Calibration of laboratory derived indices for non-target arthropod risk assessment with field data for plant protection products.

The Hazard Quotient (HQ) compares field application rate to intrinsic toxicity assessed with sensitive indicator species. As a hazard indicator for risk assessment, the HQ must be calibrated against measured effects under field conditions. Because protection goals may be context specific, we analyse how choice of acceptance criteria affects setting of the HQ and calibrate HQ for various scenarios under the strict condition that no false negative conclusions may be reached. We use Non-Target Arthropod toxicity data from laboratory studies on inert (Tier 1) and on natural substrates (Tier 2) and calibrate the HQ using application rates and arthropod abundance counts from field studies in orchards, arable fields, and hay meadows in 34 locations in Western Europe. With 21 formulations (17 active substances) tested in mostly multi-rate field studies, our reference data base has 120/121 values at Tier 1/Tier 2, respectively. We use the Proportion of Affected Taxa and Duration of Effect to jointly define acceptance criteria, starting with No Observed Effects. Absence of field effects is correctly predicted with HQ < 1.3 at Tier 1 and HQ < 0.48 at Tier 2, but these settings result in a high proportion of false positive outcomes. Increasing accepted duration of effect from 0 to 4 to 8 weeks results in HQ-threshold changes from 1.3 to 6.4 to 250 for Tier 1 studies and from 0.48 to 1.1 to 5.7 for Tier 2 studies. This coincides with a clear decrease in false positive outcomes. Recovery within a year is correctly concluded for 73% of the products passing the corresponding Tier 1 HQ < 2600 and for 92% of products at Tier 2 (HQ <230). Our analysis shows that the calibration is appropriate for a broad geographical range, for in-field and off-field situations and for phytophagous and non-phytophagous species alike.

Can pollen headspace volatiles and pollenkitt lipids serve as reliable chemical cues for bee pollinators?

Chemical analysis of putative contact chemical cues for pollinators from pollen of two plant species, Ranunculus bulbosus (Ranunculaceae) and Campanula rapunculoides (Campanulaceae), showed high consistency in the qualitative and quantitative composition of pollenkitt surface lipids in all samples analyzed per species. The pollenkitt lipids of R. bulbosus included an aldehyde, fatty acid amides, saturated and unsaturated hydrocarbons, and secondary alcohols; the lipids of C. rapunculoides consisted of an aldehyde, monoketones, and ß-diketones. In marked contrast, the pollen headspace volatiles showed a wide qualitative and quantitative variability among all samples per species, whereby the variability was more pronounced in R. bulbosus. Hence, the highly species-specific pollenkitt lipids may provide pollinators with more reliable information on pollen identity.

Body temperature of the parasitic wasp Pimpla turionellae (Hymenoptera) during host location by vibrational sounding.

The pupal parasitoid Pimpla turionellae (L.) uses self-produced vibrations transmitted on the plant substrate, so-called vibrational sounding, to locate immobile concealed pupal hosts. The wasps are able to use vibrational sounding reliably over a broad range of ambient temperatures and even show an increased signal frequency and intensity at low temperatures. The present study investigates how control of body temperature in the wasps by endothermic mechanisms may facilitate host location under changing thermal environments. Insect body temperature is measured with real-time IR thermography on plant-stem models at temperature treatments of 10, 18, 26 and 30 °C, whereas behaviour is recorded with respect to vibrational host location. The results reveal a low-level endothermy that likely interferes with vibrational sound production because it occurs only in nonsearching females. At the lowest temperature of 10 °C, the thoracic temperature is 1.15 °C warmer than the ambient surface temperature whereas, at the high temperatures of 26 and 30 ° C, the wasps cool down their thorax by 0.29 and 0.47 °C, respectively, and their head by 0.45 and 0.61 °C below ambient surface temperature. By contrast, regardless of ambient temperature, searching females always have a slightly elevated body temperature of at most 0.30 °C above the ambient surface temperature. Behavioural observations indicate that searching females interrupt host location more frequently at suboptimal temperatures, presumably due to the requirements of thermoregulation. It is assumed that both mechanisms, producing vibrations for host location and low-level endothermy, are located in the thorax. Endothermy by thoracic muscle work probably disturbs signal structure of vibrational sounding, so the processes cannot be used at the same time.

Temperature affects interaction of visual and vibrational cues in parasitoid host location.

Parasitoid host location in nature is facilitated by simultaneously using different information sources. How multisensory orientation on the same spatial scale is influenced by environmental conditions is however poorly understood. Here we test whether changes in reliability of cues can cause parasitoids to alter multisensory orientation and to switch to cues that are more reliable under extreme temperatures. In the ichneumonid wasp Pimpla turionellae, multisensory use of thermally insensitive vision and thermally sensitive mechanosensory host location by vibrational sounding (echolocation on solid substrate) was investigated with choice experiments on plant-stem models under optimum temperature (18 degrees C), at high- (28 degrees C) and low-temperature limits (8 degrees C) of vibrational sounding. Temperature affected relative importance of vibrational sounding whereas visual orientation did not vary. At 18 degrees C, parasitoids used visual and vibrational cues with comparable relative importance. At 8 and 28 degrees C, the role of vibrational sounding in multisensory orientation was significantly reduced in line with decreased reliability. Wasps nearly exclusively chose visual cues at 8 degrees C. The parasitoids switch between cues and sensory systems depending on temperature. As overall precision of ovipositor insertions was not affected by temperature, the parasitoids fully compensate the loss of one cue provided another reliable cue is available on the same spatial scale.