A HISTORY OF DEVONSHIRE 



GALL MAKERS 



The life histories of the gall-makers arc the best known of the Cynipidae group, and the majority 

 are found on the oak. The cycle of life of nearly all the gall-makers has been carefully and ably 

 worked our by Drs. Mayr and Adler, and their observations confirmed by others. 



The oak gall-flies are very remarkable in having an alternation of generations, i.e. the 

 autumnal galls are all females, reproducing their species without the assistance of the male. 

 Nearly the whole of the galls observed on oak trees in spring or early summer produce males and 

 females. Another great feature is that each generation is never like that which it proceeded from, 

 but always like its grandparents. In two instances, the winged sexes produce apterous 

 (wingless) generations, all of which are females. These deposit their eggs and produce winged 

 males and females. The galls of the two generations are never alike in any way, nor are the 

 flies, in size, form, or colour. The spring generation is often three times smaller than its parent. 

 The spring galls, as a rule, from the time the egg is deposited to the appearance of the flies, are 

 within six months, while many of the autumnal galls do not produce flies until the third, and 

 sometimes the fourth year. 



Oak gall-flies are not alone in being able to reproduce their species by virgin females. 

 Dr. Adler has proved that the bedeguar-rose or robin's-pincushion gall fly {Rhodites rosae) is able to 

 continue her race without being fertilized, and no doubt several others are able to do the same. 

 Among the saw-flies {Tenthredinidae) several cases have been known by experiment, one virgin 

 female producing all males, another species all females, while a third would produce males and 

 females. 



Among the oak gall-flies there are several whose bisexual form is not known, if we presume 

 that there is one, for instance that of the common marble gall {Cynips Kollari), which is so con- 

 spicuous in winter, when the trees arc leafless. All these galls produce female flies, and all efforts to 

 produce flies in confinement from these females have so far been fruitless. The writer has tried 

 during the past thirty years to accomplish this object by placing flies on oaks of all ages, from one 

 year old, up to branches on trees of sixty years. All these experiments were made by placing the 

 several young trees or branches under a muslin frame to prevent the escape of the flies and to 

 exclude intruders. Cynips Kollari is not the only oak gall-fly that is supposed to be parthenogenetic. 

 Dr. Adler says that he has bred Andricus albopunctata from flies of albopunctata. These flies are 

 always females, consequently parthenogenetic reproduction appears to be proved in the case of 

 A. albopunctata. 



Andricus solitarius, glandulae, quadrilineatus, seminationis, Dryophanta agama, and disticha all produce 

 females only ; parthenogenesis may exist with all of them. The writer is not of that opinion. 

 Take the case of glandulae. The gall is found commonly in October ; the gall-fly emerges in April. 

 The question is, how is the time passed from April to August orSeptember ? Dr. Adler says ' Embry- 

 onic development begins immediately after the egg is laid ; absolute rest in the evolution of the egg 

 never occurs, for even if the temperature should be very low, the formation of the blastoderm begins 

 at once. Naturally this proceeds more slowly in a cold than in a warm season.' Consequently 

 there must be a connecting link to keep up the continuity of this species. 



It was at one time supposed that the marble-gall was produced at the expense of the acorn. 

 Botanists well know that the fruit-producing flowers appear on the oak in April, at the same time as 

 the catkins ; consequently after the female flower is fertilized, the future acorn very gradually 

 commences its growth ; in fact, the embryo acorn is not seen until after the fourth or fifth leaf 

 is produced. The eggs producing Kollari galls are not deposited on buds of old wood, but on 

 twigs that have grown some time after the growth of the acorn commenced ; or, in other words, 

 the female flowers were produced, fertilized, and the acorn started on its journey of life, while 

 the twig which the parent of Kollari gall would be likely to select to deposit her eggs was still 

 within the bud. 



It is only within the last two years that the writer has had an opportunity to experiment 

 with gall-flies that have not a known bisexual form, to try if the flowering buds would prove the 

 condition the flies required ; the experiment so far has certainly proved a failure. 



Unfortunately some of these gall-flies do not emerge until the third year, and require during 

 that period much attention. They must not be kept in the sun or allowed to get too dry, and 

 must be exposed to all weathers. 



The inquilines or lodgers {Synergi) are more often parasites than they are generally supposed 

 to be. One hundred Cynips Kollari galls gathered in March and April, 1901, produced only 

 eighteen gall-makers, 495 Synergus Reinhardi, forty-seven S. melanopus, and fifteen Chalcids. Only 

 one gall produced the maker and inquiline. 



Of the following list of oak gall-flies all, with one exception, Andricus agama^ have been 

 obtamed in the valley of the Plym. 



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