A proposal to use plant demographic data to assess potential weed biological control agents impacts on non-target plant populations

Abstract

Weed biocontrol programs aim to reduce the spread and population growth rate of the target plant while stabilizing or increasing populations of those native species considered under threat by invasive plants. This goal is not unique to weed biocontrol but applies to all other invasive plant management techniques, though such information is rarely collected. Without this information, success of management interventions can be ambiguous, and regulatory agencies, the public, policy makers, funders and land managers cannot be held accountable for chosen treatments. A fundamental reform, including use of demographic studies and long-term assessments, are essential to guide weed biocontrol programs. We propose to add use of plant demography (an assessment of how environmental factors and ecological interactions, for example competition, disease or herbivory, may affect plant populations by altering survival, growth, development and reproductive rates of plant individuals) during host specificity risk assessments of potential biological control agents. Demographic models can refine assessments of potential impacts for those plant species that experience some feeding or larval development during host specificity testing. Our proposed approach to focus on impact on plant demography instead of attack on plant individuals is useful in appropriately gauging threats potential weed biocontrol agents may pose to non-target species after field release.

When misconceptions impede best practices: evidence supports biological control of invasive Phragmites

“…While biocontrol scientists and others have documented non-target attack by released biocontrol agents (Hinz et al 2019), there are only two examples of biocontrol agents (out of nearly 500 species that were released worldwide) that have had (predictable) demographic consequences on nontarget species. A full discussion of the history of host specificity testing and non-target attack is available elsewhere (Blossey et al 2018a;Suckling and Sforza 2014) Finally, we once again reject the comparison of the two Archanara species with several other accidentally introduced Phragmites herbivores that are spreading in North America and now attack P. australis americanus. There are other European species that have retained their sub-species level specificity and are never found on P. australis americanus and several North American Phragmites herbivores that have not switched to introduced P. australis australis (Blossey 2003;Park and Blossey 2008).…”

“…This however, contradicts the generally acknowledged standard for the review of biological control agents and the Endangered Species Act which interpret harm and risk at the population level (i.e. interpreted using demography and population dynamics) (Blossey et al 2018a;Campbell et al 2002;Davis et al 2006). Under this standard, attack-and potentially even death-of individual non-target plants is acceptable as long as the populations of those individuals do not decline, which makes strong ecological and evolutionary sense.…”

Education, Training and Capacity-Building in the Field of Biological Invasions in South Africa

“…19) without a single example of an agent exhibiting unexpected non-target impacts on other species, this type of hyperbole undermines modern biocontrol. A few examples of non-target impacts of biological control agents are known from other countries, but these also are generally overstated (Blossey et al 2018). However, a local textbook from a different publisher has two pages of accurate descriptions of alien plants, their means of introduction and effects on ecosystems and biodiversity.…”

Constraints in weed biological control: contrasting responses by implementing nations

“…Given the protracted problems facing weed biocontrol in the USA and Hawaii, especially, it is not surprising that the emphasis in this Special Issue is provided by authors from the USA writing on risk assessments, conflicts of interest and regulations, and on the considerable complications of dealing with agenthost-fidelity for taxa at sub-specific levels (Bean and Dudley 2018;Casagrande et al 2018;Smith et al 2018), and on innovations to expand host-specificity procedures, to help make them more definitive (Park et al 2018;Blossey et al 2018). Two papers in this Special Issue have wide applicability: Schaffner et al (2018) review and assess the use of open-field testing in risk assessments, and Blossey et al (2018) argue that the use of long-term, plant demographic data should be an essential practical and conceptual component in debates on host-specificity, risk assessments, and in the evaluation of weed biological control in management programs. Presenting a glimpse of the obverse of the coin, two further papers highlight successful contributions to weed biological control in the USA: Pitcairn (2018) summarizes the history of successes in California; and Weed et al (2018) document contemporary progress with weed biocontrol in Idaho, through the engagement of 'citizenscientists' and the general community.…”