Where this Year's Insects Came From— By e. p. Felt, 



New York 



State Entomologist 



THE CAUSES THAT CULMINATED IN THE EXTRAORDINARY ONSLAUGHT OF PLANT LICE DURING 

 THE PAST SUMMER — THE SIGNIFICANCE OF THE APPEARANCE AND ITS PROBABLE CONSEQUENCE 



MULTITUDES of plant lice were to 

 be found recently on the foliage 

 of many trees, shrubs and other plants. 

 The abundance of these small insects was 

 most remarkable and is comparable only 

 with the outbreaks of 1897 and 1903, years 

 distinguished by the superabundance of 

 plant lice. Observation and weather records 

 show a correlation between temperature and 

 the multiplication of aphids. The present 

 season was remarkably cool and backward, 

 a marked change for the better occuring June 

 21st. The earlier cool weather was favor- 

 able to the plant lice, while the more recent 

 warm weather permitted their natural 

 enemies, such as lady beetles, flower flies 

 and minute four-winged parasites to multiply 

 and perform a most important function in 

 checking the hosts of destructive aphids. 



Similar climatic conditions prevailed in 

 New York State during the outbreaks of 

 six and twelve years ago. Recent obser 

 vations on the spring grain aphis in the 

 Southern and Middle states have shown 

 a correlation between temperature 

 and the development of plant lice 

 and their enemies. 



Furthermore, experiments 

 have demonstrated, in the 

 case of this species, the futility 

 of large importations of para- 

 sites in the expectation of 

 hastening its subjugation. 



It should not be assumed 

 from the above that tempera- 

 ture is the only factor con 

 trolling insect outbreaks — such 

 is far from the case. The recent 

 extensive defoliations of forest 

 and shade trees by leaf-eating 

 caterpillars of various species 

 are, in the majority of cases, due 

 to the relative paucity of natural 

 checks, such as insect enemies 

 and particularly insectivor- 

 ous birds. The reckless 

 and criminal slaughter of the 

 recent years has already begun 

 its effect in disturbing the balance of 

 Nature. Army worms are controlled mostly 

 by parasites, while their abundance may be 

 demonstrated by such a relatively slight 

 factor as a hail storm destroying a portion 

 of the feed in an infested area and producing 

 later the familiar marching caused by a 

 scarcity of provender. 



The variations in numbers of May or 

 June beetles and their destructive grubs in 

 grass land is due in part to the fact that 

 three years are required to complete the life 

 story, hence the more or less triennial 

 character of these visitations. Rose beetles, 

 frequently abundant in widely separated 

 localities, appear to be influenced only 

 slightly by weather conditions, the size of 

 swarms being controlled mostly by the 



proximity of large, sandy areas in grass, 

 the preferred habitat of this devastating 

 beetle. Other factors are also important in 

 determining the abundance of insects. 



It would be extremely hazardous to ven- 

 ture a prediction as to what pest might be 

 troublesome another year, though it is 

 safe to add that were either the brown 

 tail moth or the gipsy moth of Mass- 

 achusetts to become abundant in a locality, 

 the residents would be more than satisfied 

 to have the scourge abated. 



Plant lice, des- 

 pite their 

 overrun- 



atter in 

 to have 



of attacks by a plant louse 



vegetation and the abundance of sticky 

 honeydew so frequently present, are extremely 

 interesting. There are something like 325 

 species occuring in America, each exhibiting 

 peculiarities in habits and structure. A plant 

 louse may be defined as little more than an 

 animated egg-producing sack, expressly 

 designed by Nature for rapid multiplication. 

 The fecundity of certain species is appalling, 

 since only eight days are necessary for the pro- 

 duction of one generation. Professor Riley, 

 some years ago, estimated that the descen- 

 dants of but one hop plant louse in one season, 

 under favorable conditions, might be suffi- 

 cient to blight hundreds of acres within two 

 or three months. 



Plant lice are small, many being about 

 one-tenth of an inch long. They are easily 

 recognized by the somewhat swollen, sack- 

 like body and the slender feelers or antennae, 



frequently as long as the body and just 

 above the conspicuous eyes. Four mem- 

 branous wings may or may not be present. 

 Most characteristic of all is a pair of con- 

 spicuous honey tubes near the posterior 

 extremity of the body. These insects exhibit, 

 among their various species, a large variety 

 of colors. 



Plant lice are practically helpless of them- 

 selves, so far as protection from natural 

 enemies is concerned, and depend in large 

 part upon their wonderful fecundity. They 

 have important protectors in ants which 

 profit by feeding upon the sweetish honey- 

 dew produced by the aphids. Some ants 

 even go so far as to colonize plant lice 

 on the roots of grasses and care for 

 them as carefully as a farmer pro- 

 tects his milch cows. 



A number of species of plant 

 lice have forced themselves upon 

 the attention of the public dur- 

 ing this season. A very pretty 

 form, dressed in a gay livery 

 of red, white and black is 

 known as the painted maple 

 leaf aphis and is sometimes 

 quite injurious to the foliage 

 of soft maples in particular. 

 One of the most common 

 and abundant is the rosy 

 apple aphis, a pale rosy- 

 greenish form, frequently so 

 abundant as to curl most of 

 the more tender leaves on 

 young apple trees at least, and 

 seriously affect the foliage on older 

 trees. Two other species are occa- 

 sionally associated with this destruc- 

 tive form. The woolly apple aphis 

 usually forms patches of white on 

 the trunks. and branches, partic- 

 ularly around scars and wounds 

 and is responsible for ugly defor- 

 mations of the roots. Plum has 

 been badly affected by a greenish 

 plant louse, while the exceedingly destruc- 

 tive black cherry aphis has been more than 

 usually abundant, blasting many of the more 

 tender leaves. Elms and maples have been 

 levied upon so freely by these animated 

 pumps that the foliage and even the ground 

 beneath has been kept wet and sticky by the 

 copious excretions. This honeydew is liable 

 to become infected by a sooty fungus and 

 then the besmeared foliage becomes very 

 unsightly. 



The relations between plant lice and their 

 food plants are by no means simple. The 

 hop aphis, so destructive to hop yards in 

 many sections of the country, winters on the 

 plum and passes several generations on that 

 tree before forsaking it in June for the hop, 

 where it may produce four to twelve gener- 

 ations before returning to the plum. A most 

 interesting plant louse produces an oval. 



