Mortality factors affecting Agrilus auroguttatus Schaeffer (Coleoptera: Buprestidae) eggs in the native and invaded ranges

Native and introduced range surveys for egg parasitoids ofAgrilus auroguttatus, an invasive pest of native oaks in California

“…Co-evolved, host-specific egg parasitoids of A. auroguttatus may not occur in the native range of this beetle. Although a generalist egg parasitoid, Trichogramma sp., was found to attack A. auroguttatus eggs at very low levels (approximately 0.1%) during surveys conducted in the Santa Rita Mountains, Arizona in 2012, no additional parasitoids were detected (Lopez & Hoddle, 2013). The absence of parasitism from >18,000 A. auroguttatus eggs deployed throughout infested sites in southern Arizona and California in 2013, and the rarity of parasitism recorded from >10,000 eggs deployed in similar treatments in Arizona and California in 2012 (Lopez & Hoddle, 2013) suggests that host-specific egg parasitoids of this beetle may not exist within the areas sampled, and parasitism from generalist egg parasitoids (based on the low number of Trichogramma sp.…”

“…collected from 2012 surveys) does not significantly contribute to A. auroguttatus egg mortality. Predation of A. auroguttatus eggs (i.e., total number of missing and chewed eggs) during natural enemy surveys contributed 16-24% to sentinel egg mortality in 2012 (Lopez & Hoddle, 2013), and 14-22% in 2013, indicating that generalist predators consume considerable numbers of eggs. However, these results are likely exaggerated due to the ready and concentrated availability of the sentinel eggs deployed during these studies.…”

“…Trees were considered infested if symptoms described in Hishinuma et al (2011) such as larval galleries and exit holes were present. At each selected tree, sentinel eggs were deployed into non-caged and caged treatments ( Figure 1; individually suspended on each of 10 A. auroguttatus-infested trees, for a total of 20 egg-infested oak branches deployed at each field site), as these treatment types were shown to be equally suitable for detecting natural enemies of A. auroguttatus eggs (Lopez & Hoddle, 2013). The deployment of A. auroguttatus eggs at each site was conducted over an eight-week period during 26 June-14 August 2013.…”

“…Egg-infested oak branches were positioned in the centre of the cage, so that no contact was made between the branch and cage walls. Sentinel egg masses were deployed into non-caged and caged treatments and were retrieved, reared and examined as described in Lopez and Hoddle (2013). …”

“…Due to the inability to rear A. auroguttatus, and thus determine the specificity of natural enemies attacking its larvae and pupae, search efforts have focused on natural enemies attacking A. auroguttatus eggs. Egg parasitoids have shown potential as biological control agents of Agrilus planipennis and other Agrilus woodborers (Liu et al, 2007;Taylor, Duan, Fuester, Hoddle, & Van Driesche, 2012), and these natural enemies, should they exist for A. auroguttatus, would be of high interest for use in a biological control programme for this pest (Lopez & Hoddle, 2013). The goal of this work was to expand upon previous surveys (Lopez & Hoddle, 2013) throughout the native and introduced range of A. auroguttatus by deploying sentinel egg masses in south-eastern Arizona and southern California to attract, collect and identify potential egg parasitoids.…”