Susanne Harding

Living with the enemy: parasites and pathogens of the ladybird Harmonia axyridis

Harmonia axyridis is an invasive alien predator in many countries across the world. The rapid establishment and spread of this species is of concern because of the threat it poses to biodiversity as a generalist predator. Understanding the mechanisms that contribute to the success of this species as an invader is not only intriguing but also critical to our understanding of the processes governing such invasions. The enemy release hypothesis (ERH) could explain the rapid population growth of many invasive alien species. However, empirical evidence in support of the ERH is lacking. An alternative hypothesis that could explain rapid population growth is evolution of increased competitive ability (EICA). Here we provide an overview of the parasites and pathogens of coccinellids with a particular focus on H. axyridis as a host. We examine the differential susceptibility of host species and highlight the resilience of H. axyridis in comparison to other coccinellids. We recognise the paucity and limitations of available information and suggest that studies, within a life-table framework, comparing life history traits of H. axyridis in both the native and introduced ranges are necessary. We predict that H. axyridis could benefit from both enemy release and EICA within the introduced range but require further empirical evidence.

Entomopathogenic fungi recorded from the harlequin ladybird, Harmonia axyridis

Entomopathogenic fungi were recorded from field samples of the harlequin ladybird Harmonia axyridis, an invasive coccinellid that has recently arrived in Denmark. Larvae, pupae and adults were found to be infected by Isaria farinosa, Beauveria bassiana and species of Lecanicillium. This is the first record of entomopathogenic fungi infecting larvae and pupae. Winter mortality due to fungal infection reached 17.9% in adults collected at one location. The larval stage was most susceptible to fungal infection, as confirmed through bioassay with I. farinosa.

Biological control of Strophosoma spp. (Coleoptera: Curculionidae) in greenery (Abies procera) plantations using Hyphomycetes

Abstract In Abies procera plantations Strophosoma melanogrammum and S. capitatum cause economic damage due to the adult stage feeding on the needles. No chemical treatments of these weevils are allowed in Denmark, so the potential of biological control was evaluated. We studied pathogenicity of thirteen isolates of entomopathogenic fungi and the field effect of soil application of Metarhizium anisopliae against Strophosoma spp. All of the tested isolates were capable of causing infections under laboratory conditions and average survival time at 20°C ranged between 13 and 23 days for S. melanogrammum and between 23 and 28 days for S. capitatum when dipped in a fungal suspension adjusted to 1×107 conidia mL−1. Under field conditions up to 90% of the living collected individuals died due to M. anisopliae infection in the treated plots, whereas less than 1% died of M. anisopliae infection in control plots. In accordance, the population of Strophosoma spp. was reduced in plots where the fungus was applied compared to control plots.

Observations on the activity and development of Pityogenes chalcographus L. (Col., Scolytidae) in stands of Norway spruce in Denmark

Exploitation of thinnings in young stands of Norway spruce for the production of chips necessitates a period of seasoning of the felled trees in the stand. This infers a potential risk of bark beetle attack on standing trees. The seasonal activity and reproduction of Pityogenes chalcographus L. were studied in shade and half‐shade ‐ conditions representative of thinning by rows. In half‐shade chipping is required before August in order to avoid emergence of the offspring from trees infested during the early spring flight in May. From trees attacked later on or lying in shade emergence is delayed and chipping can be carried out until next spring.

BIOLOGICAL CONTROL OF SCARABS AND WEEVILS IN CHRISTMAS TREES AND GREENERY PLANTATIONS

In Danish forestry the economically most important insect problems and consequently the most intensive use of chemical insecticides occur in the production of Christmas trees and decoration green (Kirkeby-Thomsen and Ravn, 1997; Ravn, 2000). Nordmann fir (Abies nordmanniana) and noble fir (Abies procera) are the dominant tree species in this production today. Abies nordmanniana is mostly used for Christmas trees, while A. procera is mostly used for decoration green. Other conifer species to be used for the same purposes are only grown on a negligible scale. Christmas trees and decoration green are both important for the home market and export. In several countries in Central and Northern Europe with Germany as the main recipient. The prices obtained by the producers vary depending on quality, but can typically be around EUR 10 per tree of 200 cm height and EUR 1 per kg decoration greenery. The total export value for Denmark was thus above EUR 150 mio in 2003. The market demands a very high product quality, and no damage from feeding of insect pests is accepted. Only the highest quality with the required shiny, dark green needle colour of Christmas trees and decoration greenery without any signs of insect feeding on the needles are saleable at reasonable prices. It is therefore a prerequisite for the producers to ensure pest control. Control of insect pests in the Danish production of Christmas trees and decoration green has historically been based on the use of chemical pesticides. However no chemical pest control have been permitted in state forestry since 2003 (The Danish Environmental Protection decoration greenery. For privately owned forests there is a political wish from the state authorities to phase out chemical pesticides (Ravn, 2000). Further, there is an increasing desire from consumers to buy organically grown Christmas trees produced without chemical pesticides. The products are associated with strong emotions among consumers: Christmas trees and decoration green are linked to family traditions during the Christmas period, which in Denmark lasts about one month. Biological control using natural enemies of the pest populations may thus provide an attractive alternative to conventional chemical treatment. This chapter provides a short review