Research Letter #10

WHERE THERE’S SMOKE ...

... THERE’S A BIOLOGICAL TRICK OR TWO

We have already seen that smoke consists of a wide range of chemicals - solid, liquid and gas. It may not be surprising then that smoke can perform some marvelous biological ‘tricks’ when it impinges on the lives of plants and animals. This letter is about a small bag of these tricks.

We see smoke because of its particulate matter. Other animals probably see it similarly. Thus, smoke columns appear to be an indicator to some birds that feeding opportunities are at their source. Black Kites in particular may travel long distances to feed on insects - like cockroaches and grasshoppers - being ‘driven’ along by the fire front. This happens every year in northern Australia. It has been beautifully illustrated in an article in Australian Natural History (Braithwaite and Estbergs 1987-88). An apparent oddity is that some Australian flies are attracted to smoke (Bickel 1996).

Perhaps everybody knows that European bees are subdued by smoke in commercial hives. It is an everyday practice of beekeepers. Smoking the hives takes the sting out of beekeeping! What is the active ingredient of smoke that calms the bees? This appears not to be known but it is thought that smoke interferes with the ability of the bees to smell (Visscher et al. 1995). Anaesthesia in bees, induced by smoke from burning hair, is apparently due to hydrogen sulphide (rotten-egg gas) (Wood 1983).

Strange as it may seem, smoke has been used to stimulate pineapples to flower. Way back in 1932 it was found that the active ingredient in the smoke was a chemical called ethylene (Bartholomew and Kadzimin 1977). It seems reasonable that the fire-stimulated flowering observed in other monocotyledons, like grasstrees (Xanthorrhoea spp.), might be due to the same cause. There is some evidence that this is so (Gill and Ingwersen 1976). For the South African Fire Lily, Cyrtanthus ventricosus - another monocotyledon - smoke stimulated the bulbs to flower but ethylene application failed to do so (see Brown and van Staden 1997).

In recent years, there has been considerable excitement in scientific and horticultural circles in the discovery that smoke stimulates the germination of a range of species (see Brown and van Staden 1997). Many Australian species, previously difficult to germinate, are now readily germinated using smoke or aqueous extracts of smoke (Dixon et al. 1995). Nitrogen dioxide has been implicated as the trigger for the germination of some North American species (Keeley and Fotheringham 1998).

Smoke effects on living systems may be due to particulates, carbon dioxide, ethylene, nitrogen dioxide and probably many other substances. It is a complex and interesting substance. Who knows what other ‘tricks’ it has to reveal?

Literature

Bartholomew, D.P. and Kadzimin, S.B. (1977). Pineapple. In: P. de T. Alvim and T.T. Kozlowski (eds) Ecophysiology of Tropical Crops. Pp. 113-157. Academic Press, New York.

Bickel, D.J. (1996). Smoke flies (Diptera: Platypezidae) and the Sydney bushfires. Australian Entomologist 23, 77-78.

Braithwaite, R. and Estbergs, J. (1987-88). Fire-birds of the Top End. Australian Natural History 22(7), 299-302.

Brown, N.A.C. and van Staden, J. (1997). Smoke as a germination cue: a review. Plant Growth Regulation 22, 115-124.

Dixon, K. W., Roche, S. and Pate, J.S. (1995). The promotive effect of smoke derived from native burnt native vegetation on seed germination of Western Australian plants. Oecologia 101, 185-192.

Gill, A.M. and Ingwersen, F. (1976). Growth of Xanthorrhoea australis R. Br. in relation to fire. J. Appl. Ecol. l3, 195-203.

Keeley, J.E. and Fotheringham, C.J. (1998). Smoke-induced seed germination in California chaparral. Ecology 79, 2320-2336.

Visscher, P.K., Vetter, R.S. and Robinson, G.E. (1995). Alarm pheromone perception in honey bees is decreased by smoke. J. Insect Behavior 8, 11-18.

Wood, W.F. (1983). Anaesthesia of honey bees by smoke from the pyrolysis of puffballs and keratin. J. Apicultural Res. 22, 107-110.

Malcolm Gill
25 March 1999