INSECTICIDES 355 



Some Local Problems in Insect Control 



Spray residues. Anxiety having arisen regarding the safety of sprayed 

 fruit for human consumption, analyses were made of apples which had 

 received five apphcations of lead arsenate (4 lb to 150 gal) during the seasons 

 of 1926 and 1927 at Yonkers, New York.^^- " The average amount of arsenic 

 as AsoOs was 0.173 mg per kg of fruit in 1926, with a rainfall exposure of 

 17.85 to 19.51 inches, while in 1927 the average value was 0.099 mg per kg 

 with a rainfall exposure of 33.24 inches. No sample analyzed in either year 

 exceeded the limit adopted by the Royal Commission of Arsenical Poisoning 

 in 1903 (1.429 mg per kg), the then generally accepted standard of tolerance 

 for arsenic. An average of 0.912 mg of metallic lead per kg of fruit and a 

 maximum of 1.80 mg per kg were found in 1927, the only year in which 

 analyses for lead were made. 



Failure to control cankerworms by banding leads to the discovery that 

 the larvae are wind-borne. An outbreak of cankerworms in 1933 practi- 

 cally defoliated a tract of woodland belonging to the Institute. Control 

 by spraying was not considered practical because of the rough terrain. It 

 was decided, therefore, to band the trees of a section of this woodland to 

 test the efficacy of this method of control with the \dew of banding the whole 

 tract to prevent defoliation in future outbreaks. Accordingly, trees in a 

 somewhat isolated section were banded wdth tree tanglefoot in the fall of 

 1933, and the bands were renewed the following spring. The failure of this 

 method to give any appreciable control led to the study of the efficiency of 

 banding and a search for the cause that made it ineffective." 



In the United States the term "cankerworm" is restricted to two species 

 of Geometridae, the fall cankerworm (Alsophila pometaria Harris), and the 

 spring cankerworm (Paleacrita vernata Peck). The larvae of these two 

 species are commonly called inchworms, measuring worms, span-worms, 

 or loopers, because of their size and peculiar looping habit of locomotion. 

 When disturbed the larvae drop, supported by silken threads. The two 

 species have much in common and outbreaks often occur simultaneously. 

 They attack elm and apple and feed on a wide range of deciduous host 

 plants. 



The adult female moths of both species are wingless and ascend the trunks 

 of the trees by crawling to lay their eggs on the bark of the branches and 

 twigs. The fall cankerworm female moth ascends the trunks of the trees 

 in the fall to lay its eggs, while the spring cankerworm female moth ascends 

 the tree trunks in the spring for egg-laying purposes. The eggs of both 

 species hatch in the spring about the time apple blossoms show pink, 

 t If trees are banded both in the autumn and spring well in advance of the 

 emergence of the females of the fall and spring cankerworms, the female 

 moths are impaled and thus oviposition is prevented. Control of canker- 

 worms by various methods of banding has been a common practice for 

 nearly a century in eastern United States. 



