Anders Aak

Wind tunnel behavioural response and field trapping of the blowfly Calliphora vicina.

The attraction of the blowfly Calliphora vicina Robineau‐Desvoidy, 1830 (Diptera: Calliphoridae) to single synthetic compounds, blends and authentic odours was investigated in a wind tunnel. A total of 1850 C. vicina (1750 females and 100 males) were tested. A comparison of male and female responses showed significant differences in attraction between the sexes. Females were more attracted than males to liver odour. The attraction of females lay in the ranges of 0–22% for single compounds, 26–64% for synthetic blends and 58–88% for authentic odours. Dimethyl trisulphide was the most attractive single compound. Significant improvement in attraction was achieved with blends and a three‐component lure, consisting of dimethyl trisulphide, mercaptoethanol and o‐cresol, was found to be the best solution for field trapping of C. vicina. Authentic odours from dead fish and mice were significantly more attractive than liver and the three‐component blend, and the blend and liver were similarly effective as attractants. Field tests support the results of the wind tunnel study and a high number of C. vicina were caught in funnel traps. Overall, 99.1% of the specimens caught were females.

Sex differences in olfaction-mediated visual acuity in blowflies and its consequences for gender-specific trapping

The behaviour of 650 female Calliphora vicina Robineau‐Desvoidy (Diptera: Calliphoridae) was examined in a wind tunnel using odour, in combination with six artificial visual stimuli, ranging from a simple black square to a three‐dimensional model of a dead mouse. The carcasses of laboratory mice were used to provide a natural odour and visual source, and a blend consisting of dimethyl trisulphide, mercaptoethanol, and o‐cresol was used to provide a synthetic lure. Significant differences were found in attraction to these odour sources: 90% of the flies oriented upwind to the natural source and 62% to the synthetic lure. No significant differences were found in upwind orientation towards different visual stimuli, but flies showed significantly more landings if the visual cues provided a vertical contrast against the background. A horizontal contrast gave no difference in landing rate compared to treatments without visual cues. In a field study, the blowfly genera Pollenia, Calliphora, and Lucilia were caught. The overall blowfly catch was significantly higher when an odour lure was present (Pollenia: 3×, Calliphora: 15×, Lucilia: >79×). A significant three‐way interaction between visual cue, genus, and gender was found. The saprophagous Lucilia and Calliphora showed a gender‐specific response to visual stimuli, whereas the parasitic Pollenia did not. A 2:1 female:male sex ratio was found for Calliphora spp. and a 12:1 sex ratio for Lucilia spp. The data suggest that landing responses of male and female saprophagous blowflies, and consequently trap catches, result from olfaction, but also from gender‐specific visual responses when under the influence of odour.

Bed bugs, their blood sources and life history parameters: a comparison of artificial and natural feeding

A blood‐feeding system that utilizes a small amount of whole heparinized human blood in parafilm bags is described in detail, and similarities and differences between artificially fed and naturally rodent‐fed bed bugs (Hemiptera: Cimicidae) are discussed. Blood with high levels of heparin (10%) was unsuitable for artificial colony rearing, whereas bed bugs fed on 1% heparinized blood and those that naturally ingested rat blood completed their lifecycle with similar stage structures over time, with no significant differences in mortality. No differences in feeding efficiency or fertility were found in a direct comparison of bed bugs maintained under each of these two treatments, but analysis of the full lifecycle revealed that artificially fed bed bugs became significantly smaller and laid fewer eggs than rodent‐fed bed bugs. The level of membrane stretching regulated the number of bed bugs that fed. When the membrane was stretched to twice its length and width, 96% of bed bugs successfully fed through the parafilm. Whole heparinized blood that was stored at 6 °C for ≥ 14 days failed to retain its nutritional value and the amount of blood consumed and number of consecutive moults were significantly reduced.

Blowfly (Diptera, Calliphoridae) damage on stockfish in northern Norway: pest species, damage assessment and the potential of mass trapping

Production of high quality stockfish in northern Norway takes place from February to May. The dominant blowfly species (Diptera: Calliphoridae) with adults present during stockfish production were Calliphora vicina and Protophormia terraenovae. Larval collections identified the damage-causing species to be C. vicina. Other saprophagous blowfly species were only found after the production period. Fish dried in sun-exposed locations experienced more damage than fish in shaded locations, and the risk of damage was higher in fish dried later in the production period. Yellow sticky traps and funnel traps baited with dimethyl trisulphide were tested for their potential in mass trapping. Sticky traps caught flies during early spring, while funnel traps increased in efficiency closer to summer. Attraction to dimethyl trisulphide was found to be significantly higher for C. vicina compared to P. terraenovae, and the catch of C. vicina consisted of 92% females. The catch of female flies during the critical drying period consisted of 5–30% of the estimated number of flies having caused damage. The target specificity with high female catches and the cost efficiency of these traps indicate that mass trapping can be used as an integrated part of a management program to reduce damage from blowflies in stockfish producing areas.

Questing activity in bed bug populations: male and female responses to host signals.

A large‐arena bioassay is used to examine sex differences in spatiotemporal patterns of bed bug Cimex lectularius L. behavioural responses to either a human host or CO2 gas. After release in the centre of the arena, 90% of newly‐fed bed bugs move to hiding places in the corners within 24 h. They require 3 days to settle down completely in the arena, with generally low activity levels and the absence of responses to human stimuli for 5 days. After 8–9 days, persistent responses can be recorded. Sex differences are observed, in which females are more active during establishment, respond faster after feeding, expose themselves more than males during the daytime, and respond more strongly to the host signal. The number of bed bugs that rest in harbourages is found to vary significantly according to light setting and sex. Both sexes stay inside harbourages more in daylight compared with night, and males hide more than females during the daytime but not during the night. The spatial distribution of the bed bugs is also found to change with the presence of CO2, and peak aggregation around the odour source is observed after 24 min. Both male and female bed bugs move from hiding places or the border of the arena toward the centre where CO2 is released. Peak responses are always highest during the night. Bed bug behaviour and behaviour‐regulating features are discussed in the context of control methods.

Phenology and life history of the blowfly Calliphora vicina in stockfish production areas

Calliphora vicina Robineau‐Desvoidy (Diptera: Calliphoridae) causes yearly losses of 1–2 million Euros to the stockfish industry in Lofoten, Norway. To develop an efficient management program, knowledge of its life cycle and phenology in production areas is needed. Cohort studies in a simulated Lofoten climate showed that field abundance peaks of adults in early spring and midsummer can be explained by a cohort originating from stockfish and its subsequent generations. Laboratory simulations with normal, increased, and decreased Lofoten temperatures indicate that C. vicina overwinter as a mix of larvae, pupae, and adults, and a temperature change of ± 2 °C significantly influences reproductive timing, reproductive output, and female mortality. Flies originating from stockfish reproduced during the first summer when temperatures were increased 2 °C above normal. At lower temperatures, the reproductive investment was low or absent during the first summer and the adult flies entered the winter in a diapausing state. Most offspring produced during the first summer and autumn developed continuously without maternally induced diapause, pupated during the winter, and hatched in the early spring to co‐occur with their parent generation during stockfish production. Calliphora vicina showed flexibility in reproductive efforts and overwintering strategies. The high proportion of adults overwintering compared with the commonly used larval diapause strategy might be interpreted as an adaptation to exploit the stockfish resource. The majority of female C. vicina that cause damage to stockfish likely developed on fish dried the previous year, and a continuous year‐long trapping is recommended to decimate the population.

Mortality, temporary sterilization, and maternal effects of sublethal heat in bed bugs.

Adult bed bugs were exposed to the sublethal temperatures 34.0°C, 35.5°C, 37.0°C, 38.5°C, or 40.0°C for 3, 6, or 9 days. The two uppermost temperatures induced 100% mortality within 9 and 2 days, respectively, whereas 34.0°C had no observable effect. The intermediate temperatures interacted with time to induce a limited level of mortality but had distinct effects on fecundity, reflected by decreases in the number of eggs produced and hatching success. Adult fecundity remained low for up to 40 days after heat exposure, and the time until fertility was restored correlated with the temperature-sum experienced during heat exposure. Three or 6 days of parental exposure to 38.5°C significantly lowered their offspring’s feeding and moulting ability, which consequently led to a failure to continue beyond the third instar. Eggs that were deposited at 22.0°C before being exposed to 37.0°C for 3 or 6 days died, whereas eggs that were exposed to lower temperatures were not significantly affected. Eggs that were deposited during heat treatment exhibited high levels of mortality also at 34.0°C and 35.5°C. The observed negative effects of temperatures between 34.0°C and 40.0°C may be utilized in pest management, and sublethal temperature exposure ought to be further investigated as an additional tool to decimate or potentially eradicate bed bug populations. The effect of parental heat exposure on progeny demonstrates the importance of including maternal considerations when studying bed bug environmental stress reactions.

Blow fly responses to semiochemicals produced by decaying carcasses.

Volatiles from mouse carcasses in decay stages ranging from fresh to 33 days old were used to investigate oriented flight and landings in male and female blow flies of Calliphora vicina Robineau‐Desvoidy (Diptera: Calliphoridae). Oriented flight increased significantly from 36% towards fresh carcasses to 68%, 61% and 65% towards carcasses aged 3 days, 6 days and 9 days, respectively. Carcasses aged 20 days and 33 days were significantly less attractive, achieving 51% and 41% attraction, respectively. No differences emerged between the sexes in oriented flight, but a significant increase in female landings at the most attractive carcasses was observed. Headspace collections from the different stages of decay showed a succession in the volatile profile emitted from the carcasses and identified nine chemicals which peak in quantity in concurrence with the most attractive stages of decay. Three of these chemicals also showed dose–response effects as indicated by a significant correlation between the amount present and the proportion of flies responding. Blow flies are important pests and efficient traps are needed. The significant interaction between fly sex and carcass age highlights behavioural differences between male and female blow flies which can be exploited in blow fly trapping. Three new volatile chemicals, butylated hydroxyl toluene, 3‐hydroxy‐2‐butanone and nonanal, emitted from dead mice are suggested as potential attractants.

Mortality, fecundity and development among bed bugs (Cimex lectularius) exposed to prolonged, intermediate cold stress

Abstract BACKGROUND Bed bugs (Cimex lectularius L.) have returned as a nuisance pest worldwide. Their ability to withstand different types of environmental stress should be explored in order potentially to increase the efficiency of control methods. RESULTS Immediate and long‐term effects of exposure to temperatures from 0 to −10 °C for 1, 2 and 3 weeks are reported. Fifth‐instar nymphs and adults were exposed to constant or fluctuating temperatures. Increased cold and extended time yielded higher mortality; nymphs were more resilient than adults at the shorter durations of exposure. At intermediate temperatures, mortality was higher at constant compared with fluctuating temperatures, whereas all individuals died after 3 weeks of exposure to −7 °C. The success among survivors after cold treatment was also affected in terms of reduced egg production, hatching success and the ability of fifth‐instar nymphs to advance into the adult stage; however, nymphs produced after cold treatment developed normally. CONCLUSIONS Detrimental effects of prolonged exposure to low temperatures were seen in bed bugs both during and after cold treatment. The results suggest that temperatures below −7 °C can be applied by laymen to control this pest in small items if available treatment time is of less concern.

Mortality, fecundity and development amongbed bugs (Cimex lectularius) exposed toprolonged, intermediate cold stress

Abstract BACKGROUND Bed bugs (Cimex lectularius L.) have returned as a nuisance pest worldwide. Their ability to withstand different types of environmental stress should be explored in order potentially to increase the efficiency of control methods. RESULTS Immediate and long‐term effects of exposure to temperatures from 0 to −10 °C for 1, 2 and 3 weeks are reported. Fifth‐instar nymphs and adults were exposed to constant or fluctuating temperatures. Increased cold and extended time yielded higher mortality; nymphs were more resilient than adults at the shorter durations of exposure. At intermediate temperatures, mortality was higher at constant compared with fluctuating temperatures, whereas all individuals died after 3 weeks of exposure to −7 °C. The success among survivors after cold treatment was also affected in terms of reduced egg production, hatching success and the ability of fifth‐instar nymphs to advance into the adult stage; however, nymphs produced after cold treatment developed normally. CONCLUSIONS Detrimental effects of prolonged exposure to low temperatures were seen in bed bugs both during and after cold treatment. The results suggest that temperatures below −7 °C can be applied by laymen to control this pest in small items if available treatment time is of less concern.