304 JOURNAL OF ECONOMIC ENTOMOLOGY [V^ol. 14 



The only experiments with white arsenic were the two plats sown 

 with a commercial citrus fruit pulp mixture (Mackie, 1920),'* diluted 

 with bran, but a poor killing was made in both cases. In fairness, it 

 should be stated that this preparation is recommended by the manu- 

 facturers as a grasshopper poison. While the results on these two plats 

 were almost identical, they are not regarded by the writer as conclu- 

 sive. Perhaps the conclusions of Davis and Turner (loc.cit.) to the 

 effect that white arsenic was less effective than Paris green with the 

 true army worm are evidenced here in these results with this insect. 



Some confusion developed dining this outbreak over the terms "white 

 arsenic" and "lead arsenate", or "arsenate of lead." In several instances 

 arsenate of lead was sold instead of arsenic, and was mixed in the 

 bran mash at the proportions prescribed for arsenic. Two sowings of 

 this mixture failed to check the larvae appreciably. In one instance, 

 paste arsenate of lead was sold a fanner in place of arsenic without ex- 

 plaining the substitution. Paris green has an advantage of not being 

 readily mistaken for other substances, and in the mixing shows up well 

 on the bran flakes. 



Parasitic Tachinid adults were plentiful at all times during this out- 

 break, but the percentage of larvae with the ivory white eggs on their 

 bodies varied greatly between fields. Itn one field, early in September, 

 a parasitism of about 95 per cent was found. On the college farm, at 

 the same time, the parasitism was four per cent, but later increased to 

 about 50 per cent. Winthemia quadripusinlaia Fabr., was the more 

 common Tachinid in the fields. About SO adults of Muscina stahulans 

 Fall, emerged from 100 fall army worm larvae collected in the field and 

 placed in a jar for rearing parasite adults. Dr. Aldrich states with 

 the determination of the specimens that ' ' the larvae according to Keilin 

 is saprophagous imtil near the end of the second stage, then becoming 

 predaceous on other dipterous larvae. It is not a parasite, but the fly 

 lays its eggs where there are other dipterous larvae." It is believed 

 that relatively few larvae bearing Tachinid eggs upon their bodies died 

 as a result of the parasitic larvae. It is well known that if the host ' 

 molts before the parasite egg hatches, the egg is discarded with the molt. 

 It is doubtful if the larva into which the parasitic larva has entered 

 takes any food thereafter. 



It was found that when larvae bearing eggs of Tachinidae upon their 

 bodies are killed by poisoned bran mash that the parasites did not de- 

 velop. There were no exceptions in a batch of 100 larvae, i.e., no para- 



^Mackie, D. B., 1920. A Prepared Grasshopper Poison. Monthly Bui. Dept. 

 Agri. Cal. IX, No. 5-6, pp. 194-197. 



