1920] ECONOMir ZOOLOCJY — ENTOMOLOGY. 855 



most when intrndiicod sinply into tho l»oiizt>no rinp jiro in order of ImportJince 

 the methylamido (most effective), dimethylamido, hydroxy, nitro, amido, 

 iodin, bromin, chlorin, methyl groups (least effective). But this order is 

 moditied in presence of another group; thus, when there is a CHs already present 

 in the ring, the order becomes chlorin (side chain), amido, hydroxy, chlorin 

 (ring), methyl. Clilorin and hydroxy groups together give rise to highly 

 poisonous substances considerably more effective than where present separately. 

 The association of chlorin and nitro groups in chloropicrin gives rise to one 

 of the most toxic substances tested. Methyl groups substituted in the amido 

 group of aniline increase toxicity more than if substituted in the ring. Com- 

 pounds with irritating vapors have usually high toxic values, e. g. allyl 

 isothiocyanate, chloropicrin, benzyl chlorid. 



"The toxic values of these substances are not closely correlated with their 

 vapor pressures or rates of evaporation. Tliere is a fairly close relationship 

 between toxicities and the vapor pressures, rates of evaporation, and volatili- 

 ties of compounds of the same chemical type. In a series of similar compounds 

 decreases in vapor pressure and in volatility are associated with an increased 

 toxicity. A possible explanation is that condensaticm or adsorption takes place 

 along the tracheal system when insects are submitted to the action of these 

 vapors. On exposure once more to the open air these vapors diffuse out into 

 the atmosphere, the rate at which they do so being a measure of the rapidity 

 with which the insect recovers. A limit is put upon toxicity by the decrease 

 in vai)or pressure when it sinks too low to allow a toxic concentration in the 

 vapor phase. 



" Chemically inert compounds boiling above 170° C. are generally uncertain 

 in their poisonous effect on wireworms after an exposure of 1,000 minutes at 

 1")°. Nearly all organic compounds boiling above 215° are uncertain in their 

 action, while those boiling above 245° are nontoxic. These limits depend on the 

 resistance of the insect, the length of exposure, and the temperature at which 

 the experiment is carried out." 



The ribbed pine-borer (Rha<>;iiim lineatum Oliv. ), W. N. Hess (Neio 

 York Coniell Sta. Mem. SS (1920), pp. 367-Ml, pi. 1, figs. 6).— This is an ac- 

 count of one of the commonest and most widely distributed species of ceram- 

 bycids occurring in North America, being especially abundant in the vicinity of 

 central Pennsylvania and about Ithaca, N. Y., where the study was conducted. 

 The species, which was originally described in 1795, is commonly and widely 

 distributed throughout the greater part of North America, and probably ranges 

 in distribution from northern Mexico to central Canada, extending across the 

 continent from coast to coast wherever pine is found. In New York and Penn- 

 sylvania all the ccmimon species of pine are attacked by it, the white pine, 

 pitch pine, and red pine being most commonly found infested. The author has 

 never found it to infest other conifers, such as larch and spruce, though he 

 considers it possible that they may be attacked by it. 



In the strict .sense it can hardly be considered as an insect of economic im- 

 portance in so far as any damage to living pines is concerned. Its attack is 

 limited to the region of the inner bark and the outer sapwood, and it doubt- 

 less causes considerable damage to recently dead timber. Its excavations are 

 usually extensive, and as a result the bark is frequently loosened, allowing 

 moisture to enter. Water having once gained access is held by the large masses 

 of frass. which furnish a condition favorable to fungus growth, thus hastening 

 the decay of the tree. " During the second and third years after the trees die 

 the exit boles made by the emerging adults admit large qiiantities of water, 

 other insects, and fimgi. by means of which the log is soon rendered useless 

 for commercial purposes." 



II 



