Size and fecundity in the Jamaican gall-midge Asphondylia boerhaaviae

ABSTRACT. 1. The gall-midge Asphondylia boerhaaviae Möhn galls weeds belonging to the Nyctaginaceae in Jamaica and other parts of the Caribbean. The species breeds throughout the year with a generation length of < 1 month.
2. In adult females, plots of wing length on hind tibial length, of maximum potential fecundity (m.p.f.) on wing length, and of m.p.f. on ovariole number, suggested the presence of a small morph, which the use of discriminant function analysis and other investigations confirmed. There was also good evidence of two size morphs in adult males.
3. Both body size and ovariole number had significant effects on m.p.f. but these effects were different in the two morphs. While the food plants had significant influences on size and fecundity, these were relatively small. The m.p.f. of the small morph was 125.8±11.1 eggs, and of the large morph 318.7±8.3 (95% cl).
4. Laboratory experiments on the flight performance of newly-emerged midges indicated that the small morph was not dispersive and that about 80% of the large morph was dispersive. No differences in size, wing length or fecundity could be found between the two behavioural types of the large morph.
5. The nature of the polymorphism is unusual, particularly since the dispersive individuals potentially have similar (or greater) fecundity than the non-dispersive ones.
6. Estimates of achieved fecundity (eggs actually laid, rather than m.p.f.) were 67.8±9.6 (field, minimum) and 138.9±30.4 (laboratory), the latter estimate being based on large-morph females.