Impact of poor host-parasitoid synchronisation on the parasitism of Cameraria ohridella (Lepidoptera: Gracillariidae)

Abstract

Abstract. Poor synchronisation is considered to be one important reason for the ineffective control of the invasive horse chestnut leafminer by native parasitic Hymenoptera. Parasitoids hibernating in dry horse chestnut leaves break diapause early in spring and presumably leave the vicinity, since no hosts are available when they emerge. As a consequence, the percentage parasitism of the first generation of the leafminer in early summer is low. The experiments presented below were designed to test this hypothesis. Horse chestnut saplings were brought on in a greenhouse and infested artificially with C. ohridella prior to parasitoid emergence in the field. These saplings were then exposed to parasitoid attack under natural conditions to eliminate the synchronisation problem. In addition, the parasitoid complexes of other leafmining hosts, which appear early in the season, were analysed. The results confirm that the most important parasitoids of the horse chestnut leafminer are active early in the season, long before the larvae of the first generation of the host are present. Nevertheless, poor synchronisation with the invasive host did not significantly influence the abundance of the most important parasitoid in the complex, Minotetrastichus frontalis, and consequently had no impact on the parasitism of C. ohridella. Nevertheless, a detailed analysis of the parasitoid community shows that certain species are affected by poor synchronisation, while others are probably limited by ecological parameters, such as a specialisation to foraging in particular strata of vegetation. Several leafmining flies were found early in spring infesting other host plants commonly planted in urban green areas, including species with a parasitoid complex similar to that of C. ohridella. The role of these alternative hosts in the food web associated with the horse chestnut leafminer should be subject to further study.

Spatial variability in the level of infestation of the leaves of horse chestnut by the horse chestnut leaf miner, Cameraria ohridella (Lepidoptera: Gracillariidae) and in the number of adult moths and parasitoids emerging from leaf litter in an urban environment

“…There was a two-week delay in peak moth emergence in 2014 compared to 2013, which was most likely due to differences in temperature during winter and early spring. The results also revealed that parasitoids started to emerge from fallen leaves earlier than horse chestnut leaf-miner, which is well documented by many authors (Hellrigl, 2003;Grabenweger, 2004;Grabenweger et al, 2007). Poor synchronization between parasitoid emergence and C. ohridella development is believed to be the reason for the lack of control of this species in the fi rst generation (Grabenweger, 2004), but does not signifi cantly affect the abundance of the most important parasitoid in the complex, Minotetrastichus frontalis, and consequently has no effect on the parasitism of C. ohridella (Grabenweger et al, 2007).…”

“…Its parasitoid complex (Hymenoptera) includes about 20 species. The most dominant species are Minotetrastichus frontalis (Nees) and Pediobius saulius (Walker) (Hymenoptera: Eulophidae) (Volter & Kenis, 2006;Grabenweger et al, 2007;Cebeci et al, 2011). These two species are also the most abundant parasitoids recorded in the Czech Republic (Zemek et al, 2006).…”

“…Parasitoids do not attack eggs and fi rst instar larvae of C. ohridella but usually prefer attacking the 4 th -6 th larval instars (Grabenweger, 2003). In spring the parasitoids are poorly synchronized with C. ohridella and as a consequence do not regulate the abundance of this pest (Grabenweger, 2004;Grabenweger et al, 2007). The mortality of fi rst generation of the horse chestnut leaf miner is very low compared to that of other taxonomically closely related mining moths (Zemek et al, 2006;Grabenweger, 2003).…”

The horse chestnut leafminer Cameraria ohridella: chemical control and notes on parasitisation

“…Although the observed diversity of the parasitoid complex was quite low, we consider our Moreth et al 2000;Balász et al 2002;Grabenweger 2002;Lethmayer 2002;Grabenweger et al 2005Grabenweger et al , 2007Lupi 2005;Volter & Kenis 2006). The spectrum of parasitoid species corresponds with previously published data except for one undetermined species of mymarid, which was recorded for the first time from horse chestnut leaves infested by larvae of C. ohridella.…”

Natural prevalence of entomopathogenic fungi in hibernating pupae of Cameraria ohridella (Lepidoptera: Gracillariidae) and virulence of selected isolates

“…Backhaus et al 2002;Grabenweger 2003;Grabenweger et al 2005aGrabenweger et al , b, 2007Rämert et al 2011). Control measures of the leaf miner populations focus mostly upon mechanical (Gilbert et al 2003;Kehrli & Bacher 2003;Pavan et al 2003) and chemical control (Kuldová et al 2007), however their effectiveness is either short-term or ecologically questionable.…”