10 



several seasons, the tobacco will always be liable to attack. It 

 may be mentioned that when the grubs are present in great 

 numbers in the soil, they are very manifest during ploughing 

 operations, and much good would doubtless result from the use 

 of " boys " to collect and destroy them as they are brought to 

 the surface. If the numbers are seen to be very great, how- 

 ever, the wisest course, if practicable, would doubtless be not to 

 plant tobacco on that piece of land. 



KOOT GALLWORM (Heterodera radicicola) . This is an 

 important and dangerous pest which at the present time occurs 

 very rarely in tobacco lands in Southern Khodesia. It is, how- 

 ever, prevalent in several parts of the country in land that has 

 been used for potatoes, and is likely to be introduced into- 

 tobacco lands if growers are ignorant of its dangerous nature, 

 and the facility with which it may be transported, 'especially 

 through the medium of infested seed potatoes. 



The pest, and the injuries caused by it, are illustrated in 

 the adjoining plate. The eggs are hatched within the swollen 

 body of the female, who gives up her life in the process of repro- 

 duction. The young worms, shewn in the plate very greatly 

 enlarged, are threadlike and provided at the anterior end with 

 a spear-like instrument, which can be thrust out of the mouth 

 opening and withdrawn. The newly-hatched worm is, of 

 course, exceedingly minute, and not to be distinguished by the 

 unaided eye. After wandering about on the plant tissues for 

 some time, it comes to rest, and finally changes to an adult. 

 The adult males remain slender,, and measure about a twenty- 

 fifth of an inch in length. The females swell up, and assume 

 the shape shewn in the illustration. They become distended: 

 with eggs that hatch within their bodies. 



Migration from plant to plant in the field is effected 

 through the activity of the young worms, which may either 

 voluntarily leave their host plant to seek a new home, or may 

 be released into the soil by the decay and breaking away of the 

 infested tissues of the plant. The young worms make their way 

 into the rootlet of a new plant, by means of the piercing organ 

 with which they are provided. In travelling from plant ta 

 plant, they seem to be much assisted by a soil of a sandy charac- 

 ter, and it is usually such soils which become badly infested 

 with the pest. As they are fond of damp ground, it is likely 

 that many of the wet vleis of granite sand in different parts of 



