Responses of native egg parasitoids to the invasive seed bug Leptoglossus occidentalis

Abstract

The Western conifer seed bug Leptoglossus occidentalis, a native insect of North America, was accidentally introduced in Europe in the late 1990s. Since then, it has spread rapidly. Biological control could provide an efficient management option but natural enemies of the pest have been poorly examined in Europe. 2 In this study, we exposed sentinel egg masses and collected naturally laid egg masses in southern France in 2016 and 2017, to identify the egg parasitoids of L. occidentalis and investigate their potentials. 3 Three egg parasitoids were detected: Anastatus bifasciatus, Ooencyrtus pityocampae and Ooencyrtus telenomicida. The overall parasitism was low compared to that observed in the native range with 6.4% of all eggs being parasitized, while 17.1% of egg masses carried at least one parasitized egg. The total number of parasitized egg masses was similar between parasitoid species, but the mean number of parasitized eggs per egg mass was highest for A. bifasciatus (5.57 vs. 1.25 for Ooencyrtus spp.). 4 Sentinel egg masses underestimated the parasitism compared to natural egg masses (respectively, 1.42% and 7.71%). 5 Our results suggested that the three generalist parasitoids detected can respond in a Leptoglossus egg density-dependent manner, but this requires further investigations.

Native egg parasitoids on Leptoglossus occidentalis Heidemann (Hemiptera: Coreidae) in Spain: Potential biological control agents?

“…The amount of natural eggs parasitized in France by A. bifasciatus (176; parasitism rate : 4.8%) was lower than the values recorded in the 2017 clone bank and the 2019 pine forest trials, whereas the percentage of natural eggs parasitized by Ooencyrtus spp. (50; parasitism rate : 1.3%) was lower than those reported in our trials for Ooencyrtus for both species (Lesieur & Farinha, 2021).…”

“…In all trials, the number of WCSB egg masses and eggs varied weekly and depended on the number and fecundity of the bagged WCSB females in field. The unhatched eggs rate in the clone bank trials differs from that for sentinel egg masses recorded in France (8.4%-11.3%) (Lesieur & Farinha, 2021) and in British Columbia (2%-16%),…”

“…However, the first WCSB egg masses and parasitized eggs were found simultaneously. In France, no parasitized egg masses were recorded before July but were detected in a longer timeframe when compared to Spain (Lesieur & Farinha, 2021).…”

“…However, the first WCSB egg masses and parasitized eggs were found simultaneously. In France, no parasitized egg masses were recorded before July but were detected in a longer timeframe when compared to Spain (Lesieur & Farinha, 2021). To define the synchronization between the WCSB and the native egg parasitoids (Stiling, 1993), it is necessary to properly define the parasitoid activity period by surveying egg masses of their primary hosts, which could be more attractive for them, causing a decrease in impact on the WCSB population.…”

“…However, BCPs based on inundative or conservative methods (Eilenberg et al., 2001) could be proposed with the WCSB egg parasitoid community native to Europe, which is influenced by the environmental conditions, type of vegetation, main host populations and its densities (Costi et al., 2018). In Italy and France, different native parasitoid communities formed by the genera Anastatus , Baryscapus and Ooencyrtus have been associated with WCSB eggs (Lesieur & Farinha, 2021; Niccoli et al., 2009; Roversi et al., 2011). The aims of this study were (I) to survey and identify the native egg parasitoid community of the WCSB in Central Spain and (II) to estimate its impact on the WCSB population through four parasitism indexes.…”