Insects galls of Springfield, Massachusetts, and vicinity
Bulletin 2: Springfield Museum. development of a large number of galls upon a plant is injurious to that plant is evidenced by the effect of the grape phylloxera, Phylloxera vitifoliae, generally known as Phylloxera vastatrix. In the eastern United States, where it is native, little injury results, but when it was carried to France it multiplied to such extent as to cause very great loss in the vineyards through which it spread. This is an illustration of the the greater damage done by a pest
... a new habitat. Some galls are so noticeable that they have attracted attention from earliest times, but it was not until 1686 that any systematic work was published upon the subject, when Malpighi issued "De gallis," which gave descriptions of those known in Sicily and Italy. Among modern P^uropean writers Adler's name is especially noteworthy because he established the theory" advanced by Bassett, of the alternation of generations among certain of the Cynipidae. Bassett was able to verify his thought in one ease, while Adler worked out a series of cases, but found that alternation of generations was not universal among Cynipidae, as Bassett had thought probable. Howard, in Psyche, 1882, v. 3, p. 329, says: -"America may justly claim the credit for the discovery of this most interesting fact of alternation of generations among cynipids." Continuing, he says of Bassett : "With Cynips q. operator he had observed the females of the vernal brood ovipositing in acorn cups and producing the gall q. operatola of Riley's MS. ; but he failed to rear the flies from these galls and so missed the complete proof. In the case of C. q. batatus Bass., he had bred the sexual forms from leaf galls, and the agamic females from twig galls ; but had not actually observed the females of the former in the act of ovipositing in the twigs, thus again missing the proof. Riley, however, as he tells us in his published note, succeeded in breeding the agamic females of q. operator from the acorn galls, thus, in connection with Bassett's observation of the oviposition, completely establishing the fact of alternation. So the credit should be joint." Much was contributed to our knowledge of galls by Osten Sacken, Bassett, Fitch, Harris, Shinier, Riley and Walsh among the earlier workers in America. While several names should be noted among recent workers, Pergande, by patient observation of the gall-makers upon the witch hazel, has disclosed the identity of two sets of insects previously supposed to be four species, and established the fact of their migration from one host-plant to another and back again. And Cook has given us the results of careful study of the abnormal development of the plant tissues and their cellchanges under the stimulus of the gall maker. Galls have been collected in this section which owe their origin to six orders : Acarina (Family, Eriophyidae). Insect Galls. 5 Hemiptera (Families, Aphididae, Psyllidae). Coleoptera (Family, Cerambycidae) . (For a more complete list of the species under each family mentioned above see the list serving as index of the gall-insects near the end of this Bulletin.) In general the more highly organized insect produces the more complex gall. There may be apparent exceptions to this rule, as in the case of the bark louse, Adelges abietis, producing a gall at the base of needles of the spruce which is very similar to one produced on the needles of the pitch pine by a two-winged fly, Diplosis pini-rigidae. Order, ACARINA. Family, Eriophyidae, Gall-mites. These mites are of minute size, and are to be found among the hairs or grains with which the concave surface of the gall is lined. There are several generations during the summer, the newly hatched mites movingout over the plant and producing new galls. The adults hibernate under the scales of buds or in crevices in the bark. A few species are found in such numbers on the leaves of cultivated fruit trees or shrubs as to cause much damage, the aborted leaves not being able to provide sufficient food for the development of the fruit. The galls are usually very simple in structure, and always have an opening by which the maker can pass out°r in * Order, HEMIPTERA. Family, Aphididae, Plant-lice. These insects are soft-bodied, with sucking mouth-parts. There are winged and wingless forms, the latter reproducing parthenogenetically. There are several generations in a season. The galls are usually quite simple in structure and contain many insects. There is an opening for their egress, altho in a few cases this remains closed until the gall matures and dries slightly. Family, Psyllidae. These are much like the aphids, but have hind legs fitted for jumping. The galls are similar in general structure, altho possibly a little more complex. Order, COLEOPTERA. Family, Cerambycidae, Longicorn beetles. Most cerambycid larvae are borers in the wood of trees and shrubs, a few in herbaceous plants, but the larvae of a few species produce galls. Order, DIPTERA. Family, Agromyzidae. The production of galls b} 7 the larvae of agromyzids is very exceptional ; most of these larvae mine in the leaves or stems of plants. 6 Bulletin 2: Springfield Museum. Family, Trypetidae. These flies are most of them nearly as large as a house-fly. There are few that produce galls. The galls are comparatively complex. Family, Cecidomyidae, Gall-gnats. These are small two-winged flies which are seldom noticed. The eggs are laid on a surface of the plant. The larvae either feed from the surface, making an open gall, or gnaw into the tissues of the plant, making a closed gall which opens on maturity at the place where the larva entered, altho during the growth no opening may be evident. The larvae can generally be identified by the color, yellow, orange, or reddish, and by the structure of an organ near the anterior end, which has been designated the 1 'breast-plate" or "breast-bone." These gall-makers are numerous both in species and individuals. Their galls are sometimes quite complex in structure. Order, LEPIDOPTERA. Families, Tineidae, Elachistidae, Gelechiidae, Tortricidae. The adults are very small moths. There are very few gall makers among them. The eggs are laid on the surface of the plant, the larvae enter the tissues and either leave an opening, as in the gall of Ecdytolopha insiticiana on the locust, or just before pupation gnaw almost through the wall, leaving a place for the emergence of the adult, which, of course, having no organs for boring or biting, could not otherwise escape. Order, HYMENOPTERA. Family, Tenthredinidae, Saw-flies. The members of this and the following family are four-winged insects. The adult tenthredinid is distinguished by the structure of the ovipositor, which consist of several toothed blades, by which the insect cuts or saws into the plant tissue, and there deposits the eggs. Whether a gall-maker deposits also some irritating liquid which causes the gall is a much discussed question. However that may be, it is true that the only cases so far directly observed in which a gall is formed before or without the hatching of the egg have been in this family, among the Nemaiinae. The larvae somewhat resemble caterpillars. Several species make galls on willows. Family, Cynipidae, Gall-wasps. In the adult the abdomen is usually compressed. The ovipositor is long and slender, and can well bury the egg within the plant-tissue, leaving no mark. The larvae pupate in the closed gall, and the insects when mature cut their way out of it. Alternation of generations is one of the most interesting features in the life of these highest of gall-makers. The galls are, without exception, complex in structure, with several distinct divisions of the walls, and many interesting adaptations for the protection of the inmate. Insect Galls. 7 Within galls may sometimes be found parasites or inquilines. The former, preying directly upon the gall-maker, causes its death, but not until its growth is nearly or quite complete. The inquilines are merely guests within the gall, profiting by the food supply and by the protection. Aside from the collection of the galls of different localities, and the subsequent summary of their distribution, two very interesting questions suggest themselves for investigation. First, are these malformations the result of chemical or of mechanical action? Second, of which of the American gall-makers is it true that there is alternation of generations? The classification of gall-insects will undoubtedly be somewhat altered when this question is answered. Either line suggests a fascinating series of observations and experiments for the one undertaking it. My thanks are especially due to George Dimmock, Ph. D., for suggestions in preparing this paper, for use of publications not otherwise available and for reading the manuscript.