, a change of diet to greenbug increased fecundity compared to continued feeding on moth eggs. Among females fed an adult diet of greenbug, those fed moth eggs as larvae had faster production of 12 clutches and higher fecundity. We discuss these novel results in the context of coccinellid life history and ecology and their potential implications for other insects that are predatory as both larvae and adults.     

Cryptic local adaptation of the herbivorous ladybird beetle Henosepilachna pustulosa in the ability to use the thistle Cirsium boreale

Local adaptation to different host plants is important in the diversification of phytophagous insects. Thus far, much evidence of the local adaptation of insects with respect to host use at the physiological level has been gathered from systems involving less mobile insects and/or divergent hosts such as plants belonging to different families or genera. On the other hand, the prevalence of such local adaptation of insects with moderate or high dispersal ability to the intraspecific variation of herbaceous hosts is largely unknown. In the present study, we examined the occurrence and degree of local adaptation of the herbivorous ladybird beetle Henosepilachna pustulosa (Kôno) (Coleoptera: Coccinellidae) to its primary host, the thistle Cirsium boreale Kitam. (Asteraceae), through reciprocal laboratory experiments using beetles and thistles from three locations with a range of approximately 200 km. Concerning the larval developmental ability, obvious patterns of local adaptation to the thistles from respective natal locations were detected, at least in some combinations of beetle populations. Similar tendencies were detected concerning adult feeding acceptance, although the statistical support was somewhat obscure. Overall, our results indicate that the degree of local adaptation of insect species with moderate dispersal ability to conspecific herbaceous hosts is occasionally as strong as that involving less mobile insects and/or heterospecific hosts, indicating the potential of such cryptic local adaptation to promote ecological/genetic differentiation of phytophagous insect populations.     

Life‐history strategy varies with the strength of competition in a food‐limited ungulate population

Fluctuating population density in stochastic environments can contribute to maintain life‐history variation within populations via density‐dependent selection. We used individual‐based data from a population of Soay sheep to examine variation in life‐history strategies at high and low population density. We incorporated life‐history trade‐offs among survival, reproduction and body mass growth into structured population models and found support for the prediction that different life‐history strategies are optimal at low and high population densities. Shorter generation times and lower asymptotic body mass were selected for in high‐density environments even though heavier individuals had higher probabilities to survive and reproduce. In contrast, greater asymptotic body mass and longer generation times were optimal at low population density. If populations fluctuate between high density when resources are scarce, and low densities when they are abundant, the variation in density will generate fluctuating selection for different life‐history strategies, that could act to maintain life‐history variation.     

Life‐history traits predict perennial species response to fire in a desert ecosystem

The Mojave Desert of North America has become fire‐prone in recent decades due to invasive annual grasses that fuel wildfires following years of high rainfall. Perennial species are poorly adapted to fire in this system, and post‐fire shifts in species composition have been substantial but variable across community types. To generalize across a range of conditions, we investigated whether simple life‐history traits could predict how species responded to fire. Further, we classified species into plant functional types (PFTs) based on combinations of life‐history traits and evaluated whether these groups exhibited a consistent fire‐response. Six life‐history traits varied significantly between burned and unburned areas in short (up to 4 years) or long‐term (up to 52 years) post‐fire datasets, including growth form, lifespan, seed size, seed dispersal, height, and leaf longevity. Forbs and grasses consistently increased in abundance after fire, while cacti were reduced and woody species exhibited a variable response. Woody species were classified into three PFTs based on combinations of life‐history traits. Species in Group 1 increased in abundance after fire and were characterized by short lifespans, small, wind‐dispersed seeds, low height, and deciduous leaves. Species in Group 2 were reduced by fire and distinguished from Group 1 by longer lifespans and evergreen leaves. Group 3 species, which also decreased after fire, were characterized by long lifespans, large non‐wind dispersed seeds, and taller heights. Our results show that PFTs based on life‐history traits can reliably predict the responses of most species to fire in the Mojave Desert. Dominant, long‐lived species of this region possess a combination of traits limiting their ability to recover, presenting a clear example of how a novel disturbance regime may shift selective environmental pressures to favor alternative life‐history strategies.