Aphid Diet Research Articles

THE USE OF THREE APHID SPECIES FOR THE PREDATORY BUG PODISUS BREEDING

Podisus maculiventris, the spined soldier bug, is one of the most promising entomophages for agricultural plants protection. Most often the larvae of Galleria mellonella are used for Podisus maculiventris rearing, but this method is rather expensive and sometimes not reliable. The comparative tests of 3 aphid species (Schizaphis graminum, Megoura viciae and Myzus persicae) as food for predatory bug nymphs have been conducted. The study used the following criteria: nymphs survival and developmental time; emerging bugs weight; preoviposition period duration; adult bugs fecundity and longevity; egg batches volume and number; egg viability. It is shown that the development and reproductive potential of predatory bug are decreasing in the majority of cases. However, an option to use aphids for spined soldier bug rearing has been found, namely feeding the nymphs until the 3rd instar, inclusively. The survival rate of nymphs was reduced by 20.6 % and the nymph development time was increased by 20–25 % but can be improved by predatory bug adaptation to the aphid diet during artificial selection. The other indicators of development and reproductive potential important for mass rearing of predator did not change significantly. A slight decrease in the viability of eggs is not practically important since the nymphs and adults feeding are most costly. in spined soldier bug mass rearing. Undoubtedly, a positive effect of predator nymphs feeding with aphids is the decrease of preoviposition period.

Dealing with food shortage: larval dispersal behaviour and survival on non‐prey food of the hoverfly Episyrphus balteatus

1. Predatory larvae often have to face food shortages during their development, and thus the ability to disperse and find new feeding sites is crucial for survival. However, the dispersal capacity of predatory larvae, the host finding cues employed, and their use of alternative food sources are largely unknown. These aspects of the foraging behaviour of the aphidophagous hoverfly (Episyrphus balteatus De Geer) larvae were investigated in the present study.2. It was shown that these hoverfly larvae do not leave a plant as long as there are aphids available, but that dispersing larvae are able to find other aphid colonies in the field. Dispersing hoverfly larvae accumulated on large aphid colonies, but did not distinguish between different pea aphid race–plant species combinations. Large aphid colonies might be easier to detect because of intensified searching by hoverfly larvae following the encounter of aphid cues like honeydew that accumulate around large colonies.3. It was further shown that non‐prey food, such as diluted honey or pollen, was insufficient for hoverfly larvae to gain weight, but prolonged the survival of the larvae compared with unfed individuals. As soon as larvae were switched back to an aphid diet, they rapidly gained weight and some pupated after a few days. Although pupation and adult hatching rates were strongly reduced compared with hoverflies continuously fed with aphids, the consumption of non‐prey food most probably increases the probability that hoverfly larvae find an aphid colony and complete their development.

Effect of nutritious and toxic prey on food preference of a predaceous ladybird, Coccinella septempunctata (Coleoptera: Coccinellidae)

We investigated the predatory potential and food preference of different life stages of Coccinella septempunctata L. for a nutritious aphid (mustard aphid, Lipaphis erysimi) and toxic aphid (cabbage aphid, Brevicoryne brassicae). We provided all the life stages of C. septempunctata with either L. erysimi or B. brassicae and found that the second, third and fourth instar larvae and adult females of this predator consumed daily greater numbers of L. erysimi. However, the first instar larvae and adult males consumed similar numbers of both of these aphids. In choice condition, each larva, adult males and females were each provided separately with a mixed aphid diet in three proportions (i.e. low: high, equal: equal and high: low densities of L. erysimi: B. brassicae). We hypothesized that life stages of C. septempunctata will prefer L. erysimi regardless of its proportions. Laboratory experiments supported this hypothesis only at the adult level in terms of high values of β and C preference indices. However, it rejects this hypothesis at the larval level, as larvae preferred B. brassicae when provided with certain combinations and showed no preference in a few combinations. We infer that mixtures of nutritious and toxic aphids may enable this ladybird to overcome any probable nutritional deficiency and/or reduce the toxicity of a toxic diet, especially for the larvae. Results of the treatment in which a high proportion of B. brassicae were consumed along with fewer L. erysimi indicates that a mixed diet could be better for the development of immature stages of C. septempunctata.

Cucurbit extrafascicular phloem has strong negative impacts on aphids and is not a preferred feeding site

Cucurbits have long been known to possess two types of phloem: fascicular (FP) within vascular bundles and extrafascicular phloem (EFP) surrounding vascular bundles and scattered through the cortex. Recently, their divergent composition was revealed, with FP having high sugar content consistent with conventional phloem, but EFP having much lower sugar levels and a very different proteome. However, the evolutionary advantages of possessing both FP and EFP have remained unclear. Here, we present four lines of quantitative evidence that together support the hypothesis that FP represents a typical phloem and is an attractive diet for aphids, whereas aphids avoid feeding on EFP. First, aphid stylet track endings were more abundant near the abaxial FP element of minor veins, suggesting a feeding preference for FP over EFP. Second, sugar profiles from stylet exudates were wholly consistent with FP origins, further supporting preference for FP and avoidance of EFP. Third, supplementation of EFP exudate into artificial diets confirmed an aversion to EFP in choice experiments. Finally, EFP exudate had negative effects on aphid performance. On the basis of aphids' inability to thrive on EFP, we conclude that EFP is atypical and perhaps should not be classed as a phloem system.

Growth and development of ladybird beetle Coccinella septempunctata L. (Coleoptera: Coccinellidae), on plant and animal based protein diets

Different protein sources from plant and animal origin viz., soybean flour (SF-AD) and soaked soybean (SS-AD), bee pollen (BP-AD), honey bee drone larvae (DL-AD) and frozen aphids (AF-AD) were assessed as an artificial diet of C. septempunctata in comparison to their natural diet live aphids. Highest growth index was obtained with SS-AD (4.05) diet almost similar to control (4.0), followed by SF-AD, BP-AD, DL-AD and AF-AD as 3.8, 2.4, 1.98 and 1.94 respectively. Similarly, data showed that success index of the adults fed on an artificial diet containing soybean (SS-AD=1.03, SF-AD=0.98) was almost similar to control (1.0), whereas the diets containing bee pollen, drone larvae, and frozen aphids was lower than control as 0.83, 0.84 and 0.78, respectively. Protein concentration was highest in live aphid (5.9μg/ml) diet followed by SS-AD (5.6), SF-AD (5.2), BP-AD (3.4), AF-AD (2.2) and DL AD (1.3). The results indicated that soybean based diets were more or equivalently suitable to beetles for their growth and development likewise their natural prey and the efficiency of artificial diets was related to its protein concentration.

Artificial tritrophic exposure system for environmental risk analysis on aphidophagous predators.

We evaluated an artificial tritrophic exposure system for use in ecotoxicological evaluations of environmental stressors on aphidophagous predators. It consists of an acrylic tube with a Parafilm M sachet containing liquid aphid diet, into which can be added environmental stressors. Immature Cycloneda sanguinea, Harmonia axyridis and Chrysoperla externa, and adult H. axyridis were reared on Myzus persicae. Larval and pupal development and survival of all species and reproductive parameters of H. axyridis were similar to published results. The system provides a suitable tritrophic exposure route, enables ex-ante evaluation of stressors, and improves the accuracy of the assessment.

Herbivore Diet Breadth and Host Plant Defense Mediate the Tri-Trophic Effects of Plant Toxins on Multiple Coccinellid Predators.

Host plant defenses are known to cascade up food chains to influence herbivores and their natural enemies, but how herbivore and predator traits and identity mediate such tri-trophic dynamics is largely unknown. We assessed the influence of plant defense on aphid and coccinellid performance in laboratory trials with low- vs. high-glucosinolate varieties of Brassica napus, a dietary specialist (Brevicoryne brassicae) and generalist (Myzus persicae) aphid, and five species of aphidophagous coccinellids. The performance of the specialist and generalist aphids was similar and unaffected by variation in plant defense. Aphid glucosinolate concentration and resistance to predators differed by aphid species and host plant defense, and these effects acted independently. With respect to aphid species, the dietary generalist aphid (vs. specialist) had 14% lower glucosinolate concentration and coccinellid predators ate three-fold more aphids. With respect to host plant variety, the high-glucosinolate plants (vs. low) increased aphid glucosinolate concentration by 21%, but had relatively weak effects on predation by coccinellids and these effects varied among coccinellid species. In turn, coccinellid performance was influenced by the interactive effects of plant defense and aphid species, as the cascading, indirect effect of plant defense was greater when feeding upon the specialist than generalist aphid. When feeding upon specialist aphids, low- (vs. high-) glucosinolate plants increased coccinellid mass gain by 78% and accelerated development by 14%. In contrast, when feeding upon generalist aphids, low- (vs. high-) glucosinolate plants increased coccinellid mass gain by only 11% and had no detectable effect on development time. These interactive effects of plant defense and aphid diet breadth on predator performance also varied among coccinellid species; the indirect negative effects of plant defenses on predator performance was consistent among the five predators when transmitted via the dietary specialist aphid, but these effects varied substantially among predators—in both the magnitude and direction—when transmitted via the dietary generalist aphid. Accordingly, the cascading effect of plant defense on predators was stronger in magnitude and more consistent among predator taxa when transmitted by the specialist than generalist herbivore. Overall, these findings support a central role of herbivore diet breadth in mediating both the strength and contingency of tri-trophic interactions.

Host nutritional status mediates degree of parasitoid virulence

Parasitic organisms rely on the resources of their hosts to obtain nutrients essential for growth and reproduction. Insect parasitoids constitute an extreme condition since they develop in a single host from which they typically consume all available resources. As a result, the host is killed following parasitism. However, a few intriguing cases of host survival have been reported wherein hosts resume foraging and may even reproduce following parasitoid emergence. Yet, the ultimate and proximate mechanisms responsible for host recovery remain unresolved. We tested the impact of host nutrition on host fate and parasitoid fitness, using the association between Dinocampus coccinellae and the spotted lady beetle Coleomegilla maculata. Under laboratory conditions, we fed parasitized ladybirds on different aphid diets, with or without pollen. In the field, we followed the fate of parasitized ladybirds during seasonal variations in pollen and aphid abundance. We found that ladybirds fed on aphids or a combination of aphids and pollen recovered more frequently from parasitism (from 65 to 81%) than those eating only pollen (48%). Field data suggest that the fate of parasitized ladybirds is also related to food availability. On the other hand, when hosts fed on a combination of aphids and pollen, consequences for parasitoid fitness were often ‘all‐or‐nothing’: parasitoid emergence rate was the lowest of all host nutrition regimes (∼50%), but parasitoids that did emerge were larger than individuals emerging from other host nutrition regimes. Laboratory and field results concur to show that host nutritional status during parasitoid development significantly influences both host fate and parasitoid fitness.

Development and Reproduction of Chrysoperla externa (Hagen) (Neuroptera: Chrysopidae) Fed on Myzus persicae (Sulzer) (Hemiptera: Aphididae) Vectoring Potato leafroll virus (PLRV).

The aim of this study was to evaluate the biological parameters of Chrysoperla externa (Hagen) while feeding on Myzus persicae (Sulzer) acting as a vector of potato leafroll virus (PLRV). In laboratory experiments, three different diets were offered ad libitum to C. externa during the larval period: M. persicae fed on PLRV-infected potato leaves, M. persicae fed on uninfected potato leaves, and eggs of the factitious prey Anagasta kuehniella (Zeller) as the control. The following parameters were studied: the developmental time and survival rate of the larval and pupal stages, the sex ratio, the proportion of fertile females, female fecundity and egg viability, and the survival curve of the first 30 days after adult emergence. PLRV-infected aphids influenced the C. externa larval developmental time and survival compared to PLRV-uninfected aphids and A. kuehniella eggs. The pupal developmental time of C. externa was shorter when fed on aphids compared to A. kuehniella eggs, but no differences were recorded between the PLRV-infected and uninfected aphid diets. Additionally, no differences were observed for pupal survival and reproduction. However, adult survival was affected by the prey type, as 75% of C. externa control adults remained alive at an age of 30 days compared to 51 and 54% for those fed on PLRV-uninfected and infected aphids, respectively.

Disrupting Buchnera aphidicola, the endosymbiotic bacteria of Myzus persicae, delays host plant acceptance

Myzus persicae Sulzer, like almost all aphids, associates with the endosymbiotic bacterium, Buchnera aphidicola. Although the accepted function of B. aphidicola is to complete the aphid diet with nutrients such as essential amino acids and vitamins, there is evidence that the bacteria may participate in the plant–insect interaction. Moreover, bacterial proteins with potential effector action on the metabolism of the host plant have been identified in the saliva of M. persicae. However, the possible involvement of B. aphidicola in relation to host plant acceptance by aphids needs further investigation. The aim of this study was to evaluate the effect that the disruption of the B. aphidicola–M. persicae symbiosis has on aphid feeding behaviour and on the expression of aphid salivary genes. The antibiotic rifampicin was administrated to adult aphids through artificial diets to disrupt the bacterial primary endosymbionts. Comparisons were made with control aphids, feeding from diet without rifampicin, as well as normal aphids fed on radish plants. Differences were found in the feeding behaviour of aposymbiotic aphids, which had delayed host acceptance and problems during stylet penetration into host plants. It was also found that B. aphidicola disruption down-regulated the expression of the Mp63 salivary protein gene. Together, these results indicate that B. aphidicola plays a role in plant–aphid interactions. The validity of the use of artificial diets in plant–aphid studies is also discussed.

Indigenous Aphid Predators Show High Levels of Preadaptation to a Novel Prey, Melanaphis sacchari (Hemiptera: Aphididae).

The performance of four aphid predators, Hippodamia convergens Guerin-Meneville, Coleomegilla maculata DeGeer, Chrysoperla carnea Stephens and Orius insidiosus Say was compared on three prey species: Schizaphis graminum Rondani, Melanaphis sacchari (Zehntner), and Ephestia kuehniella Zeller eggs. Species predatory in both life stages (all except Ch. carnea) were reared on E. kuehniella eggs and switched to aphid prey for assessment of reproduction. Differences were greater between the E. kuehniella and aphid diets than between the two aphid species. Juvenile survival was high for all predators on all prey, except for O. insidiosus, which had survival on E. kuehniella > S. graminum > M. sacchari. The fastest development of Ch. carnea and O. insidiosus was obtained on E. kuehniella, whereas H. convergens developed fastest on S. graminum, and C. maculata did not differ among diets. S. graminum also yielded the largest H. convergens adults, whereas the largest adults of other predators were obtained on E. kuehniella. Female fecundity and egg viability were similarly high on both aphid diets for H. convergens and C. maculata, whereas, on E. kuehniella, 50% of the former entered reproductive diapause and the latter species had reduced fecundity. Reproductive success of Ch. carnea was S. graminum = M. sacchari > E. kuehniella, but it was similar among treatments for O. insidiosus, although female infertility ranged from 25 to 37.5%. We concluded that all the predators studied are preadapted to utilize sugarcane aphid as prey and have excellent potential to provide sustainable biological control of this newly invasive pest.

Infection of host plants by Cucumber mosaic virus increases the susceptibility of Myzus persicae aphids to the parasitoid Aphidius colemani.

Plant viruses can profoundly alter the phenotypes of their host plants, with potentially far-reaching implications for ecology. Yet few studies have explored the indirect, host-mediated, effects of plant viruses on non-vector insects. We examined how infection of Cucurbita pepo plants by Cucumber mosaic virus (CMV) impacted the susceptibility of aphids (Myzus persicae) to attack by the parasitoid wasp Aphidius colemani. In semi-natural foraging assays, we observed higher rates of aphid parasitism on infected plants compared to healthy plants. Subsequent experiments revealed that this difference is not explained by different attack rates on plants differing in infection status, but rather by the fact that parasitoid larvae successfully complete their development more often when aphid hosts feed on infected plants. This suggests that the reduced nutritional quality of infected plants as host for aphids—documented in previous studies—compromises their ability to mount effective defenses against parasitism. Furthermore, our current findings indicate that the aphid diet during parasitoid development (rather than prior to wasp oviposition) is a key factor influencing resistance. These findings complement our previous work showing that CMV-induced changes in host plant chemistry alter patterns of aphid recruitment and dispersal in ways conducive to virus transmission.

Feeding History Affects Intraguild Interactions between Harmonia axyridis (Coleoptera: Coccinellidae) and Episyrphus balteatus (Diptera: Syrphidae).

While the effect of several factors such as predator and prey size, morphology and developmental stage on intraguild predation (IGP) is widely investigated, little is known about the influence of diet on the occurrence and outcome of IGP. In the present study, the effect of the diet experienced during larval development on IGP between the ladybird Harmonia axyridis and the syrphid Episyrphus balteatus is investigated. Four diets were tested for H. axyridis: eggs of the Mediterranean flour moth Ephestia kuehniella, pea aphids, Acyrthosiphon pisum, in an ad libitum amount, pea aphids in a limited amount, and honey bee pollen. For E. balteatus only the two aphid diets were tested. First, experiments were performed to determine the quality of the various diets for development of both predators. Second, IGP experiments between H. axyridis and E. balteatus were performed both in Petri dishes and on potted pepper plants. The diet of both species influenced the incidence of IGP between H. axyridis and E. balteatus both in Petri dishes and on potted plants. In general, smaller larvae of H. axyridis (those fed on poor or restricted diet) fed more on hoverflies than large (well-nourished) ladybird larvae. Further, poorly nourished (smaller) larvae of E. balteatus were more susceptible to predation than well-fed (larger) hoverfly larvae. The observed effects were not only due to the lower fitness of larvae of both predators reared on an inferior quality diet but also to changes in predator behaviour. The results from this study show that IGP interactions are influenced by a multitude of factors, including feeding history of the organisms involved, and emphasize the importance of taking these factors into account in order to fully understand the ecological relevance of IGP.

Egg cannibalism by ladybird larvae is less frequent than expected from the nutritional benefit accrued to cannibals

AbstractEgg cannibalism is a widespread phenomenon in predatory arthropods. However, conflicting results have been reported regarding the nutritional value of conspecific eggs. Therefore, evaluation of the value of a mixed diet of conspecific eggs and aphids for survival and growth of Adalia bipunctata (Coccinellidae) larvae was tested. Subsequently, the propensity for cannibalism of naive and experienced larvae was assessed in two experiments in which the relative density and quality of conspecific eggs were manipulated in an experimental arena. It was found that larvae that were fed a mixed diet of conspecific eggs and aphids moulted into larger adults than those fed either aphids or eggs, and those that fed on conspecific eggs lost less mass than those fed only aphids during pupal stage. Additionally, in an experimental arena, attacks on aphids were more frequent than expected when conspecific eggs occupied 50% and 75% of the patches. When 50% of patches were occupied by conspecific eggs, the preference for aphids was less marked when larvae had previously experienced cannibalism (76% vs. 52% respectively) or when offered in the arena conspecific egg the cuticular hydrocarbons of which had been removed (76% vs. 48%, respectively). However, cannibalism was not enhanced if larvae experienced heterospecific prey shortages, but were supplemented with an artificial diet. Given that prey choice in A. bipunctata larvae is driven by chemical cues and that hydrocarbons on the egg surfaces and in larval tracks are very similar, we hypothesize that the naive larvae avoid eggs because of the uncertainty that those hydrocarbons indicate either eggs or conspecific larvae.

Development and survivorship of a predatory lady beetle, Coccinella novemnotata, on various aphid diets

Ex situ rearing of Coccinella novemnotata Herbst (Coleoptera: Coccinellidae), a Nearctic native that has declined precipitously, may be important for experimentation and conservation. Rearing success may depend on optimizing an aphid prey diet. The objective was to compare development, survivorship and adult size of C. novemnotata reared on diets of various aphid (Hemiptera: Aphididae) species. Diets of Acyrthosiphon pisum (Harris) and A. pisum + Rhopalosiphum padi L. were most suitable for rearing C. novemnotata. Single species diets of other aphids had low suitability for C. novemnotata. Combining A. pisum with one of the other aphid species improved diet suitability compared to diets of other species alone. Knowledge of C. novemnotata development and survival on various aphid species may not only aid in ex situ rearing, but could also be used to identify habitats where C. novemnotata may be extant or those with suitable prey for reestablishment or augmentation of C. novemnotata.

Do defensive chemicals facilitate intraguild predation and influence invasion success in ladybird beetles?

Egg predation and cannibalism are believed to be common phenomena among many species of aphidophagous predatory ladybird beetles despite the presence of alkaloid based defensive chemicals in all life stages. We identified defensive chemicals from eggs of three congeneric species, one introduced into North America (Coccinella septempunctata L.), and two native (C. transversoguttata richardsoni Brown, and C. novemnotata Herbst), and examined the effects of ingested defensive chemicals on first instars. Ingested congeneric alkaloids were not toxic to first instars, likely because the three congeners produce the same principal alkaloids, precoccinelline and coccinelline, in similar amounts. First instars of the three congeners accumulated alkaloids ingested through egg cannibalism and congeneric predation. Egg consumption doubled the amount of alkaloids in first instars when they fed on conspecific or congeneric eggs, in comparison to a pea aphid diet. No detrimental effects of ingested congeneric alkaloids on development or survival of first instars were observed among these congeners. Chemical defenses of eggs are therefore not likely to be important in favoring the invasive species, C. septempunctata, in interactions with these native congeneric species. Because the invasive species is the most aggressive predator, having the same types of alkaloids may facilitate disproportionate intraguild predation on native congeners by C. septempunctata thereby potentially enhancing the invasion success of this introduced species.

Relative suitability of the common pistachio psyllid, Agonoscena pistaciae (Hemiptera: Aphalaridae), as prey for the two-spotted ladybird, Adalia bipunctata (Coleoptera: Coccinellidae)

The suitability of Agonoscena pistaciae Burckhardt & Lauterer as a prey for Adalia bipunctata (Linnaeus) was evaluated by studying the predator’s development and reproduction on this species in comparison to reference diets of nymphs of Myzus persicae (Sulzer) and eggs of Ephestia kuehniella Zeller. Both larval and adult A. bipunctata fed voraciously on A. pistaciae. The development time of the ladybird was shorter when fed on M. persicae and A. pistaciae and longer on E. kuehniella. The survival rate was 87% on M. persicae and 85% on A. pistaciae, both significantly greater than on E. kuehniella eggs (63%). The ladybirds were heaviest at eclosion and their fecundity was higher on M. persicae than on A. pistaciae or E. kuehniella. Both the aphid and psyllid diets yielded higher R0, rm values and lower T and DT values than E. kuehniella eggs. Based on total development time, immature survival and adult fecundity, the relative suitability for A. bipunctata was M. persicae>A. pistaciae>E. kuehniella. When ladybirds were reared on psyllids, they showed no preference between aphid or psyllid diets, but when raised on M. persicae, they preferred an aphid diet. A field experiment showed that A. bipunctata preferred to oviposit on pistachio trees at a height of 150–200cm, i.e. towards the top. The results indicate that A. pistaciae constitutes a complete food for A. bipunctata, supporting both completed development and successful reproduction.

Development times and age-specific life table parameters of the native lady beetle species Coccinella novemnotata (Coleoptera: Coccinellidae) and its invasive congener Coccinella septempunctata (Coleoptera: Coccinellidae).

To determine if differences in life history parameters contribute to native species exclusion, immature development times, larval survivorship, reproductive life history parameters, and age-specific life tables were determined for two populations (eastern United States and western United States) of ninespotted lady beetles (Coccinella novemnotata Herbst) and one population of sevenspotted lady beetles (Coccinella septempunctata L.). Developing larvae were provided an ad libitum diet of pea aphids (Acyrthosiphon pisum Harris) at a constant temperature of 25°C. The first and fourth larval stadia of C. novemnotata were significantly longer than that of C. septempunctata, as was their total development time from egg to newly eclosed adult. Stage-specific developmental mortality was low for both species and did not exceed 7% for the entire development period. The preoviposition period of the two C. novemnotata populations was significantly shorter (15-20%) than that of C. septempunctata. C. novemnotata from both locations laid significantly fewer total eggs than C. septempunctata (34-40% fewer) over the 31-d test period, and also fewer eggs per day (37-43% fewer). The net reproductive rate of the C. novemnotata populations was 42-50% lower than that of C. septempunctata as was C. novemnotata's intrinsic rate of natural increase (rm: 0.1716 and 0.1840 vs. 0.1959 for western and eastern C. novemnotata and C. septempunctata, respectively).

Aphid facultative symbionts reduce survival of the predatory lady beetle Hippodamia convergens

BackgroundNon-essential facultative endosymbionts can provide their hosts with protection from parasites, pathogens, and predators. For example, two facultative bacterial symbionts of the pea aphid (Acyrthosiphon pisum), Serratia symbiotica and Hamiltonella defensa, protect their hosts from parasitism by two species of parasitoid wasp. Previous studies have not explored whether facultative symbionts also play a defensive role against predation in this system. We tested whether feeding on aphids harboring different facultative symbionts affected the fitness of an aphid predator, the lady beetle Hippodamia convergens.ResultsWhile these aphid faculative symbionts did not deter lady beetle feeding, they did decrease survival of lady beetle larvae. Lady beetle larvae fed a diet of aphids with facultative symbionts had significantly reduced survival from egg hatching to pupation and therefore had reduced survival to adult emergence. Additionally, lady beetle adults fed aphids with facultative symbionts were significantly heavier than those fed facultative symbiont-free aphids, though development time was not significantly different.ConclusionsAphids reproduce clonally and are often found in large groups. Thus, aphid symbionts, by reducing the fitness of the aphid predator H. convergens, may indirectly defend their hosts’ clonal descendants against predation. These findings highlight the often far-reaching effects that symbionts can have in ecological systems.

Tracing prey origins, proportions and feeding periods for predatory beetles from agricultural systems using carbon and nitrogen stable isotope analyses

Predatory beetles are an important component of the natural enemy complex that preys on insect pests such as aphids within agroecosystems. Tracing diet origins and movement of natural enemies aids understanding their role in the food web and informs strategies for their effective conservation. Field sampling and laboratory experiments were carried out to examine the changes of carbon and nitrogen stable isotope ratios (δ13C and δ15N) among crops (cotton and maize), pests (cotton and maize aphids), and between wing and abdomen of predatory beetles, Propylea japonica, and to test the hypothesis that prey origins, proportions and feeding periods of the predatory beetles can be deduced by this stable isotope analysis. Results showed that the δ13C values both in wing and abdomen of adult P. japonica were changing from a C3- to a C4-based diet of aphids reared on maize or cotton, respectively; the isotope ratio of their new C4 substrates were detectable within 7days and the δ15N values began to reflect their new C4 substrates within 3days. The relationship between δ13C and δ15N values of P. japonica adults in wing or abdomen and diets of aphids from a C3-based resource transitioning to a C4-based resource were described best in linear or quadratic equations. Results suggest that integrative analysis of δ13C and δ15N values can be regarded as a useful method for quantifying to trace prey origins, proportions of diets and feeding periods of natural enemies. The results can provide quantifying techniques for habitat management of natural enemies.