196 JOURNAL OF ECONOMIC ENTOMOLOGY [Vol. 5 



The accompanying figures were obtained in this way, and do not 

 include the hundreds and probably thousands of caterpillars which 

 we know were killed at Wallingford by the lead arsenate and the 

 tanglefoot bands; neither do they include those killed by fire in the 

 walls at Stonington, but are simply a record of the insects found and 

 destroyed b}' the men working day after day. 



It should also be stated that the money expended in this work by 

 the state (.$18,681.39) includes the cost of much scouting outside the 

 infested regions, following up reports of infestations, and the travehng 

 expenses for most of the work of inspecting imported nursery stock 

 for the last three years. It also includes the cost of scouting and 

 destroying brown-tail nests in five towns in the northeast corner of 

 the state- last winter, so that the actual amount expended in gypsy 

 moth extermination would be considerably less. The Federal money 

 has practically all been used for scouting, both in and outside of the 

 infested territory. 



i^Proceedings to be continued.) 



UNCONSIDERED FACTORS IN DISEASE TRANSMISSION 

 BY BLOOD-SUCKING INSECTS 



By Frederick Knab, Bureau of Entomology, Washington, D. C. 



The study of the role of blood-sucking insects in the transmission 

 of disease is a recent one, and it is still to a large extent vague and 

 chaotic. Its teachings are not only built up largely on hastily col- 

 lected and faulty data, but they are replete with errors. Many of 

 the investigators not only have lacked the necessary knowledge of 

 biology, but the mastery of detail, along with a broader view, which 

 is eminently necessary in such work. Since the discovery that certain 

 blood-sucking insects are the secondary hosts of pathogenic parasites, 

 nearly every insect that sucks blood, whether habitually or occas- 

 ionally, has been suspected or considered a possible transmitter of 

 disease. No thought seems to have been given to the conditions, 

 and the characteristics of the individual species of blood-sucking 

 insects, which make disease transmission possible. 



In order to be a potential transmitter of human blood-parasites, 

 an insect must be closely associated with man and normally have 

 opportunity to suck his blood repeatedly. It is not sufficient that 

 occasional specimens bite man, as, for example, is the case with 

 forest mosquitoes. Although a person may be bitten by a large 

 number of such mosquitoes, the chances that any of these mosquitoes 

 survive to develop the parasites in question (assuming such develop- 

 ment to be possible) and then find opportunity to bite and infect 

 another person are altogether too remote. Applying this criterion, 



