Olfactory responses of Argentine stem weevil to herbivory and endophyte-colonisation in perennial ryegrass

Argentine stem weevil adults (ASW, Listronotus bonariensis) feed on the leaves of agricultural grasses and their larvae mine the pseudostem, causing extensive damage that can result in plant death. Plants emit volatiles that serve as signals to host-searching insects and these odours can be altered by both herbivory and fungal endophyte-infection. This study investigated whether ASW adults utilise olfaction to identify their host plants, perennial ryegrass (Lolium perenne), and if conspecific herbivory or the presence of Epichloë festucae var. lolii fungal endophytes (strain wild-type or AR1) influenced such responses. Results from olfactometer bioassays established that ASW adults were able to utilise their olfactory response to orient towards volatiles released by perennial ryegrass and further, the weevils displayed a preference for plants previously damaged by conspecific weevils. However, there was no evidence that weevils had the ability to distinguish between endophyte-infected and endophyte-free plants using olfaction alone. Using a push–pull extraction technique, thirteen volatile compounds were identified in the blend released by perennial ryegrass. Endophyte and herbivory were found to alter these volatile compounds and quantities emitted by this forage grass. This study suggests that despite observing differences in the plant volatile blend, ASW do not perceive endophyte (wild-type and AR1) using olfaction alone and must rely on other cues, e.g. contact chemoreception or post-ingestional malaise, to detect the presence of a bioactive endophyte in an otherwise acceptable host plant.

Ploidy in Lolium spp. cultivars affects Argentine stem weevil parasitism by Microctonus hyperodae

A laboratory study was conducted to: (1) advance earlier work to determine the susceptibility of Listronotus bonariensis (Argentine stem weevil) to its parasitoid biological control agent, Microctonus hyperodae, in the presence of diploid ryegrasses such as Lolium multiflorum or Lolium perenne; and (2) determine whether or not plant orientation (i.e. horizontal vs. vertical) had any effect on parasitism rates. No significant differences in parasitism rates were found in the Listronotus bonariensis populations in the two grasses. However, combining and analysing these data with those from an earlier experiment conducted in the same way showed that parasitism rates were significantly lower in diploid Lolium multiflorum cultivars than in tetraploid Lolium multiflorum. This is the first clear evidence of a ploidy effect on parasitism rates in the presence of Lolium multiflorum. Tetraploid Lolium multiflorum has fewer, more robust and larger tillers than the diploid Lolium spp. so higher parasitism rates may be related to the lack of hiding places for an evasive genetically-driven behaviourally-based resistance by Listronotus bonariensis.

Intensified agriculture favors evolved resistance to biological control

Increased regulation of chemical pesticides and rapid evolution of pesticide resistance have increased calls for sustainable pest management. Biological control offers sustainable pest suppression, partly because evolution of resistance to predators and parasitoids is prevented by several factors (e.g., spatial or temporal refuges from attacks, reciprocal evolution by control agents, and contrasting selection pressures from other enemy species). However, evolution of resistance may become more probable as agricultural intensification reduces the availability of refuges and diversity of enemy species, or if control agents have genetic barriers to evolution. Here we use 21 y of field data from 196 sites across New Zealand to show that parasitism of a key pasture pest (Listronotus bonariensis; Argentine stem weevil) by an introduced parasitoid (Microctonus hyperodae) was initially nationally successful but then declined by 44% (leading to pasture damage of c. 160 million New Zealand dollars per annum). This decline was not attributable to parasitoid numbers released, elevation, or local climatic variables at sample locations. Rather, in all locations the decline began 7 y (14 host generations) following parasitoid introduction, despite releases being staggered across locations in different years. Finally, we demonstrate experimentally that declining parasitism rates occurred in ryegrass Lolium perenne, which is grown nationwide in high-intensity was significantly less than in adjacent plots of a less-common pasture grass (Lolium multiflorum), indicating that resistance to parasitism is host plant–dependent. We conclude that low plant and enemy biodiversity in intensive large-scale agriculture may facilitate the evolution of host resistance by pests and threaten the long-term viability of biological control.

Effect of Epichlo endophyte strains in Lolium spp cultivars on Argentine stem weevil parasitism by Microctonus hyperodae

This paper reports on an extensive field investigation conducted at Lincoln during the 20142015 summer/early autumn This aimed to assess the effects of a range of novel Epichlo endophytes when present in different cultivars of Lolium spp on parasitism rates by the biological control agent Microctonus hyperodae in Listronotus bonariensis (ie the Argentine stem weevil) Results for the entire summer and including all treatment combinations did not find any significant differences in parasitism in L bonariensis populations However in the early autumn independent of the endophytes present significantly higher levels of parasitism were found in a tetraploid Lolium multiflorum cultivar and a tetraploid L perenne selection compared to the L perenne cultivars Whether this finding has any bearing on a possible mechanism of weevil resistance is discussed

Can pest management and biosecurity benefit from the surveillance and security industries

Selfreporting cameras have the potential to revolutionise the trapping networks utilised in pest management and biosecurity A study was carried out to determine whether commercially available selfreporting camera systems that use WiFi and GSM to transmit images to secure websites could be incorporated into trapping networks Of 45 systems initially examined one the RedEye security camera was laboratory tested Tests showed that the standard optics package was incapable of distinguishing between clover root weevil (Sitona lepidus) and Argentine stem weevil (Listronotus bonariensis) An upgrade of the cameras optics enabled it be used to successfully monitor porina (Wiseana spp) flight activity While this result was encouraging more research is needed before the technology can be incorporated into trapping networks In particular further thought is needed as to the level of image resolution that is required to ensure that the system is relevant to all pest management and biosecurity practitioners