112 



resorted to ; for the latter a dust of 3 parts sulphur to 1 part lead 

 arsenate proved effecti\'e. 



Experiments with pecan insects have shown that the pecan-leaf 

 case-bearer [Acrobasis ncbiildla] should be treated with liquid lead 

 arsenate rather than dust or calcium arsenate. For the obscure 

 scale [Chrysomphalus obsciints] on pecan, crude oil emulsion or lime- 

 sulphur solution in winter strength should be apj^lied during early 

 spring, before the buds are out. Against the pecan weevil [Balamniis 

 canuw] spraying and dusting experiments were unsuccessful. Fumi- 

 gation, of harvested nuts with carbon bisulphide, using ^ oz. per 

 bushel of nuts, and fumigating for 24 hours, proved effective. This 

 method, however, is only partially successful, since a considerable 

 portion of the larvae in some regions leave the pecans before harvest 

 time. The walnut husk maggot, which was originally a pest of black 

 walnuts only, is now attacking Persian and Japanese walnuts in the 

 eastern part of the country. The maggots mine through the husk, 

 causing the nuts either to drop prematurely or to adhere to the branches 

 be^-ond the regular harvest time. Investigations on this insect will 

 be published shortly. Several species of walnut and hickory curculios 

 are also being studied ; these attack tlje immature nuts, causing many 

 of them to fall. Conotrachclus retciitus oviposits in black walnuts 

 that are about one-fourth grown, from 50 to 90 per cent, being infested 

 in some locahties. Other weevils attacking chestnut and hazel are 

 also being studied. 



Investigations of miscellaneous insecticides have been continued. 

 From experiments on thousands of insects, it appears that the per- 

 centage of water-soluble arsenic in arsenicals before they are taken 

 in by insects has little to do with their toxicity, althcuigh those in which 

 the arsenic content is nearly all water-soluble generall}' give the 

 highest rate of toxicit}^ The higher the percentage of arsenic rendered 

 soluble inside the bodies of insects, the higher, as a rule, is the rate 

 of toxicity, and the more arsenic retained in the insects as compared 

 with that voided, the higher is the rate of toxicity. It is evident 

 that only an indefinite opinion concerning the killing power of an 

 arsenical can be inferred from its composition, but results indicate 

 that the toxicity depends directly upon the amount of arsenic rendered 

 soluble inside the insects, and this solubility dei)cnds directly upon the 

 stability of the compound. 



Vegetable pests include the sweet potato weevil [Cylas formic ariiis], 

 but clean cultivation and co-operation among farmers and the 

 planting of uninfested potatc~)es have produced a great decrease 

 in infestation. Alabama, where 30 farms were infested, can now be 

 declared free from the pest. A weevil-free zone 30 miles in length is 

 being maintained on the eastern coast of Florida through the destruc- 

 tion of the food-plant, morning glory [Ipomaea], and the only infested 

 plot of this plant on the mainland of Mississippi has also been destroyed. 

 The Colorado potato beetle [Leptinotarsa dcccmlincata] has been 

 scarce in Maryland and Virginia, doubtless owing to late spraying, 

 parasites and severe winters. Against the potato leafhopper 

 [Empoasca mali] Bordeaux mixture proved a satisfactory repellent, 

 while nicotine sulphate and kerosene emulsion were ineffective. 

 The tarnished plant bug [Lygus prafensis] severely injured potatoes 

 in some localities ; its wild food-plants and breeding-places are being 

 studied. The bean lad\^bird [Epilachna corrupia] has been trouble- 

 some in Colorado and New Mexico, except where thorough spraying 



