41 



Insects and Vegetable Parasites Injurious to Crops 



The first work undertaken in the laboratories related to this subject, a most 

 important one in the Sudan, and was concerned mth the damage done by the 

 so-called " Asal " (Honey) fly, which has been foxmd to be a large and new Aphides 



..■''■' ^ The "Asal '■«) 



species of Aphis. In 1902 it was very destructive to the dura crop {Sorghum 

 vuhjare) in Kassala, Sennar and the Bahr-el-Ghazal. Last summer, (1903), it 

 was not so much in evidence, but the infection of most of the dura gro-nni 

 in Khartomn gave one an opportunity of studying it on the spot, especially in the 

 Zoological Gardens. I do not think that this latter Aphis is the same species 

 as that found on samples sent from Kassala and Sennar. These were very dry and 

 shrivelled, and only a few good specimens were secured. They seemed to be 

 larger than the Khartoum Aphides and had red eyes, whereas those of the 



Khartoiun species wei^e black. The 

 eggs were also different. In Khar- 

 tomn there was not nearly so copious 

 a secretion of honey-dew, though 

 the leaves were rendered sticky. 

 Differences were also noted in shape. 

 The life history of the Aphides is 

 very complicated, oAving to the 

 ciu'ious alternation of generations, 

 and unless one be an economic 

 entomologist it is not easy to trace 

 out the various stages and recognise 

 the sexes in the winged and wingless 

 forms. Possibly one stage of the 

 insect's hfe is spent on the melon 

 l)lant. I have had melon plants sent The melon 

 from Rufaa on the Blue Nile with ^^ '^ 

 the leaves covered by the Aphis 

 secretion, Avhich often retained the 

 shape of the excreting cornicles and 

 presented a beautiful appearance 

 when viewed through a magnifs'ing 

 lens. These leaves were completely 

 blighted and the melon crop was 

 ruined. It is, however, probable that this Aphis is yet another species, (for 

 one thing the larva^ are very large), and that the others confine their 

 attentions to the dui'a. They certainly do much damage, sucking out the sap 



Leaf of Sorghum vulgare, intt-stL-d by the Aphis sorghi. 



