ABSTRACT
A long-term monitoring was conducted at 40 sites in four different habitats in north-western Switzerland to observe changes in populations of native ladybirds, following the invasion of the Asian harlequin ladybird, Harmonia axyridis. From 2006 to 2017, the same trees and meadows were sampled at least seven times per year using standard protocols. On 15 broadleaved hedges, H. axyridis quickly became the dominant species, representing 60 to 80% of adult ladybirds collected. It was second in abundance at five pine (Pinus sylvestris) stands and was a minor component of the ladybird complex at five spruce (Picea abies) stands and in 15 meadows. This survey revealed the severe decline of Adalia bipunctata, which was the most abundant native ladybird on broadleaved trees in 2006-2009 and has almost disappeared since 2010. So far, other native ladybirds do not seem to decline significantly, including species occupying the same ecological niches as H. axyridis. The total number of aphidophagous ladybirds did not decline either, suggesting that the biological control function of ladybirds on aphids living in these habitats has not been affected by the arrival of H. axyridis. Recommendations are given to further assess the impact of H. axyridis on native ladybirds and aphids.
ABSTRACT
Sociality is associated with many benefits that have favoured its evolution in social insects. However, sociability also presents disadvantages like crowding of large numbers of individuals, which may favour the spread of infections within colonies. Adaptations allowing social insects to prevent and/or control pathogen infections range from behavioural responses to physiological ones including their immune systems. In a state of infection, social interactions with nestmates should be altered in a way which might prevent its spreading. We simulated a microbial infection in workers of the ant Camponotus fellah by the administration of peptidoglycan (PGN) and then quantified their immune response and social interactions. PGN injections as well as control injections of Ringer solution elicited similar production of antibacterial compounds, during 1-4 days after. However, injections of PGN reduced the ability of encapsulation of a nylon implant compared to Ringer controls. The immune challenged workers did not decrease the level of interactions with their nestmates. On the contrary, they devoted more time to trophallaxis. These results are discussed in relation to ant life history traits.
