Feeding history affects intraguild interactions between Harmonia axyridis (Coleoptera: Coccinellidae) and Episyrphus balteatus (Diptera: Syrphidae)

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

Effect of size, extraguild prey and habitat complexity on intraguild interactions: a case study with the invasive ladybird Harmonia axyridis and the hoverfly Episyrphus balteatus

Intraguild predation (IGP) is a widespread interaction between predatory arthropods, and is influenced by several factors. The harlequin ladybird, Harmonia axyridis (Coleoptera: Coccinellidae), has frequently been reported as an intraguild predator of other Coccinellidae, but little is known about its interactions with other aphidophagous predators, including syrphids. This study investigated the incidence of IGP between H. axyridis and Episyrphus balteatus (Diptera: Syrphidae), the most abundant hoverfly species in Europe and a commercially available aphid biocontrol agent. The influence of size, presence of extraguild prey and habitat complexity were investigated through laboratory experiments in Petri dishes and on potted broad bean plants. In both types of arenas, IGP between H. axyridis and E. balteatus was found to be asymmetric, with the coccinellid in the majority of cases being the intraguild predator. There was a significant effect of size on the frequency of IGP. The efficiency of H. axyridis as an intraguild predator increased with the developmental stage. Early instars of E. balteatus were the most vulnerable to IGP. Pupae of either species were not attacked. In the presence of extraguild prey, the frequency of IGP was substantially reduced. However, IGP still occurred, mainly in combinations of older larvae of H. axyridis with first or second instars of E. balteatus. The size of the arena affected the incidence of IGP in combinations with second instars of E. balteatus, but not in combinations with third instars. Field research is needed to elucidate the ecological relevance of IGP among these predators

Intraguild predation between Harmonia axyridis and the hoverfly Episyrphus balteatus

Whereas Harmonia axyridis has frequently been reported as an intraguild predator of other Coccinellidae, little is known about its interactions with other aphidophagous predators, including syrphids. This study investigated the incidence, direction and magnitude of intraguild predation (IGP) between H. axyridis and Episyrphus balteatus in Petri dish arenas with leaf disks on agar. The interactions were examined between larvae, pupae and adults, both in the absence and presence of Acyrthosiphon pisum as an extraguild prey. IGP between H. axyridis and E. balteatus was asymmetric, with the coccinellid in the majority of cases being the IG predator and the syrphid the IG prey. In the absence of extraguild prey, first instars of E. balteatus were most sensitive to IGP, as they were killed by all stages of H. axyridis. Second and third instars of the syrphid were only killed by older larvae and adults of the coccinellid. Pupae of either species were not attacked. In the presence of extraguild prey, the frequency of IGP was substantially reduced. Further research using larger arenas is needed to get a more reliable view on the interactions between these predators

Molecular analysis of the gut contents of Harmonia axyridis (Coleoptera: Coccinellidae) as a method for detecting intra-guild predation by this species on aphidophagous predators other than coccinellids

Several studies have demonstrated that the invasive ladybird Harmonia axyridis is a strong intra-guild predator of native species of ladybird. Laboratory studies have shown that H. axyridis can be an intra-guild predator of aphid predators other than coccinellids, including the hoverfly Episyrphus balteatus and lacewing Chrysoperla carnea. However, little is known about the effect of intra-guild predation (IGP) by H. axyridis on hoverfly and lacewing populations in the field. In the present study molecular analyses were used to detect the DNA of E. balteatus and C. carnea in the gut contents of H. axyridis. Primers for the syrphid and chrysopid prey were designed and feeding experiments performed to determine how long prey DNA remains detectable in the guts of this ladybird. DNA detection was influenced by the life stage of the predator and species of prey. Meal size did not affect detection time, except when fourth instar individuals of H. axyridis were fed 10 eggs or one second instar of C. carnea. Predator weight, sex and morpho-type (melanic/non-melanic) did not influence DNA detection. The half-life of the time for which the DNA of the prey remained detectable was calculated for each predator-prey combination, and ranged from 8.9 to 52.4 h. This method can be used to study the ecological importance of IGP by H. axyridis on aphidophagous predators other than coccinellids in the field

Total developmental time of <i>Episyrphus balteatus</i> immatures (from first instar to adulthood), weight of the third instar, survival time under starvation of third instars and 6h predation rate by third instars (% of <i>Acyrthosiphon pisum</i> aphids killed) when offered various diets.

<p>Values in the same column followed by a different letter are significantly different. n: sample size.</p><p>Total developmental time of <i>Episyrphus balteatus</i> immatures (from first instar to adulthood), weight of the third instar, survival time under starvation of third instars and 6h predation rate by third instars (% of <i>Acyrthosiphon pisum</i> aphids killed) when offered various diets.</p

Total developmental time of <i>Harmonia axyridis</i> immatures (from first instar to adulthood), weight of the fourth instar, survival time under starvation of third instars and 6h predation rate by third instars (% of <i>Acyrthosiphon pisum</i> aphids killed) when offered various diets.

<p>Values in the same column followed by a different letter are significantly different. n: sample size.</p><p>Total developmental time of <i>Harmonia axyridis</i> immatures (from first instar to adulthood), weight of the fourth instar, survival time under starvation of third instars and 6h predation rate by third instars (% of <i>Acyrthosiphon pisum</i> aphids killed) when offered various diets.</p

IGP by <i>Harmonia axyridis</i> on <i>Episyrphus balteatus</i> on potted pepper plants after 24h.

<p>Percentage of third instars of <i>Episyrphus balteatus</i> reared on an <i>ad libitum</i> or limited supply of aphids that were killed through IGP on pepper plants after 24h by third instars of <i>Harmonia axyridis</i> reared on various diets. Aph ad lib: <i>ad libitum</i> supply of <i>Acyrthosiphon pisum</i> aphids, Aph lim: limited supply of aphids, Pollen: moist honey bee pollen. No statistically significant effect of larval diet of <i>H</i>. <i>axyridis</i> was found (generalized linear model with Poisson error distribution and a log link function). Error bars represent SE-values.</p