An immunological approach to quantify consumption of protein-tagged Lygus hesperus by the entire cotton predator assemblage

A new method for post-mortem quantification of predation on prey items marked with protein antigens is described. First, short-term protein marking retention tests were conducted on the targeted prey, immature Lygus hesperus Knight (Heteroptera: Miridae). Chicken IgG, rabbit IgG, or soy milk proteins were readily detectable by a suite of protein specific enzyme-linked immunosorbent assays (ELISA) on the L. hesperus. Then, predator gut content assays were conducted on chewing and piercing–sucking type predators that consumed a 3rd instar L. hesperus marked with rabbit IgG. The rabbit IgG gut content ELISA detected the marked prey in the vast majority of both types of predators for up to 24 h after feeding. Finally, field cage studies were conducted to quantify predation rates of the natural cotton predator assemblage on protein marked L. hesperus nymphs. Each 4th instar L. hesperus marked with rabbit IgG, chicken IgG, and soy milk was released into one of 360 field cages containing a cotton plant and the natural population of predators. After 7 h, each caged plant was pulled from the field, the number of predaceous arthropods in each cage were tallied, and each individual predator was assayed for the presence of marked prey by a suite of protein-specific ELISAs. A procedural error with the soy mark application negated the anti-soy ELISA data, but the anti-rabbit IgG and anti-chicken IgG ELISAs pinpointed exactly which predators preyed on the IgG marked nymphs. The protein-specific gut ELISAs revealed that various members of Araneae, Heteroptera, and Coleoptera were the most common predators of the marked prey items. In all, 74 predation events were recorded in the guts of the 556 predators encountered in the field cages. Of these 26, 23, and 14 marked individuals were eaten by various members of Araneae, Heteroptera, and Coleoptera, respectively. This study verifies that prey immunomarking is a simple, versatile, and effective method for quantifying predation rates on L. hesperus.     

Factors affecting detectability of prey DNA in the gut contents of invertebrate predators: a polymerase chain reaction-based method

This study aimed to determine factors that influence the detection of DNA of Plutella xylostella L. (Lepidoptera: Plutellidae) in the gut contents of arthropod predators when the polymerase chain reaction is used to amplify a diagnostic fragment of the gene coding for cytochrome oxidase subunit I. The effects of temperature, time since feeding, subsequent food intake, sex, weight, and species of predator on prey detectability were studied in the laboratory. Three types of predator were studied: the spider Venator spenceri Hogg. (Araneae: Lycosidae), a bug with sucking mouthparts, Nabis kinbergii (Reuter) (Heteroptera: Nabidae), and a coccinellid with chewing mouthparts, Hippodamia variegata (Goeze) (Coleoptera: Coccinellidae). In all experiments, the detectability of prey DNA was negatively correlated with time post‐feeding. The duration of detectability differed among the predator species. The time calculated for median detection success at 20 °C ranged from 49.6 h in V. spenceri to 36.1 h in N. kinbergii and 17.1 h in H. variegata. In H. variegata, but not in V. spenceri, the rate of detection decreased with increasing temperature. Subsequent food intake did not affect the detectability of DNA of P. xylostella in V. spenceri. In H. variegata, sex and weight of the predator did not influence detection of prey DNA. In addition, this study uncovered potential sources of error caused by detection of prey DNA following secondary cannibalistic and intraguild predation. The results provide essential information for the interpretation of prey detection data from field‐collected predators’ gut contents.     

Development of an immunological technique for identifying multiple predator–prey interactions in a complex arthropod assemblage

A simplified but highly effective approach for the post‐mortem evaluation of predation on several targeted members of an arthropod assemblage that does not require the development of pest‐specific enzyme‐linked immunosorbent assay (ELISA) (e.g. pest‐specific monoclonal antibodies) or PCR assays (DNA primers) is described. Laboratory feeding studies were conducted to determine if predation events could be detected from predators that consumed prey marked with foreign protein. I determined that large and small rabbit immunoglobulin G (IgG)‐marked prey can be detected by a rabbit‐IgG‐specific ELISA in the guts of chewing and piercing–sucking type predators. I then conducted multifaceted inclusion and exclusion field cage studies to qualify the degree of interguild and intraguild predation occurring among a complex arthropod assemblage during four separate light phase treatments. The field cages contained an arthropod assemblage consisting of 11 or 12 species of predaceous arthropods and three pest species. The three pests introduced into the cages included third instar Trichoplusia ni marked with rabbit IgG, third instar Lygus hesperus marked with chicken IgG and Pectinophora gossypiella sentinel egg masses. The inclusion cages allowed foraging fire ants, Solenopis xyloni, to freely enter the cages while the exclusion cages contained barriers that prevented ant entry. The results obtained using the conventional inclusion/exclusion field cage methodology revealed that there was substantial interguild and intraguild predation occurring on the majority of the arthropods in the assemblage, particularly in those cages that included ants. I then precisely identified which predators in the assemblage were feeding on the three targeted pests by conducting three post‐mortem gut content analyses on each individual predator (1503 individuals) in the assemblage. Specifically, P. gossypiella egg predation events were detected using an established P. gossypiella‐egg‐specific ELISA, and third instar T. ni and L. hesperus predation events were detected using rabbit‐IgG‐specific and chicken‐IgG‐specific ELISAs, respectively. Generally, the gut ELISAs revealed that Collops vittatus, Spanagonicus albofasciatus and Geocoris punctipes readily preyed on P. gossypiella eggs; Nabis alternatus, Zelus renardii and spiders (primarily Misumenops celer) readily preyed on marked L. hesperus nymphs, and spiders, S. albofasciatus and N. alternatus readily preyed on T. ni larvae. Furthermore, the cage methods and the post‐mortem predator gut ELISAs revealed very few distinctive patterns of predation with regard to the light cycle the assemblage was exposed to.     

Light dependency of life trails,reproduction, locomotion,and predation in the polyphagous ladybird Hippodamia variegata

Light is regarded a key environmental cue influencing biological, physiological, and behavioral characteristics in insects. We compared the development, reproduction, locomotion, and predation ability of the predatory ladybird Hippodamia variegata (Goeze) (Coleoptera: Coccinellidae) under various photoperiods, light intensities, and light wavelengths. The results indicated long daylight, high light intensity, and particular colors light (blue, green, and yellow) could benefit H. variegata especially in shortening the period of immature development, increasing mating frequency (shorter mating and pre‐oviposition periods), higher fecundity, and a higher proportion of eggs hatched. Average locomotion speed and prey consumption rate of H. variegata increased with prolonged day length and increased light intensity. However, very high intensity of light could inhibit predation rates. Furthermore, green and yellow wavelength conditions increased locomotion speed of H. variegata, and the number of prey consumed increased with increased wavelength. The present study not only revealed significant influences of light conditions on the development and fertility of H. variegata, it also provided sufficient empirical data to improve the efficiency of mass rearing and field releases of this predatory ladybird by regulation of light conditions during biological control applications.     

An immunological approach to distinguish arthropod viviphagy from necrophagy

Scavenging activity of predators inhabiting agroecosystems has not been thoroughly investigated. Understanding the prevalence of necrophagy in predators is paramount to determining the effectiveness of biological control agents. A molecular predator gut content assay is described that can differentiate necrophagy from viviphagy. Cadaver sweetpotato whitefly, Bemisia tabaci (Gennadius) (Hemiptera: Aleyrodidae) and green lacewing, Chrysoperla rufilabris Burmeister (Neuroptera: Chrysopidae) serving as targeted prey items were marked with rabbit immunoglobulin G (IgG) protein and live prey items were marked with chicken IgG, respectively. The marked prey items were fed to convergent lady beetles, Hippodamia convergens Guérin-Méneville (Coleoptera: Coccinellidae) and soft-winged flower beetles, Collops vittatus (Say) (Coleoptera: Melyridae). The frequency of detection of the protein-marked prey items in the gut of the predaceous beetles was assessed at 0, 3, 6, 12, 24 and 48 h after feeding using a rabbit-IgG-specific or chicken-IgG-specific enzyme-linked immunosorbent assay (ELISA). Each IgG-specific ELISA detected the presence of the marker proteins in the gut of 90 % of the predators up to 12 h after prey consumption. A laboratory feeding study was also conducted to determine the propensity that each predator species engages in viviphagy and necrophagy. The laboratory feeding observations revealed that C. vittatus prefer carrion prey items. Finally, the laboratory observations of necrophagy were confirmed in a field study where C. vittatus was observed, directly and indirectly, feeding on H. convergens carcasses. The methodologies described here are useful for future studies on various aspects of insect predation.     

Fresh,frozen or fake: A comparison of predation rates measured by various types of sentinel prey

Arthropod predators and parasitoids support the health and functioning of the world's ecosystems, most notably by supplying biological control services to agricultural landscapes. Quantifying the impact that these organisms have on their prey can be challenging, as direct observation and measurement of arthropod predation is difficult. The use of sentinel prey is one method to measure predator impact; however, despite widespread use, few studies have compared predation on different prey types within a single experiment. This study evaluated the predation rates on four sentinel prey items in grass and wheat fields in south-east Queensland, Australia. Attack rates on live and dead Helicoverpa armigera eggs, and dead H. armigera larvae and artificial plasticine larvae, were compared and the predators that were attracted to each prey type were documented with the use of field cameras. There was no significant difference in predation rates between sentinel eggs, while dead larvae were significantly more attacked than artificial larvae. Prey were attacked by a diverse range of predators, including ants, beetles, various nymph and juvenile insects and small mammals. Different predators were active in grass and crop fields, with predator activity peaking around dawn and dusk. The same trends were observed within and between the two habitats studied, providing a measure of confidence in the sentinel prey method. A range of different sentinel prey types could be suitable for use in most comparative studies; however, each prey type has its own benefits and limitations, and these should be carefully evaluated to determine which is most suitable to address the research questions.     

Predation of Colorado potato beetle eggs by a polyphagous ladybeetle in the presence of alternate prey: potential impact on resistance evolution

The influence of prey choice on the predation of a target prey item by a polyphagous insect predator was investigated in field plot studies. The target prey consisted of eggs of the Colorado potato beetle (CPB), Leptinotarsa decemlineata Say (Coleoptera: Chrysomelidae), and the predator was the 12‐spotted ladybeetle, Coleomegilla maculata Lengi (Coleoptera: Coccinellidae). Eggs of the European corn borer (ECB), Ostrinia nubilalis Hübner (Lepidoptera: Pyralidae), and nymphs and adults of the green peach aphid, Myzus persicae Sulzer (Homoptera: Aphididae), comprised the alternative prey choices. The objectives of these studies were to: (1) examine predation in a multiprey scenario likely to occur in an agroecosystem, and (2) use the data to simulate the impact of predator‐induced mortality on the evolution of resistance to Bt‐transgenic plants in the target herbivore. Simulations of the rate of resistance evolution were carried out using a deterministic genetic model. Experiments were performed using potato field plots planted in a manner reflecting a 25% or 50% non‐transgenic refuge. CPB eggs were infested so as to mimic the densities of resistant and susceptible populations that might occur in commercial Bt‐transgenic plantings. Densities of predators and alternate prey species were chosen to represent those that might typically occur in potato crops in the eastern USA. Simulation results indicated that when ECB eggs were present, predation on CPB eggs either became inversely spatially density‐dependent, or increased significantly in a density‐dependent manner. When aphids were present, predation became positively density‐dependent. Model simulations predicted that ECB egg presence is beneficial, in that resistance was delayed by up to 40 pest generations (as compared to the scenario with CPB as the only prey), while aphid presence accelerated resistance evolution by 18 generations. Results suggest that resistance management strategies should take into account the composition of prey species available to generalist predators typically present, so as to best delay pest adaptation to Bt‐toxins.     

Predatory response of Xylocoris flavipes to bruchid pests of stored food legumes

Biological control may provide an affordable and sustainable option for reducing losses to pest Bruchidae in stored food legumes, a crucial source of human dietary protein. Previous investigations have focused primarily on the role of parasitism in bruchid biological control, while the potential of generalist predators has been comparatively unexplored. The true bug Xylocoris flavipes (Reuter) (Heteroptera: Anthocoridae) exhibited a Type II functional response to the majority of cosmopolitan bruchid species evaluated when data were fit to Holling's disc equation. A negative correlation was detected between mean pest species body weight and rate of predation. The rate of attack on adult prey was quite low but fairly consistent, with the larger‐sized female predators generally more effective. The eggs and neonate larvae of Acanthoscelides obtectus Say (Coleoptera: Bruchidae) were the only accessible immature stages among all prey species examined; predation on A. obtectus eggs and larvae was higher than on any adult bruchids. Mean predator kill of A. obtectus immature stages was 40 first instars or 10–20 eggs per 24‐h interval. Further investigation of the biological control potential of X. flavipes against pest Bruchidae is merited due to the predator's ability to kill adult stages of all prey species evaluated.     

A false‐positive food chain error associated with a generic predator gut content ELISA

Conventional prey‐specific gut content ELISA (enzyme‐linked immunosorbent assay) and PCR (polymerase chain reaction) assays are useful for identifying predators of insect pests in nature. However, these assays are prone to yielding certain types of food chain errors. For instance, it is possible that prey remains can pass through the food chain as the result of a secondary predator (hyperpredator) consuming a primary predator that had previously consumed the pest. If so, the pest‐specific assay will falsely identify the secondary predator as the organism providing the biological control services to the ecosystem. Recently, a generic gut content ELISA was designed to detect protein‐marked prey remains. That assay proved to be less costly, more versatile, and more reliable at detecting primary predation events than a prey‐specific PCR assay. This study examines the chances of obtaining a ‘false positive’ food chain error with the generic ELISA. Data revealed that the ELISA was 100% accurate at detecting protein‐marked Lygus hesperus Knight (Hemiptera: Miridae) remains in the guts of two (true) primary predators, Hippodamia convergens Guérin‐Méneville (Coleoptera: Coccinellidae) and Collops vittatus (Say) (Coleoptera: Melyridae). However, there was also a high frequency (70%) false positives associated with hyperpredators, Zelus renardii Kolenati (Hemiptera: Reduviidae), that consumed a primary predator that possessed protein‐marked L. hesperus in its gut. These findings serve to alert researchers that the generic ELISA, like the PCR assay, is susceptible to food chain errors.     

Does dimethyl sulfoxide increase protein immunomarking efficiency for dispersal and predation studies?

Marking biological control agents facilitates studies of dispersal and predation. This study examines the effect of a biological solvent, dimethyl sulfoxide (DMSO), on retention of immunoglobulin G (IgG) protein solutions applied to Diorhabda carinulata (Desbrochers) (Coleoptera: Chrysomelidae), an important biological control agent of saltcedar, either internally by feeding them protein‐labeled foliage or externally by immersing them in a protein solution. In addition, we determined whether internally or externally marked DMSO‐IgG labels could be transferred via feeding from marked D. carinulata to its predator, Perillus bioculatus (Fabricius) (Heteroptera: Pentatomidae). The presence of rabbit and chicken IgG proteins was detected by IgG‐specific enzyme‐linked immunosorbent assays (ELISA). DMSO‐IgG treatments showed greater label retention than IgG treatments alone, and this effect was stronger for rabbit IgG than for chicken IgG. Fourteen days after marking, beetles immersed in rabbit IgG showed 100% internal retention of label, whereas beetles immersed in chicken IgG showed 65% internal retention. Immersion led to greater initial (time 0) label values, and longer label retention, than feeding beetles labeled foliage. The DMSO‐IgG label was readily transferred to P. bioculatus after feeding on a single marked prey insect. This investigation shows that addition of DMSO enhances retention of IgG labels, and demonstrates that protein marking technology has potential for use in dispersal and predator–prey studies with D. carinulata. Moreover, our observation of P. bioculatus feeding on D. carinulata is, to our knowledge, a new predator–prey association for the stink bug.     

Prey to predator transfer of enriched 15N-contents: basic laboratory data for predation studies using 15N as marker

As an alternative to methods currently used to study predation under field conditions, we propose to mark prey with ¹⁵N, and to subsequently trace this label in the food chain. Preliminary laboratory work to develop this method is presented. The ¹⁵N‐content of polyphagous predators that have ingested ¹⁵N‐marked aphids was analysed with respect to: time after ingestion, the number of ingested ¹⁵N‐aphids, ingestion of additional non‐marked prey, and predator size. Increased ¹⁵N‐contents were detected in solid feeders [Platynus dorsalis (Pontopiddan), Coleoptera: Carabidae], as well as in fluid feeders [Erigone atra (Blackwall), Araneae: Linyphiidae] up to 11 days after ingestion. The increased ¹⁵N‐levels were constant over time from a few days after ¹⁵N‐ingestion onwards, and correlated with the number of ingested ¹⁵N‐aphids. The ingestion of additional non‐marked prey had no statistically significant influence on the predators’¹⁵N‐contents. The ¹⁵N‐contents of carabid species with varying biomasses could be compared directly. Our results are compared with literature data of other methods (e.g., ELISA).     

Two common invertebrate predators show varying predation responses to different types of sentinel prey

Sentinel prey (an artificially manipulated patch of prey) are widely used to assess the level of predation provided by natural enemies in agricultural systems. Whilst a number of different methodologies are currently in use, little is known about how arthropod predators respond to artificially manipulated sentinel prey in comparison with predation on free‐living prey populations. We assessed how attack rates on immobilized (aphids stuck to cards) and artificial (plasticine lepidopteran larvae mimics) sentinel prey differed to predation on free‐moving live prey (aphids). Predation was assessed in response to density of the common invertebrate predators, a foliar‐active ladybird Harmonia axyridis (Coleoptera: Coccinellidae), and a ground‐active beetle Pterostichus madidus (Coleoptera: Carabidae). Significant increases in attack rates were found for the immobilized and artificial prey between the low and high predator density treatments. However, an increased predator density did not significantly reduce numbers of free‐living live aphids included in the mesocosms in addition to the alternate prey. We also found no signs of predation on the artificial prey by the predator H. axyridis. These findings suggest that if our assessment of predation had been based solely on the foliar artificial prey, then no increase in predation would have been found in response to increased predator density. Our results demonstrate that predators differentially respond to sentinel prey items which could affect the level of predation recorded where target pest species are not being used.     

Development and application of molecular gut‐content analysis to detect aphid and coccinellid predation by Harmonia axyridis (Coleoptera: Coccinellidae) in Italy

Despite their positive effect in reducing pest populations, exotic generalist predators sometimes become invasive and contribute to the displacement of indigenous species in the same trophic level. Although laboratory experiments have linked intraguild predation (IGP) to these interactions, field evidence and quantification of IGP are still lacking for most systems. The recent establishment of the exotic Harmonia axyridis (Pallas) (Coleoptera: Coccinellidae) in Italy raises concern about the detrimental effect that the ladybird could have on native coccinellids. Here we assessed, under laboratory conditions, the acceptability and suitability of eggs of 2 native ladybirds, Adalia bipunctata L. and Oenopia conglobata (L.), as prey items for H. axyridis larvae. Then we developed primers for molecular gut‐content analysis to detect predation by H. axyridis on the 2 ladybirds and on the aphid Eucallipterus tiliae L. Species‐specific 16S primers were developed for the 3 species and laboratory feeding trials were conducted to quantify the rate of prey DNA breakdown in the gut of H. axyridis. Moreover, to field evaluate primers, H. axyridis 4th instars (n = 132) were systematically collected from linden trees in northern Italy and screened for the presence of prey DNA. Seventy‐three percent and 7% of field collected H. axyridis were positive for aphid and coccinellid DNA, respectively. Predation upon aphid and A. bipunctata was lower than predicted if density dependent consumption was expected, while predation upon O. conglobata was significantly higher. Here, we provided the first evidence of IGP among feral populations of H. axyridis and indigenous ladybird beetles, occurring in Italy.     

Functional response of Chrysoperla carnea (Neuroptera: Chrysopidae) to Helicoverpa armigera (Lepidoptera: Noctuidae): Effect of prey and predator stages

Abstract Understanding predator–prey interactions has a pivotal role in biological control programs. This study evaluated the functional response of three larval instars of the green lacewing, Chrysoperla carnea (Stephens), preying upon eggs and first instar larvae of the cotton bollworm, Helicoverpa armigera Hübner. The first and second instar larvae of C. carnea exhibited type II functional responses against both prey stages. However, the third instar larvae of C. carnea showed a type II functional response to the first instar larvae of H. armigera, but a type III functional response to the eggs. For the first instar larvae of C. carnea, the attack rate on H. armigera eggs was significantly higher than that on the larvae, whereas the attack rate of the second instar C. carnea on H. armigera larvae was significantly higher than that on the eggs. For the third instar larvae of C. carnea, the attack rate on the larvae was 1.015 ± 0.278/h, and the attack coefficient on the eggs was 0.036 ± 0.005. The handling times of the third instar larvae on larvae and eggs were 0.087 ± 0.009 and 0.071 ± 0.001 h, respectively. The highest predation rate was found for the third instar larvae of C. carnea on H. armigera eggs. Results of this study revealed that the larvae of C. carnea, especially the third instar, had a good predation potential in controlling H. armigera eggs and larvae. However, for a comprehensive estimation of the bio‐control abilities of C. carnea toward H. armigera, further field‐based studies are needed.     

Foraging responses of Coccinella septempunctata,Hippodamia variegata and Chrysoperla carnea to changing in density of two aphid species

The successful use of predators in classical biocontrol programmes needs several background laboratory investigations, one of which is the evaluation of predator behavioural responses to changes in the density of their prey. The impact effect of the density of two prey species [Myzus persicae Sulzer and Aphis craccivora Koch (Hemiptera: Aphididae)] on the predation rates of third-instar Chrysoperla carnea Stephens (Chrysopidae: Neuroptera) and fourth-instar Coccinella septempunctata L. and Hippodamia variegata Goeze (Coccinellidae: Coleoptera) larvae was studied. Although prey species, predator species, prey density, and their interactions all had significant effects on the numbers of aphids consumed, the type of functional response did not vary, remaining a type II response in all treatments. However, the type II parameters differed among predator species on the same prey species, and for each predator species on the two prey species. Chrysoperla. carnea on M. persicae and H. variegata on A. craccivora were more voracious than other predators. In the context of functional response and biological control, the release of these predators, that show inverse density-dependent mortality, has to be started in early season to build up their population on low aphid densities and attack later high aphid populations.     

Protein marking reveals predation on termites by the woodland ant, <Emphasis Type="Italic">Aphaenogaster rudis</Emphasis>

Subterranean termites provide a major potential food source for forest-dwelling ants, yet the interactions between ants and termites are seldom investigated largely due to the cryptic nature of both the predator and the prey. We used protein marking (rabbit immunoglobin protein, IgG) and double antibody sandwich enzyme-linked immunosorbent assay (DAS-ELISA) to examine the trophic interactions between the woodland ant, Aphaenogaster rudis (Emery) and the eastern subterranean termite, Reticulitermes flavipes (Kollar). We marked the prey by feeding the termites paper treated with a solution of rabbit immunoglobin protein (IgG). Subsequently, we offered live, IgG-fed termites to ant colonies and monitored the intracolony distribution of IgG-marked prey. Laboratory experiments on the distribution of protein-marked termite prey in colonies of A. rudis revealed that all castes and developmental stages receive termite prey within 24 h. In field experiments, live, protein-marked termites were offered to foraging ants. Following predation, the marker was recovered from the ants, demonstrating that A. rudis preys on R. flavipes under field conditions. Our results provide a unique picture of the trophic-level interactions between predatory ants and subterranean termites. Furthermore, we show that protein markers are highly suitable to track trophic interactions between predators and prey, especially when observing elusive animals with cryptic food-web ecology. Received 19 January 2007; revised 23 March 2007; accepted 26 March 2007.     

Influence of intraguild predation between Episyrphus balteatus and Hippodamia variegata on their prey

Intraguild predation (IGP) is an interaction that frequently occurs in natural enemy communities, especially aphidophagous predators. This research investigated IGP intensity between Episyrphus balteatus De Geer (Diptera: Syrphidae), with Hippodamia variegata Goeze (Coleoptera: Coccinellidae). Five predator combinations including second and third larvae of H. variegata and third instar larvae of E. balteatus plus control treatment (totally six treatments) were tested. The effect of IGP on cotton aphid, Aphis gossypii Glover (Hemiptera: Aphididae) population density was investigated on sweet pepper seedlings under laboratory microcosms. In most combinations, the third instar larvae of E. balteatus alone reduced an A. gossypii population more efficiently than ladybird larvae and their combinations. Furthermore, IGP between third instar of E. balteatus and second larvae of H. variegata was asymmetrical; second instar H. variegata larvae were always the intraguild prey for third instar E. balteatus. The obtained result showed that outcome of IGP interaction on cotton aphid density was non-additive.     

Does nitrogen limitation promote intraguild predation in an aphidophagous ladybird?

Reciprocal intraguild predation occurs between the two aphidophagous ladybird beetles Coccinella septempunctata L. and Harmonia axyridis Pallas (Coleoptera: Coccinellidae). However, its direction is asymmetrical; H. axyridis generally acts as an intraguild predator, and C. septempunctata as an intraguild prey. According to Denno and Fagan's prediction that nitrogen shortages in predators may promote intraguild predation, it was hypothesized that growth of intraguild predator H. axyridis is more limited by nitrogen than that of intraguild prey C. septempunctata, and that H. axyridis growth is enhanced by feeding on C. septempunctata compared to feeding on aphids. To determine nitrogen‐limited growth in H. axyridis, the following two predictions were examined. First, it was predicted that the nitrogen content of H. axyridis would be higher than that of C. septempunctata when both feed on aphids. However, nitrogen content did not differ between the two ladybirds. Second, it was predicted that nitrogen‐use efficiency of H. axyridis would be lower than that of C. septempunctata. However, there was no significant difference between species. These results did not support the hypothesis that growth of H. axyridis is more limited by nitrogen than that of C. septempunctata. In addition, the present study showed that dry mass and nitrogen growth of H. axyridis were not enhanced, but rather decreased, by eating high‐nitrogen C. septempunctata, compared to eating low‐nitrogen aphids. Overall, the present study did not support the hypothesis that nitrogen shortages in predators may promote intraguild predation.     

Impact of predation on early stages of the armoured catfish Hoplosternum thoracatum (Siluriformes-Callichthyidae) and implications for the syntopic occurrence with other related catfishes in a neotropical multi-predator swamp

This study investigated the role of predators in preventing competitive exclusion among three closely related armoured catfishes (Callichthys callichthys, Hoplosternum littorale and H. thoracatum) that occur synthopically in multi-predator freshwater swamps of Suriname, South America. The potential impact of predation on armoured catfish was determined by combining laboratory measurements of predation rates on five early developmental stages of the armoured catfish H. thoracatum for 24 aquatic predators with field studies of the density of the predators in the swamps. The contribution of a particular predator to the total predation pressure on its prey was determined to a large extent by the density of the predator in the swamp. Seemingly innocuous predators with low or moderate predation rates in the laboratory may be extremely important in the swamps due to their high abundance. Small-sized omnivorous fishes and aquatic invertebrates were major predators of early developmental stages of armoured catfish. Both qualitative and quantitative ontogenetic changes in the predation pressure on armoured catfish were observed. Major predation on eggs, larvae and juveniles of H. thoracatum resulted from a different set of predators in each developmental stage of the prey. In all developmental stages of H. thoracatum the predation pressure involved several predator species and not a single, dominant predator. The potential predation pressure of the 24 predators taken together and the number of predators that were able to prey on H. thoracatum decreased sharply with increasing age (size) of the prey. Even if egg (nest) predation is prevented by the guarding male, the potential impact of the 24 predators on the populations of armoured catfish is large. Predation may account for the high mortality of H. thoracatum observed in the swamps. The high predation pressure on callichthyid catfishes may help to explain the coexistence of three closely related and morphologically quite similar armoured catfishes in Surinamese swamps.     

Efficacy of a Cladosporium sp. fungus against Helicoverpa armigera (Lepidoptera: Noctuidae), other insect pests and beneficial insects of cotton

A strain of the fungus Cladosporium sp. (RM16) from an egg of Helicoverpa armigera Hübner (Lepidoptera: Noctuidae) was assessed as a potential biocontrol agent for this pest. Pathogenicity of the fungus was tested against H. armigera eggs and larvae, cotton aphids (Aphis gossypii Glover; Homoptera: Aphididae), and silverleaf whitefly type B (Bemisia tabaci Gennadius; Hemiptera: Aleyrodidae). The pathogenicity of the fungus to the predatory red and blue beetles (Dicranolaius bellulus Guérin-Méneville; Coleoptera: Melyridae), transverse ladybird beetles (Coccinella transversalis Fabricius; Coleoptera: Coccinellidae), green lacewings (Mallada signatus Schneider; Neuroptera: Chrysopidae) and damsel bugs (Nabis kinbergii Reuter; Hemiptera: Nabidae), was also assessed in the laboratory. Fungus treatment resulted in failure to hatch of up to 64% of H. armigera eggs (compared with 11% in the controls) and mortality of 54% of first instar H. armigera larvae (compared with 5% in the controls). In contrast, it was not pathogenic to later instar H. armigera larvae. Cladosporium RM16 was also efficacious against the sap-sucking insect pests of cotton that were tested. No significant harmful effect of the fungus was found on any of the four beneficial predatory insects assessed in this study. Cladosporium RM16 has the potential as biological control agent to support integrated pest management in cotton farming systems, although this needs intensive study.