Selection of aphid prey by a generalist predator: do prey chemical defences matter?

1. For predators, prey selection should maximise nutrition and minimise fitness costs. In the present study, it was investigated whether a generalist predator [Chrysoperla carnea (Stephens) lacewing larvae] rejected harmful, chemically‐defended prey [Brevicoryne brassicae (Linnaeus) aphids] when non‐defended prey [Myzus persicae (Sulzer) aphids] were available. 2. It was tested: (i) whether consuming different prey species affects predator mortality; (ii) whether naïve predators reject chemically‐defended prey while foraging when non‐defended prey are available; (iii) whether the relative abundance of each prey affects the predator's prey choice; and (iv) whether predators learn to avoid consuming chemically‐defended prey after exposure to both prey species. 3. Consumption of B. brassicae yielded greater C. carnea mortality than M. persicae consumption, but naïve C. carnea did not reject B. brassicae in favour of M. persicae during foraging. When presented at unequal abundances, naïve predators generally consumed each aphid species according to their initial relative abundance, although, predation of non‐defended prey was less than expected when defended prey were initially more abundant, indicating a high consumption of B. brassicae impeded M. persicae consumption. With experience, C. carnea maintained predation of both aphid species but consumed more M. persicae than B. brassicae, indicating a change in behaviour. 4. Although prey choice by C. carnea may change with experience of available prey, prey chemical defences do not appear to influence prey choice by naïve predators. This inability to avoid harmful prey could facilitate wider, indirect interactions. Myzus persicae may benefit where high consumption of B. brassicae hinders predators in the short term, and in the long term, increases predator mortality.     

Associational resistance or susceptibility: the indirect interaction between chemically‐defended and non‐defended herbivore prey via a shared predator

Many organisms possess chemical defences against their natural enemies, which render them unpalatable or toxic when attacked or consumed. These chemically‐defended organisms commonly occur in communities with non‐ or less‐defended prey, leading to indirect interactions between prey species, mediated by natural enemies. Although the importance of enemy‐mediated indirect interactions have been well documented (e.g. apparent competition), how the presence of prey chemical defences may affect predation of non‐defended prey in terrestrial communities remains unclear. Here, an experimental approach was used to study the predator‐mediated indirect interaction between a chemically‐defended and non‐defended pest aphid species. Using laboratory‐based mesocosms, aphid community composition was manipulated to include chemically‐defended (CD) aphids Brevicoryne brassicae, non‐defended (ND) aphids Myzus persicae or a mixed assemblage of both species, on Brassica oleracea cabbage plants, in the presence or absence of a shared predator (Chrysoperla carnea larvae). Aphid population growth rates, aphid distributions on host plants and predator growth rates were measured. In single‐species treatments, C. carnea reduced M. persicae population growth rate, but had no significant impact on B. brassicae population growth rate, suggesting B. brassicae chemical defences are effective against C. carnea. Chrysoperla carnea had no significant impact on either aphid species population growth rate in mixed‐species treatments. Myzus persicae (ND) therefore experienced reduced predation in the presence of B. brassicae (CD) through a predator‐mediated indirect effect. Moreover, predator growth rates were significantly higher in the M. persicae‐only treatments than in either the B. brassicae‐only or mixed‐species treatments, suggesting predation was impaired in the presence of B. brassicae (CD). A trait‐mediated indirect interaction is proposed, consistent with associational resistance, in which the predator, upon incidental consumption of chemically‐defended aphids is deterred from feeding, releasing non‐defended aphids from predatory control.     

Prey‐mediated effects of glucosinolates on aphid predators

1. Plant resistance against herbivores can act directly (e.g. by producing toxins) and indirectly (e.g. by attracting natural enemies of herbivores). If plant secondary metabolites that cause direct resistance against herbivores, such as glucosinolates, negatively influence natural enemies, this may result in a conflict between direct and indirect plant resistance. 2. Our objectives were (i) to test herbivore‐mediated effects of glucosinolates on the performance of two generalist predators, the marmalade hoverfly (Episyrphus balteatus) and the common green lacewing (Chrysoperla carnea) and (ii) to test whether intraspecific plant variation affects predator performance. 3. Predators were fed either Brevicoryne brassicae, a glucosinolate‐sequestering specialist aphid that contains aphid‐specific myrosinases, or Myzus persicae, a non‐sequestering generalist aphid that excretes glucosinolates in the honeydew, reared on four different white cabbage cultivars. Predator performance and glucosinolate concentrations and profiles in B. brassicae and host‐plant phloem were measured, a novel approach as previous studies often measured glucosinolate concentrations only in total leaf material. 4. Interestingly, the specialist aphid B. brassicae selectively sequestered glucosinolates from its host plant. The performance of predators fed this aphid species was lower than when fed M. persicae. When fed B. brassicae reared on different cultivars, differences in predator performance matched differences in glucosinolate profiles among the aphids. 5. We show that not only the prey species, but also the plant cultivar can have an effect on the performance of predators. Our results suggest that in the tritrophic system tested, there might be a conflict between direct and indirect plant resistance.     

Suitability of Different Prey Aphids on the Growth,Development and Reproduction of <Emphasis Type="Italic">Chrysoperla zastrowi sillemi</Emphasis> (Esben-Petersen) (Chrysopidae: Neuroptera)

The prey preference of polyphagous predator, green lacewing (Chrysoperla zastrowi sillemi (Esben-Petersen)) was evaluated against five prey aphids viz., mustard aphid (Lipaphis erysimi), green peach aphid (Myzus persicae), cabbage aphid (Brevicorynebrassicae), black bean aphid (Aphis craccivora), spirea aphid (Aphis spiraecola) of agriculture importance and compared with eggs of Corcyracephalonica (Stainton). Lacewing larvae preferred Myzus persicae most followed by Brevicorynebrassicae. The highest growth index (8.31), larval survival (94.50 %), larval weight (10.45 mg), pupal weight (8.78 mg), faster multiplication rate (0.051) and fecundity (183.4 per gravid female) of the predator were recorded on M. persicae. However, the chrysopid reared on Corcyra eggs performed best in all biological parameters and fitness, than on aphid preys. This study explores the possibilities of selecting the most suitable prey aphid species for its exploitation as supplement for mass multiplication of chrysopid during off-season or unavailability of Corcyra eggs.     

Impact of intraguild predation by adult Harmonia axyridis (Coleoptera: Coccinellidae) on Aphis glycines (Hemiptera: Aphididae) biological control in cage studies

The soybean aphid, Aphis glycines Matsumura, has become a principal arthropod pest of soybean in the U.S. since its first detection in 2000. This species threatens soybean production through direct feeding damage and virus transmission. A diverse guild of insect predators feeds on soybean aphid in Michigan including the exotic coccinellid Harmonia axyridis, the native gall midge Aphidoletes aphidimyza and the native lacewing Chrysoperla carnea. In addition to feeding on A. glycines some members of this guild may also engage in intraguild predation. These interactions may produce positive, negative, or neutral impacts on A. glycines biological control. We explored the impact of intraguild predation on soybean aphid population dynamics by comparing aphid populations in microcosms with either A. aphidimyza larvae or C. carnea larvae alone, with both a H. axyridis adult and either A. aphidimyza or C. carnea larvae, and without predators. When H. axyridis was present with larval A. aphidimyza or C. carnea, the lady beetle acted as an intraguild predator. However, intraguild feeding did not result in a release of aphid populations compared with microcosms containing only the intraguild and aphid prey. A similar result was found in field cages. Cages allowing large predators had reduced numbers of A. aphidimyza and C. carnea larvae but also significantly fewer aphids compared with predator exclusion cages. Thus, in both lab and field studies the direct impact of H. axyridis on A. glycines overcame its negative impact as an intraguild predator. Together, these studies indicate that while the exotic H. axyridis does act as an intraguild predator and may contribute to local declines in A. aphidimyza and C. carnea, it is also currently important in overall biological control of A. glycines.     

Intraguild Predation among the Hoverfly Episyrphus balteatus de Geer (Diptera: Syrphidae) and Other Aphidophagous Predators

Aphidophagous predators compete for the same prey species. During their foraging activity they frequently encounter heterospecific aphid predators. These situations can lead to intraguild predation and may disrupt biological control efforts against aphids where more than one predator species is present. We investigated the behavior of larvae of the hoverfly Episyrphus balteatus de Geer and its interaction with three other aphid predators: the ladybird Coccinella septempunctata L., the lacewing Chrysoperla carnea Stephens, and the gall midge Aphidoletes aphidimyza (Rondani). Interspecific interactions between predators were examined in arenas of different sizes and in the presence of extraguild prey. The outcome of interactions between E. balteatus larvae and the other predators depended predominantly on the relative body size of the competitors. Relatively large individuals acted as intraguild predators, while relatively smaller individuals became intraguild prey. Eggs and first- as well as second-instar larvae of E. balteatus were highly susceptible to predation by all other predators, whereas pupae of E. balteatus were preyed upon only by the larvae of C. carnea. Interactions between A. aphidimyza and E. balteatus were asymmetric and always favored the latter. Eggs and first- as well as second-instar larvae of E. balteatus sustained intraguild predation irrespective of the size of the arena or the presence of extraguild prey. However, the frequency of predation on third-instar larvae of E. balteatus was significantly reduced. This study indicated that the same species can be both intraguild predator and intraguild prey. It is suggested that combinations of predators must be carefully chosen for success in biological control of aphids.     

Implications of alternative prey on biocontrol of pests by arthropod predators in strawberry

A range of naturally occurring predator species or commercially produced predators can be used in biocontrol strategies for pests. However, multiple potential prey species or other alternative food sources are often present for predatory insects at any one time. The availability of this ‘alternative’ prey may affect specific pest control by predators and thus influence the release rates of predators required for economic pest control. Strawberry aphid (Chaetosiphon fragaefolii), western flower thrips (Frankliniella occidentalis) and European tarnished plant bug (Lygus rugulipennis) are important and damaging pests in strawberry. In this study, laboratory, glasshouse and field experiments were undertaken to assess the effects of the availability of multiple prey species on biocontrol of specific pests. Results indicated that two of the predators tested showed preferences for prey species such that biocontrol of a particular pest was often less effective when a combination of pest species was present than would have been expected from results of experiments with single prey species alone. The experiments indicated that Orius laevigatus preferred C. fragaefolii to F. occidentalis or to L. rugulipennis, and preferred L. rugulipennis to F. occidentalis. Chrysoperla carnea was shown to prefer C. fragaefolii to L. rugulipennis, and C. fragaefolii over F. occidentalis. Therefore, it is important to consider the effects of alternative prey on suppression of pest species when deciding on management strategies and release rates of predators.     

Predation rate and numerical response of Aphidoletes aphidimyza feeding on different densities of Aphis craccivora

Predation rate and numerical response are basic to any investigation of predator–prey relationships and key components in the selection of predators for biological control. The density-dependent predation rate and numerical response of Aphidoletes aphidimyza (Rondani) (Diptera: Cecidomyiidae) to varying densities (5, 10, 20, 40, 60 and 80) of third-instar Aphis craccivora (Koch) (Hemiptera: Aphididae), were studied in laboratory conditions [23±1°C, 70 ± 5% relative humidity (RH), and a photoperiod of 16:8 h L:D. Predation rate data were analysed using the age-stage, two-sex consumption rate software. Net consumption rate (C₀) increased by increasing prey density. The lowest and highest net consumption rates were 20.75 and 190.8 prey nymphs at densities of 5 and 80 A. craccivora. The transformation rate from prey population to predator offspring (Q_p) increased by increasing prey density. The reproductive numerical response, in terms of eggs laid, increased curvilinearly with increasing prey density. Females laid 121.375 ± 4.301 eggs when exposed to the highest prey density (80) and 52.5 ± 1.544 eggs at lowest prey density (5). It can be concluded that different densities of A. craccivora influenced the reproductive performance of A. aphidimyza in terms of predation rate and numerical response.     

Functional and numerical responses of Propylea dissecta (Col., Coccinellidae)

The functional response of a ladybeetle, Propylea dissecta, to increasing density of aphid, Aphis gossypii, was of the curvilinear shape depicting Holling's type II response with fourth instar larva being the most voracious stage when compared with adult male and female. Prey handling time by different predatory stages decreased from 65.45 to 8.72 min with increase in prey density from 25 to 800. The predator aggregation and high prey density reduces the searching efficiency of the predator. Area of discovery was highest (1.4437) when a single predator was searching at minimum aphid density (25) and lowest (0.0366) when eight predators were searching at a constant aphid density (200). Mutual interference and quest constants were 0.75 and 0.40, respectively. The reproductive numerical response, in terms of eggs laid, increased curvilinearly with prey density and female laid 70.5 ± 5.55 eggs when exposed to highest prey density (400) and 12.3 ± 0.79 eggs at lowest prey density (10). The similar shapes of both functional and reproductive responses indicate that both responses are interlinked and function simultaneously.     

The potential of predators in natural control of aphids in wheat: Results of a ten-year field study in two German landscapes

In the present study, we investigated the natural control of aphids by predators in wheat fields in a low (L) and high-input cropping region (H) of Germany during a 10-year period. Data for the statistical analyses were obtained from weekly after the start of aphid emergence. The mean annual aphid indices, calculated as the sum of Sitobion avenae (Fabr.), Rhopalosiphum padi (L.), Metopolophium dirhodum (Walk.)(Homoptera: Aphididae), were 30.4 and 81.5 × 103 aphid days per m2, for L and H, respectively. Nine predator fractions were analysed: Coccinella septempunctata L., adults (1) and larvae (2), Propylea quatuordecimpunctata (L.) (Coleoptera: Coccinellidae) adults (3) and larvae (4), syrphid larvae (mostly Episyrphus balteatus [De Geer] (Diptera: Syrphidae)) (5), Chrysoperla carnea Steph. (Neuroptera: Chrysopidae) larvae (6), and adult carabids (7), staphylinids (8) and spiders (9). The two sites were comparable in terms of the mean size of the overall predator community, expressed in predator units (PU): 4.9 PU/m2 (L) vs. 5.4 PU/m2 (H). Most predator fractions responded numerically to increasing aphid densities. The numerical response was strongest in syrphid larvae, scarcely detectable in adult coccinellids, and virtually non-existent in epigeic arthropods. Multiple regression models revealed indirect relationships between the weekly overall predator community densities (PU/m2) and individual predator fractions (individuals/m2) and absolute rates of aphid density increase (individuals/m2) one or two weeks after baseline. A site-independent reduction of the aphid density increase to nil (y = 0) was observed at 3.9 to 4.2 PU/m2. Consequently, the 2.7 times higher aphid density at H cannot be attributed to the presence of fewer predators or lower effects of the overall predator community or of any individual predator fraction.     

Do Chrysoperla carnea and Adalia bipunctata influence the spread of Cucurbit aphid‐borne yellows virus and its vector Aphis gossypii?

The effects of two aphidophagous predators, the larvae of Chrysoperla carnea and the adults of Adalia bipunctata, on the spread of Cucurbit aphid‐borne yellows virus (CABYV) transmitted by the cotton aphid Aphis gossypii were studied under semi‐field conditions. Aphids and natural enemies were released inside insect‐proof cages with a CABYV‐infected cucumber plant placed in the centre of the cage and surrounded by 48 healthy cucumber seedlings. The spatiotemporal dynamics of the virus and vector were evaluated in the short (7 days) and long term (14 days) in the presence and absence of each predator. The spatial analysis by distance indices methodology, together with other indices measuring the dispersal around a single focus, was used to assess the spatial pattern and the degree of association between the virus and vector. The presence of C. carnea larvae and A. bipunctata adults induced A. gossypii dispersal after 14 days but not after 7 days. The reduction of the initial aphid population established in the plant located in the centre of each cage was always higher for C. carnea than for A. bipunctata. There was some evidence that the natural enemies affected the spread of CABYV, though more so for C. carnea than for A. bipunctata. This study suggests an influence of both predators on the spread of the aphid, mainly in the long term, but only weak effect of predators in the spread of the viral disease was demonstrated.     

Microcosm studies on intraguild predation between female erigonid spiders and lacewing larvae and influence of single versus multiple predators on cereal aphids

Abstract: Intraguild predation between female erigonid spiders [Erigone atra (Blackwall) and Oedothorax apicatus (Blackwall), Araneae, Erigonidae] and lacewing larvae (second instar larvae of Chrysoperla carnea (Stephens), Neuropt., Chrysopidae) and interaction effects of predator combinations on cereal aphids were investigated in a microcosm system under laboratory conditions. The microcosm experiments were run for 7 days and consisted of 15wheat seedlings, 15 Sitobion avenae (F) (Hom., Aphididae) as start population, plus a female spider or a lacewing larva or a combination of a spider plus a lacewing larva. The mortality rate of lacewing larvae was significantly increased by 44 and 31% due to intraguild predation by female spiders of E. atra and O. apicatus in comparison with lacewing larvae that were kept alone. The final aphid numbers in the microcosms were significantly reduced by all single predator treatments (spiders, lacewing larvae) and the predator combinations in comparison with controls without predators. The predation effect on aphid populations due to both spider species was similar and not statistically different. An additive effect of the predator combinations ‘spider plus surviving lacewing larva’ was found for both spider species resulting in reduced aphid numbers compared with the single predator treatments. When the lacewing larva was killed by an E. atra female the effects on aphids were non‐additive, but aphid numbers were not statistically increased compared with the lacewing larva treatment. When the lacewing larva was killed by an O. apicatus female, the effects of spider and C. carnea larva were additive on aphid numbers. In the presence of additional prey (fruit flies and Collembola) intraguild predation was not found and E. atra females had no significant effect on the survival of lacewing larvae. In addition, E. atra females had no significant effect on aphid numbers in the presence of fruit flies and Collembola, but in combination with a lacewing larva that survived, a significantly greater reduction of the aphid population was observed compared with the lacewing larva treatment. The body mass of lacewing larvae at the end of the experiment was not statistically influenced by the presence or absence of an E. atra female.     

Determining the effects of life stage,shared prey density and host plant on intraguild predation of a native lacewing (<Emphasis Type="Italic">Chrysoperla carnea</Emphasis>) by an invasive coccinellid (<Emphasis Type="Italic">Harmonia axyridis</Emphasis>)

Negative impacts of non-native Harmonia axyridis (Pallas) on members of the native aphid enemy guild have been widely hypothesised but mainly only assessed with other coccinellid species, and mostly in small experimental arenas. Here we investigated the interactions between H. axyridis and Chrysoperla carnea Stephens larvae. In small-scale (Petri dish) arenas 2nd-instar C. carnea were at risk of predation from larval (2nd and 4th-instar) and adult (male and female) H. axyridis while 3rd-instar C. carnea were only at minimal risk from 4th-instar and adult female H. axyridis. Plant species, aphid species and aphid density did not affect intraguild predation of 2nd-instar C. carnea by 4th-instar and adult H. axyridis in mesocosm experiments. Chrysoperla carnea consumed similar numbers of Megoura viciae Buckton, Aphis fabae Scop. and Acyrthosiphon pisum Harris aphids while H. axyridis consumed fewer M. viciae than the other two species. The greatest suppression of A. pisum was achieved in treatments with both C. carnea and H. axyridis. Life stage and the sex of H. axyridis as well as the life stage of C. carnea are important variables affecting intraguild predation and these attributes should be considered when assessing the potential threat of other potentially invasive alien predators.     

Effect of temperature on the functional response of Adalia bipunctata to Myzus persicae

The effect of temperature on the functional response of female adults of the two-spot ladybird, Adalia bipunctata L. (Coleoptera: Coccinellidae) was examined in petri dish arenas containing sweet pepper leaves infested with different densities of the green peach aphid, Myzus persicae (Sulzer) (Hemiptera: Aphididae). The predator showed a type II functional response at three tested temperatures ranging from 19°C to 27°C. The theoretical maximum number of prey captured by the predator increased with temperature. Based on the random predator equation, the estimated attack rates ranged from 0.13 h^?1 at 19°C to 0.35 h^?1 at 27°C on a leaf area of 20–25 cm². There was no significant difference between the attack rates of the predator at 23°C and 27°C. Handling time significantly decreased as temperature increased from 19°C (0.39 h) to 27°C (0.24 h). This study shows that A. bipunctata displays high predation rates on M. persicae for a wide range of temperatures, indicating its potential for augmentative releases against this aphid pest. The limitations of the predictions generated by functional response experiments are discussed.     

Aggregation of polyphagous predators in response to multiple prey: ladybirds (Coleoptera: Coccinellidae) foraging in alfalfa

The spatial distribution of polyphagous predators may often reflect the integration of aggregative responses to local densities of multiple species of prey, and as such may have consequences for the indirect linkages among the prey sharing these predators. In a factorial field experiment in which we manipulated local prey densities within a field of alfalfa in Utah (USA), we tested whether aphidophagous ladybirds would aggregate not only in response to their primary aphid prey, but also in response to an abundant alternative prey, the alfalfa weevil (Hypera postica [Gyllenhal]). Native North American ladybirds (primarily Hippodamia convergens Guerin and H. quinquesignata quinquesignata [Kirby]) responded only to spatial variation in aphid density. In contrast, the introduced ladybird, Coccinella septempunctata L., aggregated also at local concentrations of the weevil late in the experiment when weevil density was high and aphid density was relatively low throughout all experimental plots. The results support the hypothesis that C. septempunctata is more responsive than are native ladybirds to the availability of alternative prey in alfalfa, which may account in part for the displacement of native ladybirds from alfalfa by the introduced species as aphid numbers have declined. The differing responses of the native and introduced ladybirds to spatial patterns of the alternative prey underscore the importance of extending the study of predator aggregation to understand better how polyphagous predators distribute themselves in response to spatial patterns of multiple species of potential prey.     

Influence of intraguild predation among generalist insect predators on the suppression of an herbivore population

We evaluated the influence of intraguild predation among generalist insect predators on the suppression of an herbivore, the aphid Aphis gossypii, to test the appropriateness of the simple three trophic level model proposed by Hairston, Smith, and Slobodkin (1960). We manipulated components of the predator community, including three hemipteran predators and larvae of the predatory green lacewing Chrysoperla carnea, in field enclosure/exclosure experiments to address four questions: (1) Do generalist hemipteran predators feed on C. carnea? (2) Does intraguild predation (IGP) represent a substantial source of mortality for C. carnea? (3) Do predator species act in an independent, additive manner, or do significant interactions occur? (4) Can the experimental addition of some predators result in increased densities of aphids through a trophic cascade effect? Direct observations of predation in the field demonstrated that several generalist predators consume C. carnea and other carnivorous arthropods. Severely reduced survivorship of lacewing larvae in the presence of other predators showed that IGP was a major source of mortality. Decreased survival of lacewing larvae was primarily a result of predation rather than competition. IGP created significant interactions between the influences of lacewings and either Zelus renardii or Nabis predators on aphid population suppression. Despite the fact that the trophic web was too complex to delineate distinct trophic levels within the predatory arthropod community, some trophic links were sufficiently strong to produce cascades from higher-order carnivores to the level of herbivore population dynamics: experimental addition of either Z. renardii or Nabis predators generated sufficient lacewing larval mortality in one experiment to release aphid populations from regulation by lacewing predators. We conclude that intraguild predation in this system is wide-spread and has potentially important influences on the population dynamics of a key herbivore.     

Amphipod (Gammarus minus) responses to predators and predator impact on amphipod density

Recent theoretical work suggests that predator impact on local prey density will be the result of interactions between prey emigration responses to predators and predator consumption of prey. Whether prey increase or decrease their movement rates in response to predators will greatly influence the impact that predators have on prey density. In stream systems the type of predator, benthic versus water-column, is expected to influence whether prey increase or decrease their movement rates. Experiments were conducted to examine the response of amphipods (Gammarus minus) to benthic and water-column predators and to examine the interplay between amphipod response to predators and predator consumption of prey in determining prey density. Amphipods did not respond to nor were they consumed by the benthic predator. Thus, this predator had no impact on amphipod density. In contrast, amphipods did respond to two species of water-column predators (the predatory fish bluegills, Lepomis macrochirus, and striped shiners, Luxilus chrysocephalus) by decreasing their activity rates. This response led to similar positive effects on amphipod density at night by both species of predatory fish. However, striped shiners did not consume many amphipods, suggesting their impact on the whole amphipod “population” was zero. In contrast, bluegills consumed a significant number of amphipods, and thus had a negative impact on the amphipod “population”. These results lend support to theoretical work which suggests that prey behavioral responses to predators can mask the true impact that predators have on prey populations when experiments are conducted at small scales. Received: 21 March 1997 / Accepted: 15 December 1997     

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.     

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.     

Prey‐mediated changes in the selectivity of the predator Macrolophus pygmaeus (Heteroptera: Miridae)

When foraging in communities with mixed prey, generalist predators may be confronted with prey species that differ in quality, size and mobility and interact with one another. To examine prey selection, predation by Macrolophus pygmaeus (Heteroptera: Miridae) was recorded by providing a diet of either one or two prey species of Myzus persicae (third‐instar nymphs), Aphis gossypii (fourth‐instar nymphs), Trialeurodes vaporariorum (third‐instar nymphs) and Ephestia kuehniella (eggs). In the experiments, prey mobility, prey quality and prey biomass were considered. The biomass consumed by the predator was dependent on the combination of prey species and the quantity of biomass offered. In choice experiments with diets mixed of two prey species at equal densities, the predation to A. gossypii was significantly reduced in the presence of E. kuehniella but the rate of consumption of M. persicae, T. vaporariorum and E.kuehniella was not significantly affected by the coexistence of any other species in the mixed prey diet. When equal amounts of biomass from two prey species were provided in combination, the total consumed biomass was significantly reduced in the mixed prey diets composed of E. kuehniella eggs and aphid nymphs. Thus, under the mixed‐prey situation, prey selection by predators may be affected by interactions among prey species differing in traits such as quality, mobility and size.