AGRICULTURAL RESEARCH IN NEW HAMPSHIRE 39 



"master hatch" it may be presumed that onl\^ a part of the particles in the 

 final product carry the toxicant. In the method used in the laboratory it 

 is presumed that substantially all of the particles carr\' the toxicant, but 

 in reduced amount. 



A series of experiments w ere run in which the performance of given 

 toxicants was studied when present at a pre-determined percentage in an 

 inert by the master batch method, as compared with those prepared by 

 the direct impregnation method. The data indicate that a given amount 

 of toxicant exhibits greater performance when added to an inert dust by 

 the direct method than when added by the master batch method. The 

 difference in favor of the direct method is frequentlx' as much as two to 

 one. 



This investigation appears to be the first that has been conducted 

 comparing the t\\'o methods of preparing contact insecticide dusts. The 

 results of the stud)' are probably important as pointing the way toward 

 more efficient use of both natural and synthetic contact insecticides when 

 applied in dust form. 



W. C. O'Kaxe, L. C. Glover, J. W. Exke 



Penetration of Ovicides 



Investigations of contact insecticides are supplemented by similar in- 

 vestigations of ovicides wherever suitable material is available. The tech- 

 niques emplo)'ed are similar and the chemicals under study are frequently 

 the same. Chemicals which indicate toxicity as contact insecticides 

 against the mobile stage of insects are further studied as to their toxicity 

 when applied to the egg stage, especially chemicals soluble in oils. In the 

 light of earlier w ork by the department, these ovicides ma>' be expected to 

 penetrate the resistant surface of an insect egg. 



Apparatus was constructed in the department greenhouse by means 

 of which applications of materials could be made to insects present on 

 plants during and after the egg stage. A toximeter \\ as constructed which 

 was provided with a revolving turntable and with two sources of atomized 

 spray delivered from opposite points to a plant revolving on the turntable. 

 In addition, racks were constructed on M'hich potted plants could be 

 placed after application of chemicals. The pots stand in shallow trays 

 containing water. The plant itself is enclosed within a spherical cage 

 which is suspended in such a \\'ay that the plant does not support the cage. 

 Thus, insects are confined on the plant, but with free access of air. At 

 the same time, observations can be conducted without removing the cage. 



Eggs of the Mexican bean beetle were included in tests of new ma- 

 terials which might serve as ovicides. No materials were discovered 

 which are toxic to these eggs without at the same time being toxic to the 

 plants on which the eggs are laid. 



Further studies are provided for in which it is expected to use potted 

 apple seedlings infested with a species of aphid. The upper part of a 

 seedling can be confined vithin the cage described above. It is hoped 

 that by suitable control of temperature, egg stages of these aphids may 

 be obtained for further studies of the penetration and toxicity of 

 ovicides. 



W. C. O'Kane 



