Influence of temperature on host location and multisensory orientation in the parasitoid Pimpla turionellae (L.) (Hymenoptera)

The ichneumonid wasp Pimpla turionellae (L.) (Hymenoptera) is a specialist parasitoid of lepidopteran pupae, and has to overcome the challenge of reduced chemical and visual cues as pupae are immobile, do not feed and do not emit excrements. Certain hymenopteran species have developed a particular mechanosensory mechanism in order to locate hosts hidden in hollow spaces inside of plant material (Broad & Quicke 2000). Similar to echolocation they use self-produced vibrations, instead of sounds, that are transmitted by the antennae onto the substrate. In analogous way to acoustics, this mechanosensory mechanism is referred to as vibrational sounding (Wäckers & al. 1998). Thermal dependence is well known in acoustical and vibrational communication of arthropods (e.g. Pires & Hoy 1992, Shimizu & Barth 1996) and is likewise presumed to affect mechanosensory host location by vibrational sounding. The species P. turionellae has recently been found to use vibrational sounding successfully in a temperature range from 8 to 28°C, but with less performance of searching behaviour and an adjusted signal production at extreme temperatures (Kroder & al. 2006, & al. 2007b, Samietz & al. 2006). Many insects have evolved strategies to maintain a balance of body temperature by ecto- and endothermic means. Raising and maintaining body temperatures above the ambient environment by endothermic means is particularly known in several hymenopteran species (Heinrich 1993). In the case of a thermally influenced host location mechanism, such means of thermoregulation could be supposed as well in order to maintain performance with changing temperatures. The study elucidates if the wasps are able to regulate their body temperature at suboptimal conditions during vibrational sounding and furthermore examines the role of vibrational sounding in multisensory orientation at different ambient temperatures.Die Schlupfwespe Pimpla turionellae parasitiert versteckte Lepidopterenpuppen und orientiert sie sich bei der Wirtssuche multisensorisch mittels visueller Reize und aktiver Vibrationsortung mit selbst produzierten Schwingungen (Vibrational-Sounding). Die Studie untersucht, inwieweit die Wespen bei Änderung der Umgebungstemperaturen von 8-26°C (1) zwischen der temperatur-sensitiven vibratorischen und der -insensitiven visuellen Orientierung wechseln und (2) gegebenenfalls selbst die Körpertemperatur regulieren können, um die sehr präzise Vibrationsortung bei niedrigen Temperaturen aufrechtzuerhalten. Messungen mit Infrarot-Thermographie zeigen, dass suchende Wespen leicht erhöhte Körpertemperaturen während der vibratorischen Wirtssuche aufweisen, welche auf metabolische Wärmeproduktion zurückzuführen sind. Wahlexperimente unter kontrollierten Temperaturen zeigen zudem, dass die Nutzung der temperatur-sensitiven vibratorischen Reize bei pessimalen Temperaturen abnimmt und die Wespen auf fast ausschließliche visuelle Orientierung wechseln. Folglich wird die Relevanz einzelner Reize bei der multisensorischen Orientierung direkt vom Faktor Temperatur beeinflusst. Solange ein zuverlässiger Reiz vorhanden ist, nimmt dabei auch die Präzision der Lokalisation insgesamt nicht ab

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°C), at high- (28°C) and low-temperature limits (8°C) of vibrational sounding. Temperature affected relative importance of vibrational sounding whereas visual orientation did not vary. At 18°C, parasitoids used visual and vibrational cues with comparable relative importance. At 8 and 28°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°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 scal

Evaluation of honey bee larvae data: sensitivity to PPPs and impact analysis of EFSA Bee GD

In addition to other assessments, the EFSA bee guidance document (2013) requires the risk assessment of plant protection products on honey bee larvae. At the time the EFSA GD was finalized, no data on honey bee larvae were available due to absence of suitable methods. That is why in 2013 the European Crop Protection Association (ECPA) perfomed an impact analysis of the new EFSA risk assessment, using extrapolated endpoints derived from acute oral honey bee endpoints. Today, a number of honey bee larvae toxicity studies (138 active substances or formulated products) have been conducted according to the newly developed testing methods for single exposure (OECD TG 237) repeated exposure studies until the end of the larval development (D7/D8) and repeated exposure testing (OECD GD 239) until adult hatch (D22). These experimental data have been used to determine the ‘pass rates’ for 215 worst case uses (72 fungicide spray and solid uses, 91 herbicide spray uses, incl. 8 PGR uses and in total 52 insecticide spray and solid uses, incl. 2 nematicide and 3 IGR uses) according to the EFSA Bee GD and to compare with the original ECPA impact analysis. As standardized test methods for non- Apis bees larvae were not available, risk assessment according to EFSA for bumblebees and solitary bees based on the honey bee endpoint as surrogate corrected by a safety factor of 10. Morevoer, the sensitivity of the NOEDs at D8 and D22 in repeated exposure (D 22) studies were analysed. Overall, the toxicity of fungicides and herbicides to honey bee larvae (expressed as means and medians of NOED and LD50 values) was moderate to low, while insecticides as expected displayed stronger toxicity. Moreover, the endpoints for herbicides were on average a factor of 2 higher than fungicides which ranges within the normal biological variability (factor of 3). In addition, it is unclear, if the difference is related to a slightly higher toxicity or other factors like different physical chemical properties (e.g. lower solubility). For insecticides, toxicity was about 125 (based on medians) and 6 to 8 (based on means) times higher than herbicides. In the screening risk assessment according to EFSA Bee GD the majority of fungicide (83.3%) and herbicide (95.6%) uses passed the risk assessment for larvae; whereas, for all insecticide uses thr pass rate was about 29%. In the Tier 1 risk assessment, these pass rates slightly increased and were even higher in the ‘treated crop’ and ‘weed in the field’ scenarios for fungicide and herbicide uses, almost being 100%. Pass rates for insecticide uses did not improve very much and amounted to be about 42% for both scenarios. When basing the risk assessment of bumblebee and solitary bee larvae on 1/10th of the honey bee larval endpoint, the majority of active substances and their respective products will fail the screening (overall about 96%) and Tier 1 risk assessment (overall about 90%). Alternative risk assessment approaches proposed by ECPA (e.g. following the EPPO approach; ECPA Option 1 using refinement options and more representative assumptions) or comparing an assummed exposure concentration to the NOEC (ECPA Option 2) led to a slight increase (Option 1) or even no differences in the pass rates (Option 2a) compared to EFSA Tier 1 risk assessment. Thus both, the standard risk assessment according to the EFSA Bee GD as well as the alternative ECPA Option 1 and 2 result in a clear distinction between products with high toxicity (insecticides) vs. non-toxic products (herbicides and fungicides) for the honey bee risk assessment. The sensitivity analysis of repeated exposure studies according OECD GD 239 indicated that in most cases toxicity did not increase during the pupation period between D8 and D22. Thus, the larval growing period between D3 and D8 represents the most sensitive period of the pre-imaginal development.In addition to other assessments, the EFSA bee guidance document (2013) requires the risk assessment of plant protection products on honey bee larvae. At the time the EFSA GD was finalized, no data on honey bee larvae were available due to absence of suitable methods. That is why in 2013 the European Crop Protection Association (ECPA) perfomed an impact analysis of the new EFSA risk assessment, using extrapolated endpoints derived from acute oral honey bee endpoints. Today, a number of honey bee larvae toxicity studies (138 active substances or formulated products) have been conducted according to the newly developed testing methods for single exposure (OECD TG 237) repeated exposure studies until the end of the larval development (D7/D8) and repeated exposure testing (OECD GD 239) until adult hatch (D22). These experimental data have been used to determine the ‘pass rates’ for 215 worst case uses (72 fungicide spray and solid uses, 91 herbicide spray uses, incl. 8 PGR uses and in total 52 insecticide spray and solid uses, incl. 2 nematicide and 3 IGR uses) according to the EFSA Bee GD and to compare with the original ECPA impact analysis. As standardized test methods for non- Apis bees larvae were not available, risk assessment according to EFSA for bumblebees and solitary bees based on the honey bee endpoint as surrogate corrected by a safety factor of 10. Morevoer, the sensitivity of the NOEDs at D8 and D22 in repeated exposure (D 22) studies were analysed. Overall, the toxicity of fungicides and herbicides to honey bee larvae (expressed as means and medians of NOED and LD50 values) was moderate to low, while insecticides as expected displayed stronger toxicity. Moreover, the endpoints for herbicides were on average a factor of 2 higher than fungicides which ranges within the normal biological variability (factor of 3). In addition, it is unclear, if the difference is related to a slightly higher toxicity or other factors like different physical chemical properties (e.g. lower solubility). For insecticides, toxicity was about 125 (based on medians) and 6 to 8 (based on means) times higher than herbicides. In the screening risk assessment according to EFSA Bee GD the majority of fungicide (83.3%) and herbicide (95.6%) uses passed the risk assessment for larvae; whereas, for all insecticide uses thr pass rate was about 29%. In the Tier 1 risk assessment, these pass rates slightly increased and were even higher in the ‘treated crop’ and ‘weed in the field’ scenarios for fungicide and herbicide uses, almost being 100%. Pass rates for insecticide uses did not improve very much and amounted to be about 42% for both scenarios. When basing the risk assessment of bumblebee and solitary bee larvae on 1/10th of the honey bee larval endpoint, the majority of active substances and their respective products will fail the screening (overall about 96%) and Tier 1 risk assessment (overall about 90%). Alternative risk assessment approaches proposed by ECPA (e.g. following the EPPO approach; ECPA Option 1 using refinement options and more representative assumptions) or comparing an assummed exposure concentration to the NOEC (ECPA Option 2) led to a slight increase (Option 1) or even no differences in the pass rates (Option 2a) compared to EFSA Tier 1 risk assessment. Thus both, the standard risk assessment according to the EFSA Bee GD as well as the alternative ECPA Option 1 and 2 result in a clear distinction between products with high toxicity (insecticides) vs. non-toxic products (herbicides and fungicides) for the honey bee risk assessment. The sensitivity analysis of repeated exposure studies according OECD GD 239 indicated that in most cases toxicity did not increase during the pupation period between D8 and D22. Thus, the larval growing period between D3 and D8 represents the most sensitive period of the pre-imaginal development

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

ISSN:0340-7594ISSN:1432-135