31 



holdings the Eclair, or other similar Knapsack machines, may 

 be used. 



In the case of large cabbages, among which it would be diffi- 

 cult to move a machine, Knapsack machines would be more 

 convenient. It would be necessary to apply the wash all over 

 these plants. 



Powdered applications have not been found so efficacious as 

 washes, and rather, perhaps, that it has been difficult to throw them 

 up under the turnip leaves, where the aphides congregate. But 

 the Strawsonizer, as was proved in the Diamond-back moth 

 experiments carried out by the Board of Agriculture in 1891, 

 has been arranged so as to thoroughly cover every particle of 

 the under surfaces with dry substances. Soot and lime, mixed 

 in the proportion of one part of lime to three of soot form the 

 best remedy of this nature. Very small quantities can be put on by 

 the adapted Strawsonizer, and such were found sufficient to rout 

 the caterpillars of the Diamond-back moth, as they were blown 

 up with great force. 



It is clear that the main attack of these aphides comes 

 from cruciferous weeds, which retain the eggs during the winter, 

 or harbour the wingless viviparous females and furnish them 

 with food in the early spring, nourishing them until the culti- 

 vated plants are ready for them. Therefore, charlock, penny 

 cress, the wild radish, shepherd's purse, and 'other cruciferous 

 weeds, should be kept from fields and their outsides as much as 

 possible. Charlock and other weeds of this order are frequently 

 found in clover leys. They are dangerous sources of mischief, 

 and should be brushed off close in the autumn. It must be 

 remembered that- a few females can blight whole districts. 

 Reaumur has calculated that one aphis can be the progenetrix 

 of 5,904,900,000 aphides during its life. 



There are several enemies of the Aphis brassicce, which, in 

 some seasons, greatly diminish its numbers. Among these are 

 Lady-birds, Coccinellce, whose black larvse, known as " niggers " 

 in the hop districts, clear them off by wholesale. The voracious 

 larvae of at least two species of Syrphus flies devour quantities 

 in incredibly quick time ; and parasitic flies of three species lay 

 eggs in the bodies of the aphis larva?, to their utter destruction. 

 Chief among these is an Ichneumon fly, named Trionyx rapcv, a 

 pretty dark brown insect, with yellow rings round the lower part 

 of its body. It has a wing expanse of nearly the fourth of an 

 inch, and its body is not quite the sixth of an inch long. 



