GIPSY-MOTH LARV^ AS AGENTS IN THE DISSEMINA- 

 TION OF THE WHITE-PINE BUSTER-RUST^ 



By G. Flippo GravatT, Assistant Pathologist, and G. B. PosEy, Scientific Assistant, 

 Investigations in Forest Pathology, Bureau of Plant Industry, United States Depart- 

 ment of Agriculture 



INTRODUCTION 



Very little has been done to correlate the widespread distribution of 

 the white-pine blister- rust, caused by Cronartium rihicola Fischer, with 

 factors governing the dissemination of the spores of the causal organism. 

 The early occurrence of telia on leaves of currant and gooseberry plants 

 (Ribes spp.) in localities distant from known infections on pines (Pinus 

 spp.), together with the absence of definite knowledge of instances of 

 overwintering on the former hosts, is suggestive of distant seasonal 

 spread of the disease by aeciospores from pines. 



Larvae of the gipsy moth (Porthetria dispar L.) feed on the Peridermium 

 stage of Cronartium rihicola and carry thousands of . aeciospores on their 

 bodies. As Collins^ found that larvae of the gipsy moth are blown as 

 far as 20 miles, these insects are a potential agent in distant spread of 

 the blister-rust. The gipsy moth is distributed over a large portion of 

 the white-pine region of New England. 



GIPSY-MOTH INFESTATION ON DISEASED PINE 



In the fall of 191 6 a stand of white pine covering an area of from 5 to 

 7 acres at Kittery Point, Maine, was found to be severely infected with 

 Cronartium rihicola. This growth ranged from young seedlings to mature 

 trees 80 feet tall and random ]4-a.cre plots in this area showed 65 to 

 100 per cent of the trees to be diseased. The number of infections on 

 individual trees ranged from i to more than 300, and it was estimated 

 that there were 75,000 to 100,000 separate infections in trees on this 

 area. 



In the infected plot gipsy-moth-egg clusters were found in varying 

 abundance on limbs and stems of pines of all sizes, and were located 

 from near the ground to the tops of the largest trees. In a number of 

 cases egg clusters were present on the diseased bark, and in one instance 

 four were located on a single canker. 



« The writers are indebted to Mr. A. F. Burgess, of the 0£Gce of Gipsy Moth and Brown-tail Moth In- 

 vestigations, Bureau of Entomology, for helpful suggestions. Further work is being carried on in co- 

 operation with the aboTe office. 



' Collins. C. W. dispersion of gipsy moth larv^ by the wind. U. S. Dept. Agr. Bui. 273, 23 p., 

 7 pi. 1915. Bibhography, p. 22-23. 



METHODS USED IN DETERMINING WIND DISPERSION OF THE GIPSY MOTH AND SOME OTHER 



INSECTS. /« Jour. Econ. Ent.. v. 10. no. i. p. 170-176, 2 pi. 1917- 



Journal of Agricultural Research. Vol. XII, No. 7 



Washington, D. C. Feb. 18, 1918 



mb Key No. G 135 



(459) 



