285 



wa.tcr, alcohol 70 per cent., nicotine 1 per cent, aq., acetone, ether, 

 cJiloral hydrate aq., water. The net result of these experiments goes 

 to show that a much greater range of liqiiids than are generally used 

 have a toxic action, and it is probable that the structure of the spiracles 

 and tracheal system is a far more important factor than is generally 

 supposed. It would almost appear that most insects can only be 

 reached with an insecticide through the spiracles, and that an 

 insecticide which does not actually fill the spiracles is not active. This 

 possibly explains the common failure of contact poisons against larg3 

 insects. It is suggested that a careful stady of the tracheal system 

 of each insect should be made, then of the wetting action of the 

 insecticide on the plant, thirdly of the wetting action on the insect, 

 and fourthly of the suitable toxic ingredient to be added to the 

 insecticide. This offers a large field for what the author regards as 

 very necessary research. What is wanted is a reason for the method 

 adopted, and at present this is often deplorably lacking. 



Hargreaves (E.). The Life-History and Habits of the Greenhouse 

 White Fly [Aleyrode^s vapor arionim, Westd.) — Ann. App. Biol, 

 London, i, nos. 3 & 4, January 1915, pp. 303-334, 56 figs. 



Aleurodes vaporariorum has a wide range of food-plants ; it prefers 

 potatoes, and such greenhouse plants as tomato, cucumber, melon, 

 heliotrope, lantana, and salvia. The flies and larvae occur in such 

 immense nimibers that the plants become impoverished, and the quantity 

 and quality of such fruit as tomatoes and cucumbers are affected. 

 The whole of the under-side of the leaves is often completely covered 

 with the scale-like larvae and pupae. These produce a large amount 

 of excreta (honeydew), which fall on to the leaves below, encouraging 

 the growth of fungi that ruin plants used for ornamental purposes. 

 The adults prefer the young leaves for oviposition, and gradually 

 ascend as the plant grows ; hence there will be all stages of the life- 

 history on different levels of the plant ; adults will be emerging on 

 the oldest leaves. Occasionally eggs are laid on the stalks, flowers, and 

 upper leaf-surface, but they are generally laid in circles on the under-side, 

 if the leaves are not very hairy and the insects undisturbed. The mode 

 of oviposition and the changes of colour of the egg, which generally 

 hatches from 10 to 13 days after deposition, are described, as well as 

 the mechanism of hatching. The greater part of this paper deals in 

 great detail with all stages of the Ufe-history. The first instar lasts about 

 1 1 days, the second about 18, the third instar, which is also inactive, 

 varied from 5 to 36 days. The pupal stage (fourth in.star) varied 

 in duration from 21 to 59 days. The longest duration of the fifth 

 (imago) instar was 38 days. 



The author placed three females, isolated before complete emergence 

 so as to be certain that they had not been fertilised, each on a clean 

 plant. From these he obtained ten, thirteen and twenty imagines, 

 respectively, all females. From these he got females again, and of the 

 hundreds of flies examined did not encounter a shigle male. Morrill, 

 writing on parthenogenesis in the Aleurodidae, states that unfertihsed 

 eggs hatch, giving larvae resulting in male flies, and suggests that the 

 fertilised eggs will all give rise to females, as in bees. Morrill and Back 

 further estabhshed parthenogenesis in Aleurodes citri. 



