Biodiversity Loss following the Introduction of Exotic Competitors: Does Intraguild Predation Explain the Decline of Native Lady Beetles?

Exotic species are widely accepted as a leading cause of biodiversity decline. Lady beetles (Coccinellidae) provide an important model to study how competitor introductions impact native communities since several native coccinellids have experienced declines that coincide with the establishment and spread of exotic coccinellids. This study tested the central hypothesis that intraguild predation by exotic species has caused these declines. Using sentinel egg experiments, we quantified the extent of predation on previously-common (Hippodamia convergens) and common (Coleomegilla maculata) native coccinellid eggs versus exotic coccinellid (Harmonia axyridis) eggs in three habitats: semi-natural grassland, alfalfa, and soybean. Following the experiments quantifying egg predation, we used video surveillance to determine the composition of the predator community attacking the eggs. The extent of predation varied across habitats, and egg species. Native coccinellids often sustained greater egg predation than H. axyridis. We found no evidence that exotic coccinellids consumed coccinellid eggs in the field. Harvestmen and slugs were responsible for the greatest proportion of attacks. This research challenges the widely-accepted hypothesis that intraguild predation by exotic competitors explains the loss of native coccinellids. Although exotic coccinellids may not be a direct competitor, reduced egg predation could indirectly confer a competitive advantage to these species. A lower proportion of H. axyridis eggs removed by predators may have aided its expansion and population increase and could indirectly affect native species via exploitative or apparent competition. These results do not support the intraguild predation hypothesis for native coccinellid decline, but do bring to light the existence of complex interactions between coccinellids and the guild of generalist predators in coccinellid foraging habitats.     

Prey discrimination by a generalist coccinellid predator: effect of prey age or parasitism?

1. Patterns of prey discrimination by the generalist predatory coccinellid Coleomegilla maculata lengi Timb. (Coleoptera: Coccinellidae) were studied in relation to prey quality, under laboratory conditions. 2. Choice experiments were performed in which second‐ and fourth‐instar coccinellids had the choice between Trichoplusia ni (Lepidoptera: Noctuidae) eggs that were young or old, unparasitised or parasitised by Trichogramma evanescens Westwood (Hymenoptera: Trichogrammatidae). 3. Coleomegilla maculata larvae did not exhibit any preference for parasitised or unparasitised eggs at a similar stage of development but always preferred younger eggs, regardless of whether or not they were parasitised. Furthermore, the percentage of rejection was higher and handling time longer on the less preferred egg type. Pre‐imaginal development time, food intake to reach adulthood, and survival of coccinellid immatures were altered when coccinellid larvae were fed with parasitised and old unparasitised eggs. 4. These results indicate that C. maculata larvae select eggs based on their stage of development regardless of parasitism, and that prey quality of aged prey is lower. 5. Fourth‐instar coccinellid larvae spent less time in patches containing solely parasitised old eggs, and their level of exploitation was greatly reduced, compared with homogeneous patches containing unparasitised young eggs. This suggests that C. maculata larvae respond to variable patch quality by using flexible decision rules that reflect the payoff of the patch.     

Inundative release of coccinellid beetles into eucalypt plantations for biological control of chrysomelid leaf beetles

Abstract 1 Inundative augmentative releases of adult coccinellid beetles were assessed for their potential to effectively supplement biological control of outbreak populations of the Eucalyptus leaf beetle Chrysophtharta bimaculata in Eucalyptus nitens plantations. 2 Mixed groups of two species of overwintering coccinellids, Cleobora mellyi and Harmonia conformis, were collected from the field then fed three diets in the laboratory prior to release. Both species were released in the summer into two E. nitens plantations with economically damaging Chrysophtharta populations. 3 Differences between dispersal of coccinellids fed the three diets were slight; beetles brought straight out of overwintering before release were initially slower moving onto trees. 4 Numbers of coccinellids on trees in monitoring plots decreased exponentially with time, and populations had returned to prerelease levels 7 days after release. The number of coccinellids recaptured decreased with increasing distance from the release point with very few coccinellids per tree at 70 m distance. Dispersal of C. mellyi away from the release plot was slower than that of H. conformis. 5 Numbers of coccinellids on trees were significantly related to predation levels of C. bimaculata with a large decrease in the C. bimaculata population to below the economic damage threshold in plots where the numbers of coccinellids were high. 6 The results of this study suggest that inundative release of laboratory reared coccinellids is possible for biological control of C. bimaculata, although it may only be economically viable in small, environmentally sensitive areas.     

Sources of variability in the transition from extensive to intensive search in coccinellid predators (Homoptera: Coccinellidae)

In an environment structured by habitats, prey patches, and prey, predators such as coccinellids have two movement modes. The extensive search and the intensive search which results from prey capture are adopted for patch localization and exploration, respectively. The variability of changes from extensive search to intensive search was studied in larvae of the aphidophagous coccinellidSemiadalia undecimpunctata to find out their possibility of adaptation to a fluctuating environment. The temporal organization of coccinellid movements appears far more complicated than the generally accepted succession of extensive search, feeding, and intensive search. Their paths are characterized by the presence of time intervals devoted to intensive search before feeding, a highly variable path response after prey consumption (larvae may adopt intensive search immediately, later, or never), and the alternation of time periods devoted to either extensive search or intensive search after prey ingestion. This interindividual variability suggests that coccinellids have the ability to adapt to heterogeneity or short-term changes in environmental conditions, particularly in prey distribution. These results are in favor of the use of these predators in biological control programs.     

Instar-specific defense ofColeomegilla maculata lengi (Col.: Coccinellidae): Influence on attack success of the intraguild predatorChrysoperla rufilabris (Neur.: Chrysopidae)

We conducted a laboratory study of the behavioural interactions between larval stages of the lady beetleColeomegilla maculata lengi Timberlake and an intraguild predator, the lacewingChrysoperla rufilabris Burmeister. Ladybird susceptibility to predation by third instarC. rufilabris is age-specific and influenced by larval defensive strategies. First and second instars ofC. maculata were captured more consistently by chrysopid larvae than third and fourth instars. Young coccinellids generally exhibit escape reactions (dropping, fleeing, retreating) but, do not survive after being caught by lacewings. In addition to escape reactions, older larvae may actively defend themselves by wriggling or biting, even after being pierced. The proportion of physical interactions that resulted in coccinellid death was significantly lower for older instars (<2%) than for first (35%) and second (19%) instars. Capture efficiency byC. rufilabris was related to the coccinellid-chrysopid size ratio. Dropping off the leaves, the most common defensive behaviour displayed by coccinellid larvae, contributed to reduce overall mortality of first instars to a level similar to the one observed for older stages. However, lacewings were able to prevent coccinellid dropping by impaling and holding their prey in the air, or by falling with the ladybirds to the ground where they continued their attack.     

Food consumption and utilisation by larvae of two coccinellid predators, Scymnus levaillanti and Cycloneda sanguinea, on cotton aphid, Aphis gossypii

This study was carried out under laboratory conditions at various temperatures to compare food consumption and efficiency of conversion of food to body mass for larvae of two coccinellid predators, Scymnus levaillanti Mulsant (Coleoptera: Coccinellidae) and Cycloneda sanguinea (L.) (Coleoptera: Coccinellidae), which differ in body size and feeding method. The consumption rate of each larval stage of both species increased with increasing temperature. The consumption rate for total development (from egg hatch to pupation) of S. levaillanti was found to be 22.9 aphids per day at 30°C. It was much higher for C. sanguinea (975.1 aphids per day at 25°C and 1066 aphids per day at 30°C). The larger species, C. sanguinea was more voracious at each temperature than the smaller species, S. levaillanti. The larvae of S. levaillanti, employing pre-oral digestion, were more efficient in converting food to body mass than larvae of C. sanguinea, which used chewing and sucking. The fourth instars of both species were less efficient in converting food to body mass than were their first three instars. It was concluded that body size and feeding method of coccinellid predators play an important role in food consumption and efficiency of conversion of food to body mass.     

Status and importance ofRhyzobius forestieri (Col.: Coccinellidae) on citrus at chios Island, Greece, nine years after its introduction

The originally Australian coccidophagous predatorRhyzobius forestieri (Coleoptera: Coccinellidae), imported from California into Greece in 1981, was first released on citrus at Cambos, Chios, in 1983 against soft scalesCoccus pseudomagnoliarum andSaissetia oleae (Homoptera: Coccidae). It was successfully established in two orchards there. During the following decade,R. forestieri spontaneously dispersed throughout the Cambos coastal plain. In July 1992, a survey of coccidophagous coccinellids was carried out, to follow up on the dispersal ofR. forestieri on citrus and to compare its population size with that of the main native coccidophagous coccinellids. The samplings were made in 4 selected scale-infested orchards of Cambos spaced 1–2 km apart. Of a total of 337 adults and 237 larvae of coccidophagous coccinellids found,R. forestieri comprised 84.0% and 75.1%, respectively. It was present in all 4 localities; in 2,R. forestieri adults and larvae were by far the most abundant coccidophagous coccinellids.     

Effect of some plant extracts on two coccinellid predators of the cowpea aphid,Aphis craccivora (Hom.: Aphididae)

This study was conducted to examine the effects of some aphicidal biologically active plant compounds on the natural enemies of the cowpea aphid,Aphis craccivora Koch. In the laboratory, acetone extracts ofCymbopogon citratus (DC) Stapf.,Momordica charantia L.,Zingiber officinale Rose andAframomum melegueta (Rose) K. Schum, were tested for toxicity to two coccinellid species,Cheilomenes lunata (Fabricius) andCheilomenes vicina (Mulsant) predaceous on the aphid. All the extracts were highly ovicidal to eggs of the two coccinellid predators. None of the extracts caused mortality of eitherC. lunata orC. vicina fourth-instar larvae after 24 h. Larvae treated with the extracts consumed fewer aphids in 24 h than untreated larvae. Ability to pupate was also significantly reduced in larvae treated with the extracts. No morphological deformities were observed in adults emerging from treated larvae.     

Functional Response ofColeomegilla maculata(Coleoptera: Coccinellidae) to Colorado Potato Beetle Eggs (Coleoptera: Chrysomelidae)

A comparative study of the functional response ofColeomegilla maculataDeGeer (Coleoptera: Coccinellidae) fourth instars was conducted under laboratory, greenhouse, and field conditions. In the laboratory, individual larvae were placed in 9-cm petri dishes for 24 h, with 1, 3, 5, or 7 Colorado potato beetle (Leptinotarsa decemlineata[Say]) (Coleoptera: Chrysomelidae) egg masses. Each egg mass was standardized at 15 eggs. In the greenhouse and field,C. maculatalarvae were provided with an equivalent of 0.5 to 35L. decemlineataegg masses/m²of potato leaf. Fourth instars ofC. maculataexhibited a type II functional response toL. decemlineataeggs under laboratory, greenhouse, and field conditions. Predator search efficiency was inversely related with prey density. The maximum mean attack rate (8.7 eggs) byC. maculatalarvae in the field was about half the mean attack rate in the laboratory (17.6 eggs) and greenhouse (20.1 eggs). The difference in prey density between the laboratory and field seems to have been a major contributing factor in determining the rate of predation, whereas differences in environmental conditions (e.g., temperature and possible alternate food) may explain the differences observed in the predation rate in the greenhouse and field.     

Intraguild predation and native lady beetle decline

Coccinellid communities across North America have experienced significant changes in recent decades, with declines in several native species reported. One potential mechanism for these declines is interference competition via intraguild predation; specifically, increased predation of native coccinellid eggs and larvae following the introduction of exotic coccinellids. Our previous studies have shown that agricultural fields in Michigan support a higher diversity and abundance of exotic coccinellids than similar fields in Iowa, and that the landscape surrounding agricultural fields across the north central U.S. influences the abundance and activity of coccinellid species. The goal of this study was to quantify the amount of egg predation experienced by a native coccinellid within Michigan and Iowa soybean fields and explore the influence of local and large-scale landscape structure. Using the native lady beetle Coleomegilla maculata as a model, we found that sentinel egg masses were subject to intense predation within both Michigan and Iowa soybean fields, with 60.7% of egg masses attacked and 43.0% of available eggs consumed within 48 h. In Michigan, the exotic coccinellids Coccinella septempunctata and Harmonia axyridis were the most abundant predators found in soybean fields whereas in Iowa, native species including C. maculata, Hippodamia parenthesis and the soft-winged flower beetle Collops nigriceps dominated the predator community. Predator abundance was greater in soybean fields within diverse landscapes, yet variation in predator numbers did not influence the intensity of egg predation observed. In contrast, the strongest predictor of native coccinellid egg predation was the composition of edge habitats bordering specific fields. Field sites surrounded by semi-natural habitats including forests, restored prairies, old fields, and pasturelands experienced greater egg predation than fields surrounded by other croplands. This study shows that intraguild predation by both native and exotic predators may contribute to native coccinellid decline, and that landscape structure interacts with local predator communities to shape the specific outcomes of predator-predator interactions.     

Effects of augmentative releases of the coccinellid, Adalia bipunctata, and of insecticide treatments in autumn on the spring population of aphids of the genus Dysaphis in apple orchards

The impact of augmentative releases of indigenous predators and insecticide applications to control the autumn aphid forms of the genus Dysaphis (Homoptera: Aphididae), major pest insects on apple trees, was assessed in one-year field experiments in Switzerland. Eggs and larvae of the two-spot ladybird beetle Adalia bipunctata (L.) (Coleoptera: Coccinellidae) were released on 4-year old apple trees in various numbers at five different dates in autumn 1998 when sexuales of the aphids were present. Additionally, Pyrethrum HP was sprayed at the same five dates to compare the effectiveness of these augmentative releases to a commonly applied insecticide. Augmentative releases of larvae before mid-October significantly prevented the deposition of overwintering eggs by aphids of the genus Dysaphis and consequently reduced the number of hatched fundatrices in spring, 1999. There was a significant negative functional response among the number of released coccinellid larvae in autumn 1998 and the number of observed fundatrices on apple trees in spring 1999. Applications of Pyrethrum HP before mid-October were more effective than augmentative releases of larvae of A. bipunctata. The release of coccinellid eggs had no impact on the number of fundatrices of the genus Dysaphis in the next spring because they did not hatch due to bad weather conditions. The weather conditions in autumn seemed to have an impact on the autumn migration of the winged aphids back to their primary host. The prevention of egg deposition of aphids in autumn is a promising control strategy and deserves further exploration for practical use.     

The establishment ofRhyzobius forestieri [Col.: Coccinellidae] in greece and its efficiency as an auxiliary control agent against a heavy infestation ofSaissetia oleae [Hom.: Coccidae]

Introduction releases of the exotic coccinellid predatorRhyzobius forestieri Mulsant were made in 22 localities throughout Greece. The releases were made on olive, citrus, fig and almond trees infested with differentCoccidae scales. In 9 of these localities,R. forestieri was recovered 2–5 months later. The most important factor for the successful establishment ofR. forestieri seems to be an abundance of scales on the trees. To study the ability ofR. forestieri to enhance overall predation, 3 releases were made in an olive grove heavily infested withSaissetia oleae Olivier on Chios island during 1982 and 1983. The experiment began in June 1982. By April 1983, theS. oleae infestation was clearly in the process of being controlled by the coccinellid. A native coccinellid,Exochomus quadripustulatus L., contributed little during this period because of its obligatory estival diapause. The other main coccinellid,Chilocorus bipustulatus L., made an appreciable contribution toward achieving control during the summers of 1982 and 1983, but it was affected from July onward by increasing parasitism of its larvae. Both species are quiescent during the winter months. The introduced speciesR. forestieri was readily established in the olive grove and multiplied quickly. One month after the initial release,R. forestieri larvae made up most of the coccinellid larval population in the field. Thereafter until April 1983,R. forestieri larvae and adults comprised the dominant coccinellid population in the olive grove. During the winter months,R. forestieri remains active as long as temperature exceeds 8 °C. The important increase inR. forestieri's population size between July 1982 and April 1983 coincided with the increased rate of predation onS. oleae. This suggests thatS. forestieri played a key role in bringing theS. oleae infestation under control during this period. After April 1983, however, theR. forestieri population diminished rapidly andC. bipustulatus became the dominant coccinellid in the olive grove. It is believed that scarcity of prey was the cause of this reversal: by April 1983, the density ofS. oleae in the olive grove had already been reduced by about 100 times.     

Larval feeding on Bt hybrid and non-Bt corn seedlings by Harmonia axyridis (Coleoptera: Coccinellidae) and Coleomegilla maculata (Coleoptera: Coccinellidae)

Zoophytophagy is an omnivorous activity that occurs when a primarily carnivorous species feeds on plant material. Plant feeding by beneficial predators may have negative consequences if the plant material has been chemically treated, contains toxins, or was transgenically altered. Although common in predaceous Hemiptera, zoophytophagy has been rarely studied in aphidophagous coccinellids. This study examined the likelihood of feeding on Bt and non-Bt corn seedlings by third- and fourth-instar coccinellid larvae, the regularity of feeding events by fourth instars, and the effect of leaf feeding on development time and adult size. Both third- and fourth-instar Harmonia axyridis Pallas and Coleomegilla maculata DeGeer consume leaf tissue, with fourth instars being significantly more likely to feed on corn seedlings. C. maculata larvae ingested leaf tissue more frequently than H. axyridis. Furthermore, when given access to corn seedlings daily, development time of fourth-instar C. maculata increased after Bt hybrid corn treatments compared with non-Bt corn treatments. Zoophytophagous feeding behavior is thought to sustain predators during times of low prey availability, and leaf tissue feeding by coccinellids has typically been attributed to their need for water. However, in this study, tissue feeding regularly occurred even though coccinellid larvae had constant access to water and a daily ad libitum supply of aphids. We suggest that, in addition to environmental conditions, the physiological state of the zoophytophagous species will influence the probability of plant feeding.     

Suitability of exotic and native lady beetle eggs (Coleoptera: Coccinellidae) for development of lady beetle larvae

Predation upon lady beetle (Coleoptera: Coccinellidae) eggs in the field is most often instances of egg cannibalism by larvae or adults while the majority of the remaining predation events upon coccinellid eggs is done by other species of Coccinellidae. Thus the recent introduction and establishment of Harmonia axyridis in the US could negatively affect native species of Coccinellidae via egg predation. However, little is known regarding the suitability of interspecific coccinellid eggs as a food source for larval development. In this study, it was found that native first or third instar Coleomegilla maculata and Olla v-nigrum larvae were incapable of surviving to the adult stage when provided solely exotic H. axyridis eggs. In stark contrast, H. axyridis larvae survived equally well when cannibalizing eggs or eating eggs of either native species. When C. maculata and O. v-nigrum were grouped as ‘native’ and compared with the exotic H. axyridis, more native eggs were attacked than exotic eggs and a higher percentage of eggs was attacked by H. axyridis larvae. Native and exotic larvae attacked a similar percentage of native eggs but native larvae attacked significantly fewer exotic eggs than did exotic larvae. These data suggest that H. axyridis may prey upon the eggs of these native species, when encountered in the field, compared with the likelihood of the native species preying upon H. axyridis eggs. Therefore, eggs of the native species C. maculata and O. v-nigrum will continue to be subjected to cannibalism and also to possible predation by other native species and the exotic H. axyridis.     

Coccinellid immigration to infested host patches influences suppression of Aphis glycines in soybean

Generalist natural enemies may be well adapted to annual crop systems in which pests and natural enemies re-colonize fields each year. In addition, for patchily-distributed pests, a natural enemy must disperse within a crop field to arrive at infested host patches. As they typically have longer generation times than their prey, theory suggests that generalist natural enemies need high immigration rates to and within fields to effectively suppress pest populations. The soybean aphid, Aphis glycines Matsumura, is a pest of an annual crop and is predominantly controlled by coccinellids. To test if rates of coccinellid arrival at aphid-infested patches are crucial for soybean aphid control, we experimentally varied coccinellid immigration to 1 m² soybean patches using selective barriers and measured effects on A. glycines populations. In a year with low ambient aphid pressure, naturally-occurring levels of coccinellid immigration to host patches were sufficient to suppress aphid populations, while decreasing coccinellid immigration rates resulted in large increases in soybean aphid populations within infested patches. Activity of other predators was low in this year, suggesting that most of the differences in aphid population growth were due to changes in coccinellid immigration. Alternatively, in a year in which alate aphids continually colonized plots, aphid suppression was incomplete and increased activity of other predatory taxa contributed to adult coccinellid predation of A. glycines. Our results suggest that in a system in which natural enemy populations cannot track pest populations through reproduction, immigration of natural enemies to infested patches can compensate and result in pest control.     

The effect of aphid prey quality on searching behaviour of Adalia bipunctata and its susceptibility to insecticides

After consumption of one individual of a suitable prey, such as Phorodon humuli (Schrank) (Aphididae), Adalia bipunctata L. (Coleoptera, Coccinellidae) adults changed from extensive to intensive searching behaviour. However, after the consumption of one individual of three other aphid species: Aphis fabae Scop., Aphis craccivora Koch or Aphis spiraephaga Müller, which are unsuitable prey, this coccinellid remained immobile for 12–76 min and did not switch to intensive search after moving off. Adult A. bipunctata fed an unsuitable prey, A. fabae, for 2 weeks were 2–4 times more susceptible to pyrethroid insecticides (permethrin, deltamethrin, fenpropathrin, esfenvalerate, alfa-cypermethrin and bioresmethrin) and insect growth regulators (diflubenzuron, triflumuron, fenoxycarb, flufenoxuron, teflubenzuron) than those fed a suitable prey, P. humuli.The searching behaviour of coccinellids could thus be another criterion for determining the suitability of aphids as prey. The fact that the nutritional quality of aphids can affect the susceptibility of predatory coccinellids to insecticides should be borne in mind in integrated pest management programs.     

Intra-tree foraging behavior ofDacus dorsalis flies in relation to host fruit quantity, quality and type

Promising diets were screened and the most successful modified with additives used in artificial diets for other entomophagous insects. Two suitable diets were obtained, one for adults and one for larvae ofChilocorus nigritus (Fabricius) (Coleoptera: Coccinellidae). They were still inferior to natural prey and not adequate as the sole food source for rearing consecutive generations. They are valuable as substitute food in the insectary during shortages of natural prey. Oleander scaleAspidiotus nerii Bouché andAsterolecanium miliaris (Boisduval) were evaluated as natural prey forC. nigritus and two other potential biocontrol agents in southern Africa,C. bipustulatus (Linnaeus) andC. infernalis Mulsant.A. nerii andA. miliaris were suitable for all life stages ofC. nigritus and adults ofC. bipustulatus andC. infernalis. A. miliaris was inadequate for larvae ofC. bipustulatus andC. infernalis.     

Learning affects prey selection in larvae of a generalist coccinellid predator

Under natural conditions, generalist predatory insects have to cope with a variety of potential prey species that are not all equally suitable. Under these circumstances, learning may be adaptive if it allows adjustment to variations in resource quality and availability. Under laboratory conditions, we examined the learning ability and memory in the prey selection process of larvae of the predatory coccinellid Coleomegilla maculata ssp. lengi Timberlake (Coleoptera: Coccinellidae). Using choice tests, we studied prey rejection behaviour of C. maculata fourth instars towards prey of different quality and we also tested the influence of hunger and prior experience with other food types on the prey rejection behaviour of coccinellid larvae. Coleomegilla maculata larvae gradually changed their behaviour and rejected low‐quality hosts more frequently, whereas high‐quality hosts were nearly always accepted. After 48 h, the learned behaviour appeared to be partially forgotten. Hunger and experience with other food types prior to the test had little effect on the gradual change of behaviour but the quality of the food ingested influenced the initial level of prey rejection. Our results demonstrate that (1) C. maculata larvae can adjust their prey selection behaviour with experience to reject progressively less suitable prey, and (2) previous experience with other prey types can influence their initial preference.     

How the aphids got their spots: predation drives self‐organization of aphid colonies in a patchy habitat

Using a 30 day time series of aphid Aphis helianthi and coccinellid counts on 107 mapped racemes of Yucca glauca, we demonstrate progressive, predation‐induced self‐organization of aphid colonies on individual racemes into extremely low and extremely high population sizes. This was driven by a two‐attractor structure of density dependence that developed only in the presence of coccinellid predators. Foraging movements of the coccinellids among plants produced a power law relationship (average power = 0.142) between aphid and coccinellid numbers. This resulted in increased predation pressure on mid‐size colonies and decreased predation pressure on small and large populations. A field‐parameterized mathematical model predicts a two‐attractor structure in broad agreement with our observations. The overall system was integrated by the influence of the largest aphid populations, which determined the total number of coccinellids present, and thus the predation pressure throughout the system. Our study provides clear evidence of predator‐driven self‐organization of prey populations in a patchy environment.     

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.