Preference of a native beetle for "exoticism," characteristics that contribute to invasive success of Costelytra zealandica (Scarabaeidae: Melolonthinae)

Knockdown of a chemosensory protein disrupts soil-guided behavior of a subterranean larval pest

In recent years, RNA interference (RNAi) has become a widely studied tool for the functional analysis of genes and more recently, for pest control. Hylamorpha elegans (Coleoptera: Scarabaeidae) is a beetle endemic to Chile, considered an important pest during its larval stage as white grubs, feeding on organic matter (OM) and crop roots (e.g., wheat and red clover). Its control is limited due to its subterranean behavior. Thus, studying a chemosensory system as a fundamental part of the transport and recognition of chemicals from the environment could provide new targets for the knowledge and control of this beetle. Recently, chemosensory genes have been identified for H. elegans white grubs, and a chemosensory protein (CSP) was selected. This study aimed to evaluate the functional role of a highly expressed CSP in the subterranean behavior of white grubs. For this purpose, food preference assays were performed and standardized. Afterward, double-stranded RNA (dsRNA) was synthesized based on a selected CSP. A chosen preference assay was conducted using white grubs treated with dsRNA. Findings showed that white grubs prefer peat with high OM over red clover roots. Additionally, the CSP gene is upregulated when OM content increases. Finally, the knockdown of the CSP led to a disruption in soil-guided behavior. This protein may represent a novel target to be studied in the frame of management strategies for H. elegans.

Host Range Expansion of an Endemic Insect Herbivore is Associated With High Nitrogen and Low Fibre Content in Exotic Pasture Plants

Endemic moth species of the genus Wiseana spp. (Hepialidae) have become serious pests of introduced pasture plants in New Zealand. The original native host plants of these moths have not been confirmed. This study investigated the performance (survival, development time, weight gain) of three Wiseana species on seven putative host plants: five native and two exotic species. The aim was to identify native hosts for the three Wiseana species and to compare their performance on native plants and exotic pasture plants. The chemical composition of the seven putative host plants was investigated to compare native and exotic plant chemistries, and to test for associations between plant characteristics and performance of selected Wiseana species. Carbon, nitrogen, silica and fibre contents were measured for each plant species; primary metabolite composition was determined by gas chromatography-mass spectrometry. For the three moth species, increased survival and weight gain were significantly associated with high nitrogen and low fibre contents in one exotic host plant, white clover (Trifolium repens), although one species, W. umbraculata, did not complete development to adult on any of the plants tested, including clover. Two exotic plants (T. repens, Lolium perenne × Lolium multiflorum), and two native plants (Aciphylla squarrosa and Festuca actae) supported W. copularis development to the adult stage, but only one exotic (T. repens) and one native (F. actae) species supported complete development of W. cervinata. Exotic and native plant species had distinct metabolite profiles, but there was no significant association between metabolite composition and Wiseana performance. We conclude that W. copularis and W. cervinata, but not W. umbraculata, have expanded their host range, because of their ability to use both native and new hosts. No evidence was found for a host shift, i.e., a loss of performance on the ancestral host compared with the new host.

Severe Insect Pest Impacts on New Zealand Pasture: The Plight of an Ecological Outlier

New Zealand's intensive pastures, comprised almost entirely introduced Lolium L. and Trifolium L. species, are arguably the most productive grazing-lands in the world. However, these areas are vulnerable to destructive invasive pest species. Of these, three of the most damaging pests are weevils (Coleoptera: Curculionidae) that have relatively recently been controlled by three different introduced parasitoids, all belonging to the genus Microctonus Wesmael (Hymenoptera: Braconidae). Arguably that these introduced parasitoids have been highly effective is probably because they, like many of the exotic pest species, have benefited from enemy release. Parasitism has been so intense that, very unusually, one of the weevils has now evolved resistance to its parthenogenetic parasitoid. This review argues that New Zealand's high exotic pasture pest burden is attributable to a lack of pasture plant and natural enemy diversity that presents little biotic resistance to invasive species. There is a native natural enemy fauna in New Zealand that has evolved over millions of years of geographical isolation. However, these species remain in their indigenous ecosystems and, therefore, play a minimal role in creating biotic resistance in the country's exotic ecosystems. For clear ecological reasons relating to the nature of New Zealand pastures, importation biological control can work extremely well. Conversely, conservation biological control is less likely to be effective than elsewhere.