CHENG and SHULENBERGER: DISTRIBUTION AND ABUNDANCE OF HALOBATES 



130° 120° 110° 100° 



110° 100° 90° 



Figure 7. — Halobates splendens distribution, as in Figure 3. 



of the water in anything except calm weather, 

 making estimation of area sampled or volume fil- 

 tered difficult; and 2) these insects are known to 

 avoid nets but the extent of avoidance is unknown 

 (Cheng 1973c; Cheng and Enright 1973). However, 

 the samples used in this study resulted from repli- 

 cate tows and may therefore be reasonably com- 

 pared with one another and used to set lower 

 limits on abundance. 



Our data showed that in//. micans,H. sobrinus, 

 and H. splendens numbers of adults are about 

 twice that of nymphs (Table 2). This may be a 

 result of several factors: 1) nymphs might avoid 



the net more actively than adults (unlikely); 2) 

 nymphs are smaller than adults and may wash 

 through the meshes of the net more easily (possi- 

 ble); 3) nymphs might have been missed in sorting 

 (unlikely; samples have been rechecked); and 4) 

 aspects of their natural history might produce 

 such a distribution (e.g., heavy predation on 

 nymphs plus long life-span of adults). Data do not 

 exist to test hypotheses 1) and 4). We can offer no 

 explanation for the differences between H. 

 sericeus and the other three species. 



Since//, micans and//, sobrinus accounted for 

 almost 909c of total individuals caught (65.6 and 



587 



