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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. [ABSTRACT FROM AUTHOR]

Certain ichneumonid parasitoids (Hymenoptera) use self-produced vibrations transmitted on plant substrate, so-called vibrational sounding, to locate their immobile concealed pupal hosts. An ambient temperature dependency with higher frequencies and intensities at higher temperatures is postulated because signals are of myogenic origin. Here, temperature influence on vibratory signals is analysed in the temperate parasitoid Pimpla turionellae under different thermal conditions using plant-stem models to elicit host-searching behaviour. Signals are measured with laser Doppler vibrometry and analysed for time parameters and frequency components applying fast-Fourier transformations. The results reveal an unexpected effect of ambient temperature on signals produced by the female wasps. Although average values of time parameters (pulse trains, pulse train periods, inter pulse duration) are unchanged by ambient temperature, the frequency parameters show an inverse thermal effect. Within the temperature range tested (8–26 °C), decreasing temperature leads to significantly higher frequency and intensity of the self-produced vibrations in the temperate species. This inverse thermal effect may be explained by a temperature-coupled signal production in the frequency domain to compensate negative low-temperature effects on the mechanoreceptors by increased muscle activity. The option of heterothermy to produce signals reliably during vibrational sounding under low temperature is also discussed. [ABSTRACT FROM AUTHOR]

Several parasitic wasps of the Pimplinae (Ichneumonidae) use self-produced vibrations transmitted through plant substrate to locate their concealed immobile hosts (lepidopteran pupae) by reflected signals. This mechanosensory mechanism of host location, called vibrational sounding, depends on the physical characteristics of the plant substrate and the wasp’s body and is postulated to depend on ambient temperature. Adaptations of two parasitoid species to thermal conditions of their habitats and the influence of temperature on the trophic interaction during host location are investigated in the tropical Xanthopimpla stemmator (Thunberg) and compared with the temperate Pimpla turionellae (L.). Plant-stem models with hidden host mimics are offered to individual wasps under defined temperature treatments and scored for the number and location of ovipositor insertions. Significant effects of temperature are found on host-location activity and its success. The tropical species possesses an optimum temperature range for vibrational sounding between 26 and 32 °C, whereas the performance decreases both at low and high temperatures. The temperate species reveals substantial differences with respect to performance at the same thermal conditions. With increasing temperature, P. turionellae shows a reduced response to the host mimic, reduced numbers of ovipositor insertions, and decreased precision of mechanosensory host location. In the tropical X. stemmator, the female wasps are able to locate their host with high precision over a broad range of ambient temperatures, which suggests endothermic thermoregulation during vibrational sounding. Environmental physiology may therefore play a key role in adaptation of the host location mechanism to climatic conditions of the species’ origin. [ABSTRACT FROM AUTHOR]

Plant architecture of apple trees in commercial orchards was rapidly changed from traditional tall trees to dwarf trees to optimize yield and fruit quality. Additionally, hail nets are widely used to prevent yield loss by hail. These changes are expected to considerably influence the orchard microclimate and thus the developmental rates of pest insects in apple. However, these relationships have not yet been fully elucidated. The present study was conducted over the seasonal cycle to investigate the influence of plant architecture and hail nets on the habitat temperatures of the codling moth, Cydia pomonella (L.) (Lepidoptera: Tortricidae), in apple, Malus domestica Borkh. (Rosaceae). Within the canopies, leaf area index (LAI) and global site factor (GSF) were quantified using hemispherical photography. Temperature was analysed for the main habitats of the different codling moth stages, i.e., air within the canopy, bark of tree stems, and apple fruit. In dwarf trees, LAI was lower, leading to a higher GSF than in tall trees. Hail nets did not influence LAI and GSF. Results for dwarf trees compare as follows with those for tall trees: Average air temperatures within the canopy were 0.7 °C higher during daytime, whereas 0.4 °C lower at night. Mean surface temperatures of bark were 0.9 °C higher on sunny and 0.4 °C on overcast days. Mean surface temperatures of apple fruits were 1.8–2.7 °C higher on sunny days, but 0.6 °C cooler on overcast days. The effect of hail nets was confined to a reduction of the air temperature within the canopy by approximately 0.2–0.8 °C. Bark and apple surface temperatures were not significantly affected. Based on the temperature differences in the habitats considered, the calculated development of the codling moth in dwarf trees was on average 3 days faster than in tall trees. The calculations imply a negligible effect of hail nets on codling moth development. [ABSTRACT FROM AUTHOR]

The thermoregulation behaviour of the adult codling moth, Cydia pomonella, is investigated in the laboratory using temperature gradient experiments. Unmated males and females are tested at dawn when moths typically move to resting sites. Mated females are tested during oviposition over a complete diurnal cycle. Temperature strongly affects microhabitat selection in adult moths. Unmated males and females prefer to rest at the low-temperature ends of temperature gradients between 15 and 32 °C. Relative humidity does not influence the thermal response in unmated females, whereas males show a less distinct temperature selection under high humidity. By contrast to unmated moths, ovipositing females prove to be highly thermophilous (i.e. they deposit the highest proportions of their eggs in the zones of highest temperatures of gradients between 15 and 36 °C). This striking discrepancy in thermal response of females between their premating and oviposition period is likely to reflect an adaptation to different selection pressures from the thermal environment. Unmated moths may benefit from low temperatures by a longer lifespan and crypsis within the tree canopy, whereas the choice of warmer oviposition sites by mated females will favour a faster development of eggs. [ABSTRACT FROM AUTHOR]

The selection of habitats with favourable temperature by the apple blossom weevilAnthonomus pomorum(L.) is investigated in a temperature gradient arena with a range of approximately 0–15 °C. Single female and male weevils are tested in the arena 2, 4 and 6 days after termination of diapause, during photophase and during scotophase. During photophase, weevils of both sexes choose the warmest part of the temperature gradient arena, irrespective of the time elapsed after diapause. During scotophase, high temperature is favoured by male weevils, as well as by females 2 and 4 days after diapause. However, 6 days after termination of diapause, females show no thermal preference in the temperature gradient arena during scotophase, indicating that thermal choice of femaleA. pomorumin the scotophase changes with time after the termination of diapause. The results suggest that both sexes benefit from thermoregulation by habitat choice during photophase when the weevils are flight active and colonize apple trees. [ABSTRACT FROM AUTHOR]

The thermoregulation behaviour of the codling moth,Cydia pomonella, is investigated in temperature gradient experiments with larvae feeding within apples, and with mature larvae searching for cocooning sites. Feeding larvae appear to prefer the apple hemisphere with a higher temperature (i.e. they build larger cavities in the radiated, warmer part of the fruit). The proportion of larval cavities in the warmer hemisphere is positively related to increasing apple temperature on that side, as well as to the temperature difference between the warm and the cool fruit hemisphere. The mechanism in feeding larvae can be termed as cryptic basking because, during microhabitat selection, the caterpillars exploit temperature differences that are caused explicitly by incident solar radiation. Fifth-instar larvae in search of cocooning sites show no temperature preference within the large gradient offered (9–29 °C), with no difference between males and females. During larval development, the insect changes its thermoregulation behaviour in response to a possible shift in benefits of an elevated body temperature with respect to environmental conditions. Both the thermoregulation behaviour and such a shift of behavioural response should be respected when simulating body temperatures of the species. [ABSTRACT FROM AUTHOR]

The significance of the apple blossom weevil, Anthonomus pomorum L. (Coleoptera: Curculionidae), as a potential threat to apple, Malus domestica Borkh., has increased over the past two decades in many regions of Europe. The apple blossom weevil immigrates into orchards and colonises apple trees in early spring. Females deposit single eggs into closed blossom buds, which leads to capped blossoms. This study was designed to test the suitability of transparent shelter traps for the surveillance of colonisation under different population pressures, and to assess the quantitative relationship between number of weevils caught and: (1) absolute injury, expressed as number of infested buds, as well as (2) relative injury, expressed as a percentage of infested buds relative to all buds on the tree. The findings with the new shelter traps were contrasted to results from limb jarring. Numbers of weevils caught with the transparent shelter trap were positively correlated with absolute injury, as well as with relative injury across the five study sites, whereas weevil counts with limb jarring were not correlated with absolute injury, but only with relative injury. Our data validate the transparent shelter trap as a method for accurately monitoring the course of spring colonisation of A. pomorum and demonstrate its potential for predicting injury by the weevils to blossom buds. In contrast, the significance of limb jarring for monitoring both the time course of colonisation and subsequent injury is limited. The significant linear relationship between the number of weevils caught in shelter traps and the relative injury allows for predictions of potential damage before oviposition takes place, i.e., early enough for an insecticide application where necessary. [ABSTRACT FROM AUTHOR]

Investigates the response of Pimpla turionellae towards plant stem models with shades of gray on a white substrate. Demonstration that the absolute amount of achromatic contrast is the critical parameter for visual host location; Increased ovipositor insertion activity due to increased contrast.

Based on the model system of Brussels sprouts [ Brassica oleracea var. gemmifera (Brassicaceae)], the herbivore cabbage white caterpillar, Pieris brassicae (L.) (Lepidoptera: Pieridae), and the parasitoid wasp, Cotesia glomerata (L.) (Hymenoptera: Braconidae), the influence of plant damage type, and damage duration were assessed on plant volatile emission and subsequent recruitment of natural antagonists of the herbivore. Plants were damaged by three methods for a period of either 3 or 8 h: herbivore damage (HD), progressive mechanical damage, and final mechanical damage inflicted in a single event. Wind-tunnel bioassays evaluated whether the mode of damage affected female parasitoid oriented flight. After both periods of damage, all treatments were highly significantly preferred by naïve C. glomerata to undamaged control plants. After 3 h, herbivore-damaged plants were significantly preferred to plants with final damage (FD). Most remarkably, following 8-h damage, the parasitoid preferred both herbivore-damaged and progressively damaged plants to plants with FD and did not significantly discriminate between herbivore and progressively damaged plants, thus indicating a similarity in plant response to herbivore and progressive mechanical damage. In addition to wind-tunnel bioassays, emitted plant volatiles were collected and analysed by thermal desorption gas chromatography/mass spectrometry, following 3 and 8 h of damage in order to correlate volatiles released from different damage types with the attraction of the parasitoid. Differences in volatile profiles from all damage types were similar following both 3 and 8 h of damage, with only ( Z)-3-hexenyl acetate found to be emitted in significantly higher quantities by final mechanical damage compared with HD after 3 h. In conclusion, the plant's response to progressive mechanical damage was more similar to HD than final mechanical damage deployed at a single point in time, irrespective of damage duration, and C. glomerata did not significantly discriminate between progressive damage and HD. [ABSTRACT FROM AUTHOR]

The walnut husk fly, Rhagoletis completa Cresson (Diptera: Tephritidae), has recently invaded Switzerland, Austria, Germany, and France, probably crossing the alpine divide after its initial introduction into Italy. Here, the susceptibility of 36 walnut [ Juglans regia L. (Juglandaceae)] cultivars to attack by R. completa was studied in an experimental orchard in Switzerland. Walnut cultivars differed significantly in infestation rates; cultivars that produced large, heavy fruit harboured significantly more larvae than cultivars that produced smaller fruit. Pupal weight was significantly influenced by cultivar, but not by any of the physical properties that we measured. For individual fruit within a cultivar, pupal weight was weakly related to fruit weight and infestation level. Adult longevity was correlated with pupal weight and appeared to be favoured in flies that developed in large-fruit cultivars. The longevities of adults recovered from different cultivars differed significantly. The shortest longevity was recorded for flies recovered from Geisenheim 1049 (39.2 ± 2.80 days) and the longest for flies recovered from Sheinovo (68.8 ± 21.75 days). Differences in diapause length were also highly significant and varied between 167 ± 5.1 (Esterhazy III) and 257.4 ± 8.21 days (Mayette). These results suggest that (1) across and within cultivars, walnut husk flies prefer to infest (i.e., they develop better in) large, heavy fruit, and (2) offspring that develop in large fruit are likely to accrue fitness advantages over the offspring of females using smaller fruit. Our results provide the basis for subsequent studies on resource defence by males, as they enable a prediction of which type of fruit males should defend more vigorously. [ABSTRACT FROM AUTHOR]