Dispersion of carbon dioxide plumes in African woodland: implications for host‐finding by tsetse flies

Abstract

Abstract. In Zimbabwe, high‐resolution (10 Hz to an accuracy of ± 0.1 p.p.m.) measurements were made of atmospheric and host‐produced CO2 in tsetse habitats during the dry season. The diel structure of atmospheric CO2 concentrations is bimodal, with a minimum at approximately 16.00 hours and maxima at approximately 05.00 hours and 20.00 hours, respectively. The background CO2 noise is greater in densely vegetated riverine woodland than in leafless, deciduous (mopane) woodland. Variation in atmospheric CO2 concentrations is correlated with decreasing wind speed and increasing thermal stability. Consequently, the background noise during the day is greatest in riverine woodland during early morning and late afternoon, when winds are typically light and stable, and thermal inversion conditions are developing. Measurements were made of CO2 at 8–64 m downwind from natural (two cattle) or synthetic sources (4–20 L min−1 CO2). The signal from the sources appears as fluctuations above threshold (approximately 355–362 p.p.m.), in the form of intermittent ‘bursts’ of CO2. The strength, duration and intermittency of the signals attributable to these sources declines with source strength and distance from the source. In riverine woodland, approximately 50% of all bursts are 0.1 s long, and 10% are > 2.0 s long. Carbon dioxide signals from equivalent sources are stronger in riverine woodland than mopane. Carbon dioxide dispensed at rates of 4–20 L min−1 is detected up to 64 m downwind of the source but peaks are typically < 10 p.p.m. above threshold. Consequently, host‐CO2 signals are obscured during periods of large fluctuations in atmospheric CO2. These results suggest that CO2 is detectable, at least in some circumstances, at tens of metres downwind and hence dispels the notion that its action is limited to that of a short‐range attractant.

Behavioral responses of Drosophila to biogenic levels of carbon dioxide depend on life-stage, sex and olfactory context

“…In natural microhabitats they can reach levels above 0.1% due to respiration of plants, animals and microorganisms (Gillies, 1980;Anderson and Ultsch, 1987;Zollner et al, 2004). We demonstrate here that CO 2 emission from bananas can raise concentrations in the air and that the ripening process leads to a drop in emission with time.…”

“…Carbon dioxide (CO 2 ) is present in the atmosphere at 0.03%, a concentration that can fluctuate considerably with time of day and between different habitats (Gillies, 1980;Zollner et al, 2004). In vertebrates, CO 2 regulates breathing: it is detected by chemoreceptors in the blood stream and in the brain stem (Lahiri and Forster, 2003).…”

Olfaction in vector-host interactions

“…Thus, it was argued that host carbon dioxide could not play a role in long range responses and activation -behavioural responses which are likely to occur up to 90 m downwind of the host. However, detection of carbon dioxide is not necessarily limited by its presence in the atmosphere but rather, its variability (Zollner et al 2004). Using high performance (10 Hz to an accuracy of ±0.1 ppm) infra-red carbon dioxide analysers, Zollner et al (2004) showed that carbon dioxide released 4-20 l/min can be detected up to 64 m downwind.…”

“…However, detection of carbon dioxide is not necessarily limited by its presence in the atmosphere but rather, its variability (Zollner et al 2004). Using high performance (10 Hz to an accuracy of ±0.1 ppm) infra-red carbon dioxide analysers, Zollner et al (2004) showed that carbon dioxide released 4-20 l/min can be detected up to 64 m downwind. The resolution and sensitivity of the instruments are comparable to those of an insect, suggesting that, in principle, carbon dioxide is detectable by insects at long range.…”

Impact of elevated CO2 background levels on the host-seeking behaviour of Aedes aegypti

“…when flying mosquitoes are exposed to intermittent increases in CO 2 concentration above background, as shown under controlled conditions (Geier et al, 1999;Dekker et al, 2001). Such a plume is encountered naturally by mosquitoes up to tens of metres from a host (Costantini et al, 1996;Zöllner et al, 2004). However, in a variable ambient CO 2 background, the effective range of attraction could decrease, due to limitations of the CO 2 chemosensory system.…”