12 N. H. AGR. EXPERIMENT STATION. [Bulletin 203 



Careful studies of eggs in contact with the tobacco-dust-lime mixture 

 showed a definite insecticidal action. In one series eggs placed in contact 

 with soil in the normal manner gave a 100% hatch, whereas eggs placed in 

 contact with the mixture gave a percentage of hatch ranging from zero to 

 31%. In a second series, the percentage of hatch in the treated lots was 

 14% while ia the check lots it was 82%. In a third series the hatch in the 

 treated lots was 5% and in the check lots 71%. 



Counts of larvae and pupae on the roots of plants which had received 

 the mixture indicated a failure of larvae to reach the roots on treated plants 

 for a period of several days following the treatment, but later an increasing 

 number of larvae appeared on the roots. This phase of the study has a 

 definite bearing on eventual use of the treatment, because the more serious 

 damage is done by the maggots that reach the roots early, before the plant 

 is well established and before it has built up an extensive root system. Thus, 

 60 plants which had been treated with tobacco-dust-lime showed at the 

 end of four weeks 29 pupae, whereas 60 check plants showed 158 pupae. 

 A parallel experiment with 75 plants treated with the mixture gave 82 pupae, 

 where 75 check plants gave 162 pupae. 



The addition of moisture to simulate rain, after newly-deposited eggs 

 had been placed in contact with the mixture, resulted in a hatch of 16% 

 as compared with a hatch of 93% where the eggs were placed in contact 

 with soil, and water added. On the other hand, where eggs were placed 

 on soil and wet down with an infusion made by permitting the mixture to 

 stand in water, the percentage of eggs that hatched was nearly as great as 

 that of check plots. 



Experiments carried out to determine whether maggots on the roots of 

 plants are killed by infusions of the mixt.ure carried down through the soil, 

 gave inconclusive results. There was a mortality varying from 4% to 10% 

 as compared with a mortality of O^c in the case of the checks. Also, 

 in the case of pupae, carried through a similar series of experiments; the re- 

 sults were inconclusi\e. The number of flies emerging in the case of treated 

 pupae varied from 0% to 6% as compared with 10% in the case of the checks. 



Experiments to determine whether flies lay eggs as freely in the case of 

 treated plants as in the case of checks gave interesting results. The plants 

 in these experiments were set out at a time when ovipositing flies were abun- 

 dant, and treatment was applied immediately. Examination of these and 

 of checks was begun two days later and was continued every 48 to 72 hours 

 for four weeks. Egg-laying began promptly on the checks. The number 

 of eggs recorded on the checks increased in the various observations and 

 reached 199 eggs on 25 plants at the 14th day. In the case of the two lots 

 of 25 plants each, treated with the mixture, 2 eggs were observed in the case 

 of one lot on the 8th day and 1 egg in the case of the other lot on the 11th day. 



A very heavy rain on the 16th day was followed promptly by visits of 

 large numbers of fliep to the treated plants showing that hea\'y rains rapidly 

 reduce efficiency. A further treatment four days after the rain again ap- 

 peared to give protection. 



Observations to determine the possible utility of a poison bait, consisting 



