BULLETIN 198. THE GRAPE LEAF-HOPPER. 191 



fairly well in a photograph, but not distinct enough to reproduce here. 

 Upon examining these eggs that failed to hatch they appeared not to 

 have started their course of development, or in other words, were 

 infertile. The egg itself was generally found to be fresh and intact, 

 the black color on the leaf being due in most cases entirely to the 

 epidermis over the egg. This was in a vineyard where the hoppers 

 appeared in innumerable numbers in the early spring, and the eggs laid 

 were from hoppers that had remained over winter. The mortality in 

 the egg stage reduced their numbers to a very appreciable extent. 

 What was true of this one vineyard in 1907 was observed very generally 

 in the vineyards around Lodi in 1908. 



We tried to account for this failure of the eggs to mature from a 

 number of causes, but the matter is still unsatisfactorily settled. We 

 first started on the supposition that something in the nature or make-up 

 of the leaf, or a bacterial or fungous disease of the egg, might be 

 responsible. The underside of the leaves of these vines were covered 

 over more or less with pubescence or hairs. That this might have 

 some effect in a mechanical way by holding moisture and thus fur- 

 nishing the best conditions for producing disease was not borne out, 

 since the same conditions were noted elsewhere with practically no 

 mortality. The hoppers themselves seemed to be as healthy as those 

 elsewhere, and a miscroscopical examination showed nothing unusual. 

 That the eggs were infertile seems evident, but the exact cause in this 

 particular area is not yet accounted for. Males were present in their 

 normal numbers, and our experiments thus far indicate that they do 

 not reproduce parthenogetically. 



The exact causes of such conditions as these will largely account for 

 the sudden disappearance of the hoppers after having become very 

 abundant. It is well known that hoppers, like many other insects, 

 have their ups and downs as regards numbers. In 1897 the hoppers 

 were so abundant about Fresno during the winter that the people 

 appealed to the University for aid in combating them for the approach- 

 ing season. An investigation was undertaken by Professor Woodworth 

 and headquarters opened for a season's campaign ; the hoppers appeared 

 in great numbers in the spring, as was to be expected from their 

 abundance in winter, but the majority failed to lay eggs and none 

 appeared to be normally productive, and as a result there were scarcely 

 enough of the new generation produced to furnish good material for the 

 investigation. From what is known of the history of the pest in the 

 State, this is an example of what occurs more or less periodically. 



Effect of Oviposition on the Leaf. So far as we could see the 

 puncturing of the leaf tissues for egg laying had no appreciable effect 

 on the functions of the leaf. In many cases it was hard to tell where 



