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 suppres- sion, partly because evolution of resistance to predators and parasitoids is prevented by several factors (e.g., spatial or tempo- ral 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 years 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. NZD $ 160m p.a.). 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 years (14 host generations) following parasitoid introduction, despite re- leases 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 pastures, but not 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

Asymmetry in reproduction strategies drives evolution of resistance in biological control systems

© 2018 Casanovas et al. This is an open access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited. The success of biological control may depend on the control agent co-evolving with its target pest species, precluding the emergence of resistance that often undermines chemical control. However, recent evidence of a decline in attack rates of a sexual pest weevil by its asexual parasitoid suggests that evolutionary arms races may not prevent the emergence of resistance if the host and parasitoid do not have reproductive strategies that generate equal amounts of genetic variation. To understand how these asymmetries in reproductive strategies may drive the emergence of resistance, we combined life history data from two pest weevils and their parasitoids (one sexual and one asexual) in the New Zealand pastoral ecosystem, with a population dynamic model that allows the coevolution of hosts and parasitoids. We found that the ratio of the genetic variance of hosts to parasitoids was a key determinant of the emergence of resistance. Host resistance eventually occurred unless the parasitoids had considerably greater additive genetic variance than their host. The higher reproductive rate of asexual parasitoids did little to offset the cost of reduced additive genetic variance. The model predictions were congruent with long-term parasitism rates observed in the field for both of the pests considered (one with a sexual and one with an asexual parasitoid). We then explored the consequences of introducing two parasitoids with different reproductive strategies that attack the same sexual host. The model showed that the sexually reproducing parasitoid always out-competed the asexually reproducing one. Our study shows that any asymmetry in reproductive strategies is extremely important for predicting the long-term success of biological control agents. Fortunately, introduction of sexually reproducing individuals after an initial introduction of asexual strains may overcome the problems of host resistance. We conclude that evolution must be considered when evaluating the long-term outcomes of importation biological control

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

© The Author(s) 2020. 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

New Zealand pest management: current and future challenges

New Zealand is under increasing pressure from terrestrial and aquatic pests, weeds and diseases that threaten the country's ecosystems and economy. Ongoing improvement in existing pest management methodologies and novel approaches are required in response to public concerns about animal welfare, increasingly stringent trade requirements, abolition of groups of pesticides and resistance to existing pesticides as well as, possibly, biological control agents. Surveillance and pest monitoring are needed to increase the chances of early interception of invasive species or to confirm their eradication. Core capabilities in taxonomy, genomics, phenology, ecology, pest impacts, development of novel control tools and social science are required and must be maintained nationally. Given New Zealand's unique environment, the ecology of invasive pests cannot be presumed to be the same as that in their native ranges, yet currently many pests in New Zealand are managed with poor understanding of their bionomics and impacts. Failure to address these areas will have serious adverse impacts on New Zealand