The Entomologist's record and journal of variation . One curve (•-•) assumes no flight speed for theinsect (and can also be interpreted as a random orientation coupledwith a constant flight speed of any magnitude). The second curve(x-x) assumes a ten knot downwind insect flight component addedto the ambient wind. The steplength between adjacent symbols onany one curve is three hours to 0000 hours on 1st April and sixhours to the end of the curve. At the midnight points, the twocurves are connected by a dotted line for any given date. The backtrack for the second livomica is shown in Figure
The Entomologist's record and journal of variation . One curve (•-•) assumes no flight speed for theinsect (and can also be interpreted as a random orientation coupledwith a constant flight speed of any magnitude). The second curve(x-x) assumes a ten knot downwind insect flight component addedto the ambient wind. The steplength between adjacent symbols onany one curve is three hours to 0000 hours on 1st April and sixhours to the end of the curve. At the midnight points, the twocurves are connected by a dotted line for any given date. The backtrack for the second livomica is shown in Figure constraints imposed upon the two curves are identical to thosedescribed for Figure 1. The capture time was 0300 hours on 17thApril, and the steplength is three hours for the whole should be noted that this method of backtracking can only beused to provide a general indication of the nature of any immigration. *The Dell, Stallaids Lane, Tilford Road, Rushmoor, Fainham, Surrey. 166 ENTOMOLOGISTS RECORD, VOL. 97 f^ tx^. Figure 1. Backtrack for livornica taken at 2100 hours on 2/4/1985 nearHaslemere. In this analysis the following conditions were assumed: a) insect orientation and flight speed were as described above. b) continuous fliglit of the insect for a minimum of 90 hoursprior to capture. c) flight at sea level throughout. From Figure 1 it appears that a likely source may have been theCanary Isles and/or that part of Africa adjacent to the Canaries. Theweather in the area at that time was unusually warm, with lightwinds from the Sahara. (Midday temperatures in Tenerife between30th March and 2nd April were 270C, some 70C above the earlyApril norm). It is interesting that the ten knot curve (x—x) passesquite close to north-west Iberia, and both curves pass over 2 is less easy to interpret, with no indication of any low lati-tude source. A number of possible explanations can be advanced: a) the insect was resident in the area of
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