Identification of plant semiochemicals and evaluation of their interactions with early spring insect pests of asparagus

<p>Information is lacking on the chemical ecology of asparagus, and knowledge about the effects of its volatile emissions on its associated early season pest species is completely absent. The current study aimed to (1) evaluate whether the asparagus miner responds to asparagus volatiles, (2) identify and compare the changes in asparagus host plant volatiles from mechanical and chewing damage by the black cutworm, a temporally co-occurring species with the asparagus miner, and (3) assess how asparagus volatiles affect asparagus miner populations in the field. Results indicated that asparagus miners were significantly attracted to healthy asparagus stems when compared to clean air. Damaged asparagus headspace volatiles were quantitatively and qualitatively different from healthy plants. Volatile baits elicited a range of responses, but their effects were inconsistent between sampling years and phenology-dependent. Overall, we demonstrated that the chemical ecology of asparagus may be altered by its pest community, and volatiles identified from asparagus may impact the behavior of the asparagus miner.</p

Reported neonicotinoid use in a survey of commercial potato farmers in Wisconsin, 2003–2006.

<p>Reported neonicotinoid use in a survey of commercial potato farmers in Wisconsin, 2003–2006.</p

Potato production history.

<p>Potato incidence on cultivated cropland over four consecutive years of prior production estimated from within a 1.5 km radius surrounding each sample field centroid (N = 50 fields). Frequency of production shows that farmers often rotate potato at variable time intervals, ranging from low intensity production (potato occurring once in four years) to high intensity production (continuous potato).</p

Potato production history and imidacloprid resistance.

<p>Average lethal concentration responses of <i>L</i>. <i>decemlineata</i> populations to imidacloprid compared to frequency of potato production in bioassay collection fields (N = 50 populations). Years of potato production indicate the number of potato crops grown during the four years preceding the bioassay year. Error bars represent 95% confidence intervals of the mean. Numbers in parentheses represent the count of fields in each group.</p

Spatial and Temporal Potato Intensification Drives Insecticide Resistance in the Specialist Herbivore, <i>Leptinotarsa decemlineata</i>

<div><p>Landscape-scale intensification of individual crops and pesticide use that is associated with this intensification is an emerging, environmental problem that is expected to have unequal effects on pests with different lifecycles, host ranges, and dispersal abilities. We investigate if intensification of a single crop in an agroecosystem has a direct effect on insecticide resistance in a specialist insect herbivore. Using a major potato pest, <i>Leptinotarsa decemlineata</i>, we measured imidacloprid (neonicotinoid) resistance in populations across a spatiotemporal crop production gradient where potato production has increased in Michigan and Wisconsin, USA. We found that concurrent estimates of area and temporal frequency of potato production better described patterns of imidacloprid resistance among <i>L</i>. <i>decemlineata</i> populations than general measures of agricultural production (% cropland, landscape diversity). This study defines the effects individual crop rotation patterns can have on specialist herbivore insecticide resistance in an agroecosystem context, and how impacts of intensive production can be estimated with general estimates of insecticide use. Our results provide empirical evidence that variation in the intensity of neonicotinoid-treated potato in an agricultural landscape can have unequal impacts on <i>L</i>. <i>decemlineata</i> insecticide insensitivity, a process that can lead to resistance and locally intensive insecticide use. Our study provides a novel approach applicable in other agricultural systems to estimate impacts of crop rotation, increased pesticide dependence, insecticide resistance, and external costs of pest management practices on ecosystem health.</p></div

Potato intensity and imidacloprid resistance.

<p>Potato intensity metric (PIM) is log-linearly, positively related to the incidence of imidacloprid resistance in sampled populations of <i>L</i>. <i>decemlineata</i> (N = 50 populations). PIM is a metric that accounts for both area and history of potato production. Shading illustrates 95% confidence intervals of the mean. Circle (●) data points represent Michigan and triangles (▲) represent Wisconsin.</p

Conceptual diagram of cultivated cropland and potato measurements.

<p><b>(a)</b> Yellow fields represent the area of cultivated cropland in the landscape. Cultivated cropland was divided by the total landscape area to measure the proportion of the ecosystem used for agriculture. <b>(b)</b> Purple fields represent the available cropland used for potato production in the year <i>L</i>. <i>decemlineata</i> populations were collected. Proportion current potato was calculated by dividing area of purple fields by area of yellow fields. <b>(c)</b> Red fields represent the area of cropland used for potato production in at least one of the four years preceding the <i>L</i>. <i>decemlineata</i> collection year for bioassays. Proportion potato in time was calculated by dividing the area of red fields by area of yellow fields. <b>(d)</b> The gradient of blue colored fields represents the frequency of potato production on fields that had historically been potato in one to four years before the bioassay. Light to dark blue represents an increase in planting frequency over years. Each of these areas was used to calculate the potato intensity metric (PIM).</p

Parameter estimates (±SE), AIC and difference in AIC from best models fitting log transformed LC₅₀ estimates of resistance in <i>L</i>. <i>decemlineata</i> populations.

<p>^a Parameter estimate differs significantly from zero (*, <i>P</i> < 0.05)</p><p>^b Proportion potato grown on available cropland in the year bioassays were conducted</p><p>^c Proportion cultivated cropland where potato was grown at least once in the four years preceding the bioassay</p><p>^d Represents the interaction between specified model parameter and state</p><p>Parameter estimates (±SE), AIC and difference in AIC from best models fitting log transformed LC₅₀ estimates of resistance in <i>L</i>. <i>decemlineata</i> populations.</p