THE KiyiERKCKN mMM JQURNSI,. 



443 



k^A^ ^ m/k^AmtkmAi^Am^Amk jh^^^^'^^^^'^ .^^^^^^^^.^^^ 



answer all the questions sent to me, 

 and anticipate others, perhaps. It is 

 as follows : 



The present season is characterized 

 by one of those wide-spread and very 

 damaging insect invasions that is so 

 discouraging to the farmer. I refer 

 to the present onslaught on the wheat 

 crop by the grain aphis or plant louse, 

 Aphis avcna;. This louse attacks wheat, 

 barley, oats and rye, and is to be founti 

 in small numbers on these grains every 

 year. This year occurs one of those 

 terrible attacks that seem to thi-eaten 

 very serious loss. This raid extends 

 from Ohio west to Indiana, and north 

 to Grand Rapids, Mich. Of this much 

 I am certain. I do not know whether 

 it reaches in such overwhelming num- 

 bers to other States or not. So abun- 

 dant are these lice that they have at- 

 tracted wide attention and awakened 

 serious alarm. For the past two weeks 

 I have received daily numerous speci- 

 mens of these lice with the inquiry : 

 What is to be the outcome of this at- 

 tack ? I have received as high as 15 

 such communications in a single da}'. 



i;«riiat is It? 



This is a plant louse, or aphis, and is 

 very similar to those that attack our 

 house plants, cherry, plum and apple 

 trees, cabbages and hops. Indeed, so 

 numerous are the species of these lice 

 that hardly one of our valued plants 

 but has its plant-louse enemy. These 

 plant lice have flask-shaped bodies, are 

 usually green or black, though some- 

 times they are yellow or red, and are 

 usually quite small. In looking at the 

 gi'ain aphis at this season, four forms 

 will be seen : A small wingless louse, 

 a large wingless form — the full grown 

 apodous or wingless louse ; the pupa 

 of the winged louse which has short 

 wing pads ; and the mature winged 

 louse. We usually find these four 

 forms at some season of the year in all 

 plant-lice colonies. 



Frequently, and this was true a few 

 days ago of this grain aphis, we only 

 find the wingless forms. Later the 

 pupre with wing-pads and the fully 

 developed winged forms are seen. 

 These winged lice are doubtless de- 

 veloped that the lice may spread be- 

 fore their food is wholly destrojed, 

 and they are confronted by famine. 

 The mature wingless louse of this grain 

 aphis is about one-tenth of an inch 

 long. The winged louse is nearly 

 twice as long to the end of the wings. 



This louse is not quite as slim as is 

 Aphis mali (see Fig.) As will be ob- 

 served by examining the lice, or by 

 studying the figure, these lice have 

 long, seven-jointed antennre — the horn- 

 like organs appended to the head, and 

 the winged lice have simple veined 

 wings. The main vein of each wing 

 is branched. There are four branches 



in the front or primary wings. The 

 outer one is strongly curved, and the 

 next one branches twice. There are 

 two simple bi'anclies on the posterior 

 wing. This style of venation is char- 

 acteristic of the genus aphis. We also 

 note (see Fig.) that there are two 

 short spine-like projections, black in 

 the grain aphis, ou the hind part of 

 the abdomen. These are the nectaries 

 or honey-tubes ; so called because there 

 fre(iuently exudes from them a nectar 

 whiclt attracts ants and bees to these 

 lice. 



Just now (June 26, 1889) a species 

 of plant louse on our Norway spruces 

 are secreting nectar so profusely that 

 in the early morning it stands on the 

 leaves in drops, so that it can be tasted. 

 It seems very pleasant to the taste, 

 and is giving the bees a fine harvest. 

 This peculiar physiological charactei'- 

 istic serves the louse in this way : by 

 attracting ants, wasps and bees, the 

 birds and insect enemies of the lice are 

 frightened awaj'. I find that the oats 

 and wheat are visited by ants that the 

 nectar secreted by this grain aphis 

 may be secured. The beak of this 

 grain aphis is strong, dark in color, 

 and about one-third the length of the 

 bodj'. With this the louse sucks the 

 sap and devitalizes the plants. The 

 feet and joints of the legs, and also 

 the antennaj are dark or dusky in 

 color. 



The color in these lice varies greatly. 

 Early in the season while they are on 

 the leaves or stalks they are green. 

 This is the color now of all healthy 

 lice on the oats. After they migrate 

 to the heads they often turn yellowish 

 green, and even rust red, though I 

 find that now the green color prevails 

 even with the lice which are gathered 

 thickly about the kernels. Some of the 

 winged lice are very dark, almost 

 black. It is probable that the nature 

 of the food affects the color. As the 

 berries mature I think the yellow and 

 red colors will prevail to a larger 

 degree. 



Reproduction of the I>ice. 



The reproduction of plant lice is very 

 curious. Late in the season we finil 

 both sexes. This is the only time that 

 we find males. The sexes now pair, 

 and eggs are laid about buds, in 

 crevices, or where they will best sur- 

 vive the winter. In the spring only 

 females hatch from these eggs. These 

 do not lay eggs, but each gives birth 

 to from three to li\c lice each day. In 

 about four or five days these young 

 lice begin to produce living lice, each 

 contributing daily its four or five new 

 lice to help on tlie general devastation. 



Such early and rapid breeding im- 

 plies great" nutrition, and we easily 

 understand why tlie plants wither and 

 dry up. We also see how the lice be- 



come so quickly numerous and wide- 

 spread. Calculation shows that in less 

 than a month, if no lice die or were 

 killed, a single louse might be the pro- 

 genitor of more than several million 

 lice. To follow the numbers further 

 defies comprehension. Many have 

 written me: "We cannot imagine 

 where the lice could come from so 

 quickly and rapidly." The above fact 

 explains this physiological riddle. 



'%Vliy !KO :%'uin«rou9 this Year. 



This is not the first season that this 

 avenmhas come like a destroying flood 

 upon the grain fields. In 1861 the lice- 

 swarmed upon the cereal crops of New 

 England and New York, at which time 

 Dr. Asa Fitch fully described it in his- 

 sixth report. In 1866 and again tea 

 years later it did great damage in 

 various sections of the West. We see 

 then that this louse does not come 

 yearly, but only at long intervals. 

 Why is this ? It is doubtless owing in 

 some measure to the weather, but more 

 to its insect enemies. 



We readily see that its enormous 

 prolificness would make it as the sands 

 of the seashore every year, except that 

 soine natural agent held it in check. 

 Fitch describes three such enemies. 

 Even now, as we visit the oat and 

 wheat fields, we find many forms dif- 

 ferent from any previously described. 

 These have short, rounded bodies, 

 which are of a dirty white color. The 

 cause of this is that these are attacked 

 by parasites, which are eating them up. 



We have reared several of these- 

 little benefactors, and find them now 

 busily engaged in the fields laying the 

 eggs that will destroy the lice. These 

 minute parasitic insects lay a great 

 many eggs, one in each louse, and 

 their presence and prosperity mark 

 the doom of the lice. Thus through 

 the agency of these minute parasitic 

 forms, aided by climatic influences, we 

 are to be saved from a raid by this 

 grain aphis next year, and will be 

 greatly benefited this year. Indeed, 

 hi some cases, these little friends will 

 very likely save us from serious damage. 

 Why the parasites are not able to come 

 successfully to the rescue each year is 

 still unknown. Very likely this prob- 

 lem will receive a very valuable prac- 

 tical solution in the future. In these 

 parasites the entomologist sees the 

 doom of the lice, but not, I fear, till 

 great harm is done. 



Drv weather is a great promoter of 

 insect productiveness. It is more than 

 pr<)l)able that the exceeding drouth of 

 1887, 1888, and of the April and May 

 just past, tog<ther with the mild w'in- 

 ter of 1888 and 1889, have had much 

 to do with the i)resent invasion. We 

 mi'dit expect much aid from our fre- 

 quent June rains, but I fear they were 

 too late. 



Observation shows that thi^ 



