1887.] Phylloxera Vastatrix at the Cape. 5^ 



I have conclusively shown that it has "here no checking influence on 

 the insect. That does not invalidate the theory of recent introduction 

 because it is well known that insects are not so affected by heat as 

 they are by cold. 



If we take into consideration the small duration of cold weather 

 experienced on the coast districts, we may conclude that this short 

 period of rest is nothing when compared with the immense advantage 

 the insect derives from the favourable circumstance of a hot and dry 

 climate. Every observer in France had to arrive at a similar 

 conclusion , 



Dr. Cornu found that with the temperature varying between 86° 

 and 95° Fahr. (30° to 35° 0.) the young hibernant had laid its first 

 e^^ in twelve days. This gives three days for each shedding of skin. 

 This result corroborates the observation of the late Mons. Lichten- 

 stein. This observer found. that a constant temperature of about 

 76° Fahr. (25° 0.) would allow the development of the winged form 

 in eighty to ninety days. 



I have been able to obtain the same result here, as will be seen 

 hereafter. 



From the foregoing remarks it will be seen that the danger of dis- 

 semination of the insect from May to September, while I was unable 

 to do anything against it for want of a disinfecting agent, has been 

 greatly lessened, and also that the application of Bisulphide of Carbon 

 should be made early in September. 



AERIAL FORM. 



The spreading of the phylloxera takes place mostly in the ground. 

 It has also been found walking on the soil, but the contamination at 

 great distances is due mainly to the winged form. 



For a long time the winged form was considered as very rare. But 

 the observations of Dr. Cornu have shown that it was purely due to 

 the fact that it was looked for where it does not easily develope, and 

 that the nymphs, which ultimately become winged females, are not to 

 be found generally on the roots, but on the swellings of the rootlets. 



These rootlets being of course more numerous on healthy vines, it 

 follows that in a contaminated vineyard the winged female will be 

 produced in large numbers during the first year of infection. 



But the rootlets wither generally towards the end of summer, and the 

 nymph, owing to the difiiculty of getting more nodosities (as when 

 attacked the rootlet soon rots, and the death is accelerated by the 

 number of phylloxera which derive their sustenance from it) gets 

 probably at that time near the surface of the soil, and there, after 

 a last shedding of skin, emerges as a winged form. 



On the ground of these observations, the Commission was led to 

 expect to get the winged form late in the year, although numerous 

 nymphs had been met with everywhere. 



Two vines, six months old, well stocked with insects, were deposited 

 in the laboratory. They came from Mr.* Kotze's vineyard at Mow- 

 bray, and were planted in the original compact argillaceous soil. 



On the 23rd of April only I obtained the first winged insect ; the 

 exodus continued until the 5th of May, and then ceased ; a copious 

 watering of the plants after the first exodus having seemingly 

 increased it. The exodus coincided with the appearance in the open 

 ^ir of numerous other winged forms of Aphidce, 



