The Tobacco Slug. ^f) 



Effect of Drought, 



According to certain reports, the pest is greatly favoured in 

 Piet Retief by wet weather, and during dry spells it is said to do 

 little damage. It was also observed at Umkomaas by Mr. R. H. 

 Harris that over moist soil the pest was much worse than on dry. 

 The explanation at the latter place might liaA^e been that ants were 

 numerous on the dry soil but not wliere the ground was wet. In 

 the laboratory at Durban there was no greater mortality of the slugs 

 during hot dry weather than at other times ; but heat and evaporation 

 are greater in the open than under a roof; and it is drier in most 

 inland tobacco areas than at Durban. There remains a hope that 

 the pest will not thrive in the drier parts of the country. 



Natural Enemies. 



The insect being an introduced species and the larva being pro- 

 tected by an offensive excretion and the beetle by an offensive smell, 

 probably accounts for the small number of natural enemies which as 

 yet have been observed attacking it; but it belongs to a genus which 

 is well represented in South Africa, and it is therefore likely that 

 we shall find native parasites taking to it in increasing numbers. 

 However, they may never keep it down sufficiently to make control 

 measures unnecessary. 



The most effective enemy observed is the '' Bighead " ant 

 {Pheidole punctulata), and in Durban no infestation by larvae of 

 the insect lias been found on dry friable soils, whicli this ant seems 

 to prefer. Larvae put amongst these ants were soon destroyed. 

 Another ant, Myrinecaria eumenoides, has also been found to carry 

 off the slugs, but not so readily as P. punctulata, and it may not be 

 an effective enemy. The coramoii " Malmier " (Plagiolepis custo- 

 diens) is apparently useless against the pest. Sometimes one of these 

 ants has been seen to touch a slug, but to recoil from it with actions 

 expressive of the utmost disgust. Other ants, no doubt, will attack 

 the pest; but the question whether ants can be profitably encouraged 

 in tobacco fields has not been in A^esti gated. 



At Piet Petief, and also near Durban, assassin (Reduviid) bugs 

 of different species have been seen attacking both beetles and slugs. 

 A spider was once observed carrying off' a young larva, and at another 

 time a spider got into a breeding jar, and was found spinning up a 

 beetle. Droppings of a bird were seen with what appeared to be 

 elytra of this beetle, and an aphis lion has been observed attacking 

 the larva. Chickens and turkeys are reported to feed on the slugs, 

 and may prove useful in keeping the pest down. Cocoons exposed 

 outside to attract possible parasites were found eaten out, apparently 

 by a rat or a mouse. 



Control Measures. 



Though many experiments have not yet been carried out on the 

 control of this insect, it is considered sufficiently proved that it can 

 be kept down successfully. 



Hand-crushing. — The crop at the Piet Eetief Experiment 

 Station was kept free this year entirely by hand-crushing. This 

 method is expensive ; but that it can be effective is shown by the fact 

 that the shoots which sprung from the stumps, though not attended 

 to, grew up uninjured. This would seem to show that thorough con- 

 trol early in the season may prevent later trouble, providing there 



