278 



SCIENCE 



[N. S. Vol. XXIX. No. 737 



checks in the Mississippi Valley it is supposed 

 that the efficiency of the parasites will be pro- 

 portionately much greater than it has been else- 

 where. Practical experiments have been conducted 

 which show that the artificial introduction of 

 parasites that have adopted themselves to the 

 boll weevil in Texas is a hopeful line of assistance 

 to the cotton planter. 



Investigations of Toxoptera graminum and its 



Parasites: by F. M. Webster. 



This is a species of aphis which on account of 

 its depredations has come to be known in the 

 grain-growing sections of the southeast and south- 

 west as the green bug. Invasions occur at irreg- 

 ular intervals both in this country and in Europe, 

 when it breeds in immense swarms, not only 

 proving exceedingly destructive, but the winged 

 insects flying or drifting about in clouds, some- 

 times becoming troublesome to people. 



It is known to occur in southern Europe, Hun- 

 gary, Belgium, in Siberia and in the Orange River 

 Colony, South Africa. In the United States it 

 extends from Mexico and the Gulf northward to 

 Canada, excepting in the central New England 

 states. It also occurs on the Pacific coast. It 

 inhabits elevations of only a few feet above the 

 sea level to the high plateaus of the west at an 

 elevation of eight thousand feet. 



While preferring grain, especially oats, it breeds 

 on the following grasses: Poa pratensis, which is 

 a common food plant all over the north; Alope- 

 curus genioulatus, Agropyron ocoidentalis and 

 Hordeum pusillum in Oklahoma, Kansas and Colo- 

 rado; Agropyron tenerum, Bromus portei, Elymus 

 striatus, Hordeum ccespitosum, Polypogon mon- 

 speliensis and Stipa vividula in New Mexico; 

 Distichlis spicata and Hordeum jubatum in Mon- 

 tana; Setaria glauca in Indiana; and Daotylis 

 glomeratus in the northern states and Virginia. 

 In the northern section of the country its prin- 

 cipal food plant seems to be blue grass. 



Its destructive outbreaks in the United States 

 seem to be regulated by the mild winters and cold 

 springs, not so much on account of the influence 

 of temperature upon the insect itself as upon its 

 principal parasite Lysiphleius tritici which ordi- 

 narily holds it in check. Wintering over in the 

 north in the egg stage; in the central portion of 

 the country as far south at least as Tennessee and 

 southern Kansas, both in the egg and as viviparous 

 females; and as the male and sexual female of 

 Toxoptera graminum may also occur in the spring, 

 it seems quite possible that in the far south, in the 

 region of the Rio Grande River, this aphid may 



pass the dry season instead of the winter in the 

 egg stage, although this has not yet been proved. 

 While the egg-laying female is quite distinct from 

 the viviparous female, individuals frequently occur 

 that are both oviparous and viviparous. The 

 oviparous female produces very few eggs, probably 

 not to exceed a half dozen. The young hatching 

 from these eggs are all of them viviparous fe- 

 males and in the north these continue to remain 

 viviparous until fall and sometimes even through 

 the entire winter. 



The principal parasite, Lysiphlebus tritici, is 

 parthenogenetic, the offspring of virgin females 

 being usually all males. Occasionally there are 

 females, and these being kept virgin have pro- 

 duced an occasional female to the third generation 

 from the mated female. These parasites deposit 

 their eggs singly in the body of the Toxoptera, and 

 the larva when it becomes full grown lines the 

 now empty body of its host with silken threads 

 and attaches the cocoon to the leaf of the plant. 

 These cocoons cause the body of the host to assume 

 a rotund appearance and brownish color and where 

 the insect is excessively abundant and the para- 

 sites increasing rapidly these brown bodies become 

 so thick as to give a field of wheat or oats ob- 

 served at a distance a brownish tinge. 



Other insect enemies are the lady beetles, 

 Coccinellidae, a minute Aphelinus and probably 

 a larva of a small fly belonging to the genus 

 Leucopsis. 



M. C. Maesh, 

 Recording Secretary 



THE NEW YOBK ACADEMY OF SCIENCES. SECTION 

 OF ASTRONOMY, PHYSICS AND CHEMISTRY 



At a meeting held at the Museum of Natural 

 History, on Monday, January 18, Dr. 0. W. Will- 

 cox presented a paper entitled " Cylindrogenite, 

 a Possible Representative of a Cylindrical (Non- 

 Hauyan) Order of Crystals," in which he de- 

 scribed a remarkable new form of limonite which 

 occurs in the Red Bank sand of the Upper Cre- 

 taceous of New Jersey. The limonite, var. Cylin- 

 drogenite, occurs normally as perfect cylinders 

 (which may be either hollow or solid), terminated 

 at either end by a cone or a hemisphere. Two or 

 more cylinders frequently intergrow, forming ag- 

 gregates in which each cylinder preserves the 

 alignment of its own axis; a number of such 

 aggregates and also a number of photographs were 

 exhibited. A most careful and painstaking study 

 extending over more than three years having failed 

 to suggest any other possible origin for these 



