Invertebrate Biosecurity Challenges in High-Productivity Grassland: The New Zealand Example

Use of mixed-type data clustering algorithm for characterizing temporal and spatial distribution of biosecurity border detections of terrestrial non-indigenous species

Appropriate inspection protocols and mitigation strategies are a critical component of effective biosecurity measures, enabling implementation of sound management decisions. Statistical models to analyze biosecurity surveillance data are integral to this decision-making process. Our research focuses on analyzing border interception biosecurity data collected from a Class A Nature Reserve, Barrow Island, in Western Australia and the associated covariates describing both spatial and temporal interception patterns. A clustering analysis approach was adopted using a generalization of the popular k-means algorithm appropriate for mixed-type data. The analysis approach compared the efficiency of clustering using only the numerical data, then subsequently including covariates to the clustering. Based on numerical data only, three clusters gave an acceptable fit and provided information about the underlying data characteristics. Incorporation of covariates into the model suggested four distinct clusters dominated by physical location and type of detection. Clustering increases interpretability of complex models and is useful in data mining to highlight patterns to describe underlying processes in biosecurity and other research areas. Availability of more relevant data would greatly improve the model. Based on outcomes from our research we recommend broader use of cluster models in biosecurity data, with testing of these models on more datasets to validate the model choice and identify important explanatory variables.

The phytosanitary risks posed by seeds for sowing trade networks

When successful, the operation of local and international networks of crop seed distribution or “seed systems” ensures farmer access to seed and impacts rural livelihoods and food security. Farmers are both consumers and producers in seed systems and benefit from access to global markets. However, phytosanitary measures and seed purity tests are also needed to maintain seed quality and prevent the spread of costly weeds, pests and diseases, in some countries regulatory controls have been in place since the 1800s. Nevertheless, seed contaminants are internationally implicated in between 7% and 37% of the invasive plant species and many of the agricultural pests and diseases. We assess biosecurity risk across international seed trade networks of forage crops using models of contaminant spread that integrate network connectivity and trade volume. To stochastically model hypothetical contaminants through global seed trade networks, realistic dispersal probabilities were estimated from quarantine weed seed detections and incursions from border security interception data in New Zealand. For our test case we use contaminants linked to the global trade of ryegrass and clover seed. Between 2014 and 2018 only four quarantine weed species (222 species and several genera are on the quarantine schedule) warranting risk mitigation were detected at the border. Quarantine weeds were rare considering that average import volumes were over 190 tonnes for ryegrass and clover, but 105 unregulated contaminant species were allowed in. Ryegrass and clover seed imports each led to one post-border weed incursion response over 20 years. Trade reports revealed complex global seed trade networks spanning >134 (ryegrass) and >110 (clover) countries. Simulations showed contaminants could disperse to as many as 50 (clover) or 80 (ryegrass) countries within 10 time-steps. Risk assessed via network models differed 18% (ryegrass) or 48% (clover) of the time compared to risk assessed on trade volumes. We conclude that biosecurity risk is driven by network position, the number of trading connections and trade volume. Risk mitigation measures could involve the use of more comprehensive lists of regulated species, comprehensive inspection protocols, or the addition of field surveillance at farms where seed is planted.

Approaches for estimating benefits and costs of interventions in plant biosecurity across invasion phases

Nonnative plant pests cause billions of dollars in damages. It is critical to prevent or reduce these losses by intervening at various stages of the invasion process, including pathway risk management (to prevent pest arrival), surveillance and eradication (to counter establishment), and management of established pests (to limit damages). Quantifying benefits and costs of these interventions is important to justify and prioritize investments and to inform biosecurity policy. However, approaches for these estimations differ in (1) the assumed relationship between supply, demand, and prices, and (2) the ability to assess different types of direct and indirect costs at invasion stages, for a given arrival or establishment probability. Here we review economic approaches available to estimate benefits and costs of biosecurity interventions to inform the appropriate selection of approaches. In doing so, we complement previous studies and reviews on estimates of damages from invasive species by considering the influence of economic and methodological assumptions. Cost accounting is suitable for rapid decisions, specific impacts, and simple methodological assumptions but fails to account for feedbacks, such as market adjustments, and may overestimate long-term economic impacts. Partial equilibrium models consider changes in consumer and producer surplus due to pest impacts or interventions and can account for feedbacks in affected sectors but require specialized economic models, comprehensive data sets, and estimates of commodity supply and demand curves. More intensive computable general equilibrium models can account for feedbacks across entire economies, including capital and labor, and linkages among these. The two major considerations in choosing an approach are (1) the goals of the analysis (e.g., consideration of a single pest or intervention with a limited range of impacts vs. multiple interventions, pests or sectors), and (2) the resources available for analysis such as knowledge, budget and time.

Volatile and Contact Chemical Cues Associated with Host and Mate Recognition Behavior of Sphenophorus venatus and Sphenophorus parvulus (Coleoptera: Dryophthoridae)

Beetles in the genus Sphenophorus Schönherr, or billbugs, potentially utilize both volatile and non-volatile behavior-modifying chemical signals. These insects are widely distributed across North America, often occurring in multi-species assemblages in grasses. However, details about their host- and mate-finding behavior are poorly understood. This study tested the hypothesis that volatile organic compounds from host-plants and conspecifics direct the dispersal behavior of hunting billbug S. venatus Say. Further, we characterized the cuticular hydrocarbon profiles of two widespread pest species, S. venatus and bluegrass billbug S. parvulus Gyllenhaal, to assess the potential role of contact pheromones in mate-recognition. In Y-tube olfactometer bioassays, S. venatus males were attracted to a combination of conspecifics and Cynodon dactylon host-plant material, as well as C. dactylon plant material alone. S. venatus females were attracted to a combination of male conspecifics and host-plants but were also attracted to male conspecifics alone. Field evaluation of a putative male-produced aggregation pheromone, 2-methyl-4-octanol, identified from two congeners, S. levis Vaurie and S. incurrens Gyllenhaal, did not support the hypothesis that S. venatus and S. parvulus were also attracted to this compound. Gas chromatography-mass spectrometry analysis of S. venatus and S. parvulus whole-body cuticular extracts indicated a series of hydrocarbons with qualitative and quantitative interspecific variation in addition to intraspecific quantitative variation between males and females. This study provides the first evidence that S. venatus orients toward host- and insect-derived volatile organic compounds and substantiates the presence of species-specific cuticular hydrocarbons that could serve as contact pheromones for sympatric Sphenophorus species.