Aphids, ants and pheromones

5-39 Nature Vol. 262 August 12 1976 cussion rather academic but democracy being what it is a firm decision by Britain's 17 % could sway the day. Four major missions were discussed, the Space Telescope clearly winning the day and being regarded as an instrument of outstanding and paramount importance. It is hoped that the telescope will appear in NASA's 1978 budget although it has already slipped considerably in time and in size, the main mirror now being 2.4 m in apertme. From its 500-600 km high orbit it will be able to detect objects 100 t:imes fainter that those detectable from the Earth's surfoce (it will be able to pick up 29th magnitude stars) and will have an angular resolution better than 0.1 arc s, some 10 times better than attainable from the ground. Coupled with this diffraotion-limited performance is the fact that being free from atmospheric absorption it will have a speotral range of 912 A to 1 mm. Within our Galaxy it will study the early and late stages of stellar evolution, the position and proper motion of stars, the dust distribution and hydrogen concentration and also our Solar System. Extragalactic work will include investigations of the structure, scale and evolution of the Universe, the structure and content of galaxies and also quasars. It is obviously a project that no astronomical nation wants to be lef:t out of. NASA and the US Congress look :to ESA ,to contribute more than 10 % of the cost in return for an equal percentage of the observing time and an involvement in directing ,the project. This 10% of the cost would be spent in Europe, designing, developing and constructing some of the instrumenta,tion and the technology (for example the faint object camera and the solar arrays). This cooperation would of course mop up a considemble amount of ESA's science budget for a few years and, while recognising the great importance of the projec,t, some of the scientists present at the meeting pointed out tha:t science per se would not suffer if we did not participa,te, the Americans proba:bly going on by themselves, whereas spending the money on specifically European ideas might open up new horizons in different fields. The second mission considered was again a cooperation wth NASA and involved rtwo spacecraf:t launched simultaneously towards Jupiter from a space shuttle, and then guided in such a way ,that one would be deflected by Jupiter towards the no11th pole of the Sun, the other passing over the south pole. ESA would supply one spacecraft and NASA would use a Pionee,r type spacecraft for the other. This "out of ecliptic" mission would provide a new insight dnto interplanetary and solar physics and the science of the Jovian magnetosphere, mainly by taking the Aphids, ants and pheromones from our Insect Physiology Correspondent IT was shown by J. S. Edwards many (Science, 192, 1349; 1976) have now years ago that ,the secre,tion from the studied rthe response ,to these pherocornicles of aphids consists oif oily drop- mones in ,the ants which herd certain lets, now known to be a mixture of aphid species. These myrmecophilous ,triglyce,rides, in aqueous suspension. On aphids enjoying, as they do, protection release ,in contact wHh a solid surface by their ants from predators, are much this secretion quickly crystallises to less responsive to ,the alarm pheroform a hard waxy plaque. It thus pro- mones than nonamyrmecophilous spevides a mechanical protection against cies. They may walk away on exposure to ,the alarm pheromone, but they do small predators and parasites. In recent years ,the cornides have not drop off the feeding site. At the been found to liberate also alarm same time, and not su11prisingly, the pheromones, which are secreted in res- ants themselves respond to aphid alarm ponse ,to predators and parasites. pheromones. In experimental trials it Bowers et al. (Science, 177, 1121; appeared that the ants were prepared 1972), isolated and identified trans-/3- to stroke with their antennae any aphid farnesene (TBF) as the alarm phero- spooies they were offered; but ,the difmone in several aphid species; this ferent aphid species vary widely in the secretion seems also ,to repel other readiness with which ,they excrete aphids encroaching on occupied feed- droplets of honeydew for ,their ant ing sites. As with ,the alarm phero- keepers. Some species wHI not respond mones of many inseots, TBF is inter- at all. The Macrosiphini were caused specific: it is present in all species to disperse by the ants' stroking: this examined in the subfamily Aphidinae, provoked a predatory response by ,the and all of them (with ,the exception of ants, and ,the aphids were carried off to the turnip aphid Hisdaphis) show the nest and presumably eaten. alarm activity to pure synthetic TBF. The acceptance of ,the attentions of But other unidentified alarm phero- ants replaces response to alarm pheromones are present in addition to TBF mones: the myrmecophi!ous aphids and these different blends of phero- rely on their ants for protection. mone probably account for the dif- Indeed, artificial liberation of TBF ferent responses :in different aphid leads ,to attack by the ants, not on the species. Thus ,the turnip aphid which aphids but on any suspected predators fails to react to TBF, secretes this by which they appear to be attacked. pheromone in its cornicle fluid, and it The threshold of ,response to the reac,ts to ,the secretions of other aphid pheromone by the ant is, indeed, even lower ,than the threshold in the aphids species. Nault, Montgomery and Bowers themselves. observer away from the plane of the planetary orbits where the large majority of observations have been made ,to date. The two satellites would obtain a stereoscopic view of the Sun and help ,to test ,the fundamental symmetry of the Solar System. The basic experiments would consist of a magnetomete,r, a plasma probe, a solar particle ,telescope, a cosmic ray telescope, a receiver for studying radio propagation, a coronag.raph and a XUV heliograph. The 85° inclination of the OI'bits to the ecliptic will enable the development of equa,torial st,ructures on the Sun to be followed oontinuously through several solar rotations. Thre,e other projects are ,to be studied further. LIRTS, a 2-3 metre classical, uncooled Cassegrain infrared telescope on Spacelab would provide high sensitivity photometry with high spatial resolution enabling many astronomical objeots to be studied thmugh the measurement of a,tomic and molecular lines in ,the far infrared. EXPOS again uses Spacelab to fly a © 1976 Nature Publishing Group set of instruments to study the spectra of cosmic X-ray sources and ,to deteot polarised X-ray emission. The payload comprises a number of large area B,ragg spectrometers each selected to study particular features in ,the 0.5 to 10 keV •range. Spatial resolution of about 1 arc min and energy resolution of 10 to 20% at 1 keV is obtained by using an X-ray grating with a large area Walter I (...truncated)