336 



Janata (A. A.)- AonOJlHCHifl K"b Sionorm SyKapKM. [Additional data 

 on the biology of Rhynchites 'pauxillus, Germ.] — •«Tpyflbl 



EcTecTBeHHo-McTopMHecKaro Myaen TaBpMMecKaro FyOepHCKaro 



3eiKICTBa.» — \^Memoirs of the Natural History Museum of the 



Zemstvo of the Govt, of Taurida], Simferopol, iii, 1914, pp. 79-98. 



This article gives the results of observations on the biology of 



Rhynchites pauxillus, Germ., conducted during 1912 and 1913, and 



forms a continuation of previous work on the same subject. With 



regard to the diapuse of the larvae, three series of experiments are 



described and summarised as follows : — The larvae only emerge from 



the leaves when these are destroyed by decomposition, and thus free 



them. The decomposition of the leaves is hastened by the amount of 



moisture, and therefore by accelerating decomposition the larvae 



may be made to issue sooner. Until the exit from the leaves the 



further development of the larvae is delayed and a state of diapuse 



arises. The larvae, which have passed from the leaves into the earth, 



remain in a state of diapuse, if the time of their exit is earlier than 



the normal one for pupation (in one experiment the larvae passed 



into the earth in April 1912, and remained there without pupating 



for four months). Generally speaking, the larvae remaining in a state 



of diapuse attempt to pupate and continue their metamorphosis at 



the normal times — viz., pupation at the end of summer and emergence 



of the imago in the autumn. The larvae from non-decomposed leaves, 



not subjected to moisture, are unable to get out of the leaves, being 



evidently unable to overcome with their mandibles the resistance of 



the undecomposed epidermis. This delays their development. If the 



leaves are moist, but not to such a degree as would result in 



decomposition, the larvae may remain in a state of diapuse for two 



years and more. Under conditions which produce the rapid and 



complete drying up of the leaves the larvae perish. The duration of 



the life of the larvae in the state of diapuse depends on the kind of 



tree, and they perished earlier in apple leaves than in those of pear, 



as the latter, owing to their impermeable cuticle, dry up more slowly. 



In Nature the state of diapuse has no need to last so long as under 



the artificial experimental conditions, and the ability of the larvae 



to remain in that state much longer than is required by the natural 



conditions of the Crimea tends to show that this adaptiveness has been 



acquired in some other country with longer dry seasons. Observations 



show that the parasite, Bracon discoideus, Wesm., winters in cocoons 



in the pupal stage, amidst fallen leaves, on or in the earth. The whole 



cycle of the development of the parasite is as follows : — The wintering 



generation appears at the end of May and oviposits in the first half 



of June ; its larvae and pupae are found in the middle of June, and 



a second generation appears at the end of that month. The larvae 



and pupae of that generation are found in the first half of July, and 



the majority of them remain over the winter ; a minority produces 



a third generation which is on the wing and oviposits in the middle 



of July, the larvae appearing at the end of that month and the pupae, 



which are found in the first half of August, remaining over the winter. 



In 1912 the author observed in one orchard near Simferopol a great 



mortality of the larvae of R. pauxillus, owing to the attacks of aphids 



on the leaves in which they were enclosed. The sucking of the leaves 



by the aphids deprived the larvae of their food, and both on apple 



and pear trees they perished in swarms. 



