394 



DoDD (A. p.). A New Chalcid Parasite of Eitthvrrhimis meditabundiis. 

 — Bull. Ent. Res., London, xii, pt. 1, June" 1921, pp. 67-68. 



Chalcis eulJixryliini. sp. n., bred from Euthyrrhinus meditabundiis in 

 North Oueensiand [see above], is here described. The host record is 

 of interest, as the other members of the genus attack Lepidopterous 

 and Dipterous larvae. 



Davidson (J.). Biological Studies of Aphis rumicis, Linn. — Btdl. 

 Ent. Res., London, xii, pt. 1, Jvme 1921, pt. 81-89, 6 figs. 



Aphis rumicis, L., has many synonyms, owing to its polyphagous 

 habits. A detailed, illustrated description is here given of all the 

 forms of this Aphid. The account of its hfe-history is based on 

 extensive experiments and observations in the field carried on in 1913, 

 1914 [cf. R. A.E., A, ii, 660] and 1920. 



The ova hatch in March and April on the winter food-plant 

 {Eiionymus and probably other genera) and give rise to the fundatrices. 

 These produce parthenogenetic viviparous females, either winged or 

 wingless, or the latter only. They give rise to similar generations, 

 but there is a tendency for the wingless ones to produce a majority 

 of winged individuals. The latter migrate to the intermediate or 

 summer food-plant, and eventually the winter food-plant becomes 

 free from the Aphid. On the summer plants, of which beans are 

 specially favoured, the tendency is for the winged females to produce 

 wingless individuals, and for these to produce similar offspring or a 

 mixed progeny with a varying percentage of winged examples. The 

 liability to overcrowding as the plant becomes heavily infested is 

 thus overcome, and the wider distribution of the species to other plants 

 ensured. 



Towards the end of summer winged viviparous females are produced 

 that are physiologically specialised. These fly back to the winter 

 host and produce sexual oviparous females. About the same tirae 

 winged males are produced from wingless sexuparae on the summer 

 food-plant and fly to the winter one, where the sexual females are 

 fertilised. Eggs are then laid on the winter host, and give rise to the 

 fundatrices in the following spring. 



The remaining wingless forms on the intermediate host gradually 

 die out, owing partly to the tendency to produce winged forms, and 

 partly to unfavourable conditions. Probably during a mild winter 

 agamic forms may survive on certain plants and carry on normal 

 asexual reproduction in the following year. Experimentally a 

 parthenogenetic strain was continued throughout the winter in a 

 greenhouse, winged sexuparae, males, and parthenogenetic wingless 

 females being produced in each generation from September to May. 

 Further, it seems evident from experiments that in the adventures 

 of migration the winged forms of any parthenogenetic generation may 

 alight on the winter food-plant and produce young, resulting eventually 

 in colonies consisting of all stages. Similarly, winged sexuparae 

 alighting on intermediate food-plants may give rise to sexual females, 

 which it is thus possible to find in association both with agamic forms 

 and males. 



