Estimation of mortality by entomophages on exotic Harmonia axyridis versus native Adalia bipunctata in semi-field conditions in northern Italy

Abstract

A semi-field experiment was carried out in two peach orchards in northern Italy to assess mortality due to predators and parasitoids on the exotic coccinellid Harmonia axyridis (Pallas) (Coleoptera: Coccinellidae) in comparison with the native coccinellid Adalia bipunctata L. (Coleoptera: Coccinellidae). The experiments were conducted in cages to avoid the possible escape of the exotic ladybird (not yet established in Italy). Two kinds of cage experiments were included: 'exclusion cages' (access by walking predators impeded) and 'free cages' (walking predators free to enter). The cages, containing all the stages of the two ladybird species, were placed in two localities and left for 24 h. All ladybird stages used for the semi-field experiments came from a laboratory rearing. The eggs of H. axyridis experienced less mortality than those of A. bipunctata. The ant workers were the most frequent predators in 'free cages' but A. bipunctata cannibalism on eggs was also detected. Larvae of both coccinellid species were predated equally but larval predation of L1 and L2 was higher in comparison to predation of L3 and L4. Pupae and adults of both exotic and native ladybirds were never attacked by predators. Predation on younger larval stages was higher in the 'free cages' in comparison with 'exclusion cages'. No ladybird parasitisation was observed. The 'free cage' technique seems to provide a standardised and realistic estimation of predation impact but more studies are needed to evaluate ladybird parasitisation in semi-field conditions.

Predators and parasitoids of the harlequin ladybird, Harmonia axyridis, in its native range and invaded areas

“…Most frequently only qualitative assessment of the diet of predators has been determined, either through direct observation of predation events or identification of prey remnants in predator's alimentary tract or faeces (Harwood and Obrycki 2005;Michalski et al 2011). An attempt to quantify the effect of invertebrate predators on H. axyridis and the two-spot ladybird, Adalia bipunctata (L.), was made in northern Italy by Burgio et al (2008). Using outdoor cage experiments, they found that the rate of predation on H. axyridis eggs did not exceed 2%, while up to 40% of the eggs of A. bipunctata were consumed or destroyed.…”

“…Individual larval instars, however, were preyed on at similar rates in both species. The cage method (sensu Burgio et al 2008) can provide some estimation of the overall predation but it cannot indicate with certainty which predators are involved. The effectiveness and prey preference of individual predators are often assessed in laboratory experiments, and this also applies to predation on ladybirds, including H. axyridis (HoughGoldstein et al 1996;Yasuda and Kimura 2001;De Clercq et al 2003;Santi and Maini 2006;Sloggett 2010a;Průchová et al 2014;Veselý et al 2016).…”

Exotic Insects in Italy: An Overview on Their Environmental Impact

“…Many studies have documented invaders that show a superior ability to exploit local resources as compared with native residents (Bazzocchi et al, 2004;Burgio et al, 2008;Holway, 1998) or as compared with non-invading introduced species. The Argentine ant (Linepithema humile) is not only an agricultural and house pest but is also competitively superior to the native ant species in both interference and exploitative competition in the riparian woodlands of northern California and in the alteration of plant community structure (Holway, 1998;Suarez et al, 2008).…”

Laboratory studies on intraguild predation and cannibalism among coccinellid larvae (Coleoptera: Coccinellidae)

“…The exotic coccinellid Harmonia axyridis (Pallas) (Coleoptera: Coccinellidae) was intentionally introduced into Northern Italy in the 1990s for the biological control of aphids and psyllids (Bazzocchi et al, 2004;Burgio et al, 2008). At present this species is established in several areas of Northern and Central Italy and is spreading (Burgio et al, 2008;Croci et al, 2010).…”

“…At present this species is established in several areas of Northern and Central Italy and is spreading (Burgio et al, 2008;Croci et al, 2010).…”