TWO BACTERIAL DISEASES OF INJURIOUS INSECT LARVAE. 



E. Melville DuPorte, Macdonald College. 



1. A Bacterial Disease of the Tent Caterpillar. 



The tremendous devastation in our orchards, forests and woodlands 

 caused by the tent caterpillars during the past three seasons has again 

 brought forcibly to our minds the great economic importance of these 

 insects. The problem of the control of injurious insects by their natural 

 parasites is a live one at the present day, and during an overwhelming 

 attack by any injurious form the first question one asks is, "Can it be con- 

 trolled by natural 'means?" During normal years the tent caterpillars 

 are kept in check by several dipterous and hymenopterous parasites. It 

 is only when, for some reason, the numbers of these parasites become 

 very small, that the caterpillars have a chance to increase and, owing to 

 the large number of eggs laid, their potential increase is so great that they 

 can in one or two seasons become as overwhelmingly destructive as they 

 have recently been. Owing to this it is doubtful whether it would be 

 practicable to breed and conserve a suiificient number of these parasites 

 to be of immediate use in the control of these insects during one of their 

 periodically recurring epidemics. We, therefore, turn our attention to 

 infectious or contagious diseases. Can these insects be controlled by 

 the dissemination of the germs of bacterial disease? With this question 

 in mind last season, I tried to isolate the causal organism of a disease 

 which has been much in evidence here among these insects and which 

 has acted as an important factor in their control. 



On June 5th I collected a number of diseased caterpillars of Mala- 

 cosoma americana, the orchard tent caterpillar. A microscopical prep- 

 aration of the diseased and disorganised tissue showed the presence, 

 in large numbers, of a large spore bearing bacillus. Plates were made 

 from this diseased tissue and cultures of an organism similar in appear- 

 ance to that seen in the tissue were obtained and isolated. The following 

 inoculation experiments were conducted. 



1. Cage A. 



June 8th. — Inoculated hypodermically 13 specimens M. americana 

 with a suspension of the organism in sterile water. 



June gth. — 4 caterpillars dead. 



June loth. — 5 others dead (1 drowned), 1 living, 3 missing (escaped 

 from cage). 



