57 

 Lottin: Introduction 



forms can be calculated. Nets similar to a plankton 

 net may be used to sample the free-swimming insect 

 fauna of the open water, particularly those forms 

 such as Chaoborus that migrate between the bottom 

 and the surface of the water. 



Miscellaneous techniques for quantitative sampling. 

 —The Berlese funnel is useful in obtaining small 

 insects, often overlooked, from the bottom debris of 

 streams and lakes. The trash is collected and blotted 

 to remove the excess water and then placed in the 

 funnel. The recovery of the specimens is made in 

 the manner previously mentioned. Drift nets (P. R. 

 Needham, 1928) may be stretched across a stream at 

 surface level to sample floating organisms, especially 

 terrestrial forms that fall onto the water and provide 

 an important part of the food of fish. Unfortunately, 

 such nets are quickly fouled and hence must be 

 cleaned frequently throughout the day. Smaller nets 

 may be used to sample a limited area of surface but 

 here again, fouling occurs and back eddies carry 

 organisms around and past the net. Pumping and 

 draining parts of a stream, after damming and by- 

 passing the water, will reveal the total population 

 of conspicuous insects over a given area. Sialis 

 larvae, for example, are revealed as very abundant 

 in some streams when pumped and drained but are 

 seldom taken in riffle samples. 



The microscopic biota associated with the surface 

 of rocks and other objects in the water (periphyton) 

 is an important source of food for insects. It may be 

 sampled through the use of collodion (Margalef, 1949; 

 Wenzl, 1940, 1941). The rocks to be examined are 

 collected in 5 per cent formalin solution. They are 

 next stained with Delafield's haematoxylin, washed 

 in distilled water, and run through a series of 

 alcohols, ending in absolute alcohol mixed with ether. 

 The process up to this time takes about four hours. 

 The stones are picked out of the solution and imme- 

 diately covered with a solution of collodion dissolved 

 in alcohol and ether. They are then allowed to dry 

 completely. This process takes only a few minutes. 

 After the solvents have dried, the collodion film is 

 peeled off with a pair of sharp forceps, and a micro- 

 scopic examination made of the contents. Quantitative 

 counts may be made through the use of calibrated 

 ocular grids on the microscope. Permanent slides 

 can be made of the film by mounting it in Canada 

 balsam and covering with a glass cover slip. Margalef 

 ran repeat tests on "used" stones but found that the 

 original treatment removed all the microorganisms 

 from the surface of the rock. 



Most sampling methods (Surber, Hess, drag-type, 

 and the like) require time-consuming hand picking of 

 individual organisms. This essential step may require 

 so many man hours that adequate sampling becomes 

 impractical. To obviate this, a calcium chloride flo- 

 tation method has been employed with some suc- 

 cess (Welch, 1948). The basis of the method is 

 to alter the specific gravity of the liquid so that 

 insects will float to the surface while rocks and 

 trash remain at the bottom. A CaCl 2 solution with 

 a specific gravity of 1.1 is placed in a bucket. Un- 

 sorted trash from a Surber sampler, for example, is 



emptied into the bucket, and the net tfl rinsed to 

 dislodge clinging organisms. The trash ie then mixed 

 and swirled to help Loosen insects from crevi< 

 All but the heavy case-enc umbered caddiswornui and 



mollusks may bo floated in tins way. 



Whether or not CaCl 2 is used, a circular motion of 

 the hand will swirl tho water in the bucket and float 

 organisms free of the heavier debris. Then, while 

 the water is still turning rapidly, it is poured through 

 a 24-mesh sieve to concentrate die organisms. The 

 solution should be poured through a rather small, 

 single area on the sieve bottom to avoid spreading 

 the organisms. The reason for this is that in the 

 next step, when transfer of tho organisms to a preser- 

 vation jar is made, the solution is gently back-poured 

 through the sieve while tilting it over the opening of 

 a wide-mouth jar. If the organisms are concentrated 

 close to the edge of tho brass frame of tho sieve in 

 a small area, it is much easier to decant them into a 

 jar than if they are spread all over the 8-inch sieve 

 bottom. If they do become widely spread over the 

 bottom, it is easy to concentrate them again by hold- 

 ing the sieve in an inch or so of solution and gently 

 swirling it in a circular movement. A small, "pouring" 

 bottle should be carried to flush the fluid back through 

 the sieve. As a final precaution, the person sampling 

 should carefully examine the remaining trash in the 

 bucket to make sure that it is clean and does not 

 contain any organisms. It is important that no sand, 

 gravel, or small stones be decanted from the bucket 

 into the sieve or from there into the preservation 

 bottle because such materials may grind and break 

 up the tender, soft-bodied insects and other inverte- 

 brates (P. R. Needham, unpubl.). 



Once the sample has been transferred to a preserva- 

 tion jar, 70 per cent alcohol should be added and the 

 sample properly labeled. Care should be taken to 

 prevent dilution of the preservative with water already 

 poured into the jar with the organisms. To avoid 

 excessive dilution, once the organisms have settled 

 to the bottom the surplus water may be decanted, 

 leaving only about a quarter of an inch in the bottom. 

 Then if the bottle is filled to the top with 70 per cent 

 alcohol, dilution, though still occurring, is reduced 

 to a minimum. 



Later, in the laboratory, samples may be drained 

 and dried on blotting paper for one minute and then 

 weighed (wet weight). Final counting (total numbers) 

 and sorting for identification may be done in shallow 

 trays, and individuals of a given species may then 

 be stored in vials as described below. 



KILLING, PREPARING, AND STORING MATERIAL 



It frequently happens that insects are collected with 

 great enthusiasm and care and then left to deteriorate 

 in a museum box or collecting bottle. This kind of 

 neglect is wasteful of time and money and retards the 

 development of science. The proper care of specimens 

 is not a simple or invariable matter. Each group of 

 organisms requires special handling, and collections 

 are dealt with in different ways, depending on the 



