24 N. H. AGE. EXPERIMENT STATION. [Bulletin 192 



The investigation of the present season has been laid out along the same lines 

 as that of last year, for two principal reasons: First, because the abundance 

 of the insect species under study, Phorbia brassicae, varies from year to year, 

 and this variation is reflected in the detailed records ; second, because of seasonal 

 variation in rainfall, wind, storms, and other climatological factors. 



During the summer of 1917 the work was carried forward as projected in the 

 last report. The species of insect under study was Phorbia brassicae, the com- 

 mon cabbage maggot, which normally is rather abundant on cabbages, turnips 

 and radishes in southeastern New Hampshire, including the fields adjacent to 

 the Experiment Station. As is frequently the case with many species of 

 insects, the cabbage maggot has varying abundance between wide Umits and 

 this has influenced the progress of the investigation, sometimes unfavorably, 

 because of an actual scarcitj' of the species, and, again, favorably, because 

 affording an additional angle on the results of studies. 



The studies of subterranean materials, including their kUling zone, their 

 rate of progress through soil, imder varying conditions, has been brought to a 

 close and awaits publication. 



The investigation of the season included in this report and that laid out for 

 the season now beginning is confined to materials apphed to the sm'face of the 

 soil and remaining on the sm'face, especially tobacco dust, tobacco dust and 

 ground limestone, and floiu* paste. 



As in former seasons, a system of detailed records has been maintained and 

 mil be followed during the current year. In all cases actual counts are made 

 of maggots and pupae on or adjacent to the roots of plants. This involves 

 removal of soU and sifting the same and is a rather laborious process; but it 

 gives records that are definite and is infinitely more valuable than dependence 

 on the apparent "\dgor of plants. Results of tliis part of the investigation also 

 are awaiting publication. 



A second and hitherto untried hne of inquiry will be carried out at Durham 

 and is a study of the insecticidal properties of pjTethrum or so-called Persian 

 Insect Powder and its extracts. 



It is planned to carry out investigations along the following hues : 



Efficiency of material as influenced by fineness of division of the powder. 



Influence of dry heat. 



Comparative study of contact and stomach poison properties. 



Influence of extract with water at various temperatm-es. 



Influence of extract with alcohol and ether. 



Each of these lines of studying the subject is to be approached from the 

 viewpoint of insecticidal efficiency with the use of Uving insects as the deter- 

 mining factor. At the same time it will be proposed to supplement this -ndth 

 chemical analyses wherever the facts ascertained seem to make this desirable. 



INVESTIGATIONS UNDER HATCH FUNDS. 



The Investigation of the Apple Leaf Miner and Its Reaction to 



Applications of Contact' Insecticides. 



This investigation was carried out along the Unes projected in the last 

 report. The study was continued throughout the season and yielded many 



