Intraguild predation between the invasive ladybird Harmonia axyridis and non-target European coccinellid species

The coccinellid Harmonia axyridis (Pallas) has been used for augmentative and classical biological control in many environments. More recently it has invaded large parts of Europe and negative effects for native populations of aphidophagous coccinellids are beginning to emerge. Here we investigate intraguild predation (IGP) between H. axyridis and eleven native non-target European coccinellids, including less common species which have not been studied so far within this context of non-target effects. When first-instars of H. axyridis were paired with the native species, only Anatis ocellata (Linnaeus) and Calvia quatuordecimguttata (L.) were significantly superior to the former whereas H. axyridis was superior in three cases, i.e. against Aphidecta obliterata (L.), Coccinella septempunctata L. and Hippodamia variegata (Goeze). Non-significant results were obtained for all other pairings. Similar tests with the fourth larval instar revealed stronger IGP rates and H. axyridis was found to be superior in the interactions with Adalia bipunctata (L.), Adalia decempunctata (L.), A. obliterata, Calvia decemguttata (L.), C. quatuordecimguttata, C. septempunctata, H. variegata, Oenopia conglobata (L.) and Propylea quatuordecimpunctata (L.) whereas non-significant results were obtained for interactions with two other native species. Another experiment revealed that H. axyridis was able to prey more successfully upon egg of most native coccinellid species than vice versa. However, C. quatuordecimguttata eggs seem to be more protected against predation than those of the other species. Survival of first-instar H. axyridis was higher on conspecific eggs compared to eggs of any other species tested. Our results suggest that H. axyridis may become a threat to a wide range of native aphidophagous coccinellids sharing similar ecological niches except species showing high potential for chemical or physical protectio

Assessing the ecological risk posed by a recently established invasive alien predator: Harmonia axyridis as a case study

Invasive alien predators are a serious threat to biodiversity worldwide. However, there is no generic method for assessing which local species are most at risk following the invasion of a new predator. The harlequin ladybird, Harmonia axyridis (Pallas) (Coleoptera: Coccinellidae), is an alien in Europe and many other parts of the world where it affects other species of ladybirds through competition for food and intra-guild predation (IGP). Here, we describe a method developed to assess which European ladybird species are most at risk following the invasion of H. axyridis. The three components of the risk assessment are: the likelihood that the assessed native species encounters H. axyridis in the field, the hazard of competition for food, and the IGP hazard. Thirty native European ladybird species were assessed through data obtained from field observations, laboratory experiments and literature reviews. The species that are considered most at risk are found on deciduous trees, have immature stages which are highly vulnerable to IGP by H. axyridis, and are primarily aphidophagous. These species should be the focus of specific studies and possibly conservation actions. The risk assessment method proposed here could be applied to other alien predators which are considered a threat to native species through competition and predation

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

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

Glucosinolates (GLS) levels in A) leaves of two <i>Brassica napus</i> varieties following aphid herbivory.

<p>Means ± 1SE are shown for <i>Brassica napus</i> var. Dwarf Essex (DE) and var. Amanda (AM) after damage by <i>Brevicoryne brassicae</i> and <i>Myzus persicae</i> and for healthy (control) plants. Panel B) shown mean glucosinolate content in aphids’ bodies after feeding on both <i>B</i>. <i>napus</i> varieties. Letters above bars means significant differences (TukeyHSD test, p < 0.05).</p

Effect of host plant chemical defense on aphid resistance and coccinellid performance.

<p>The panels show means ± 1SE for A) voracity (number of aphids consumed during development to the 4^th instar; inverse of aphid resistance), B) the development time in days to the 4th instar, and C) weight gain from to the 4th instars separately for 5 coccinellid species and overall means across all 5 species. The following coccinellid species were used: <i>Anatis rathvoni</i> (<i>A</i>. <i>rat</i>); <i>Coccinella septempunctata</i> (<i>C</i>. <i>sep</i>.), <i>Cycloneda sanguinea</i> (<i>C</i>. <i>san</i>.), <i>Harmonia axyridis</i> (<i>H</i>. <i>axy</i>.) and <i>Hippodamia convergens</i> (<i>H</i>. <i>con</i>.). Values are provided for <i>Brevicoryne brassicae</i> (black and dark gray bars) and <i>Myzus persicae</i> (light gray and open bars) feeding on either a low or high glucosinolate variety of <i>Brassica napus</i> (var. Amanda (AM) and var. Dwarf Essex (DE)). Letters above bars means significant differences (TukeyHSD test, p < 0.05).</p

Total glucosinolate concentrations in plants and aphids.

<p>Total glucosinolate concentrations in plants and aphids.</p

Results of statistical tests for the effect of plant variety and aphid herbivory on glucosinolate production and sequestration.

<p>Results of statistical tests for the effect of plant variety and aphid herbivory on glucosinolate production and sequestration.</p