34 SHADE IN COFFEE CULTURE. 



attained to full growth, but according to Dr. Edward Palmer this is 

 accomplished by a process of gradual thinning. 



SHADE AND THE COFFEE LEAF-MINER. 



The coffee leaf -miner, Cemiostoma coffeellum, the larva of a small lepi- 

 dopterous insect related to the clothes-moth, has appeared to furnish 

 an argument for the direct benefit of shade, but observations recently 

 made in Porto Rico seem to indicate that this question may be prop- 

 erly discussed among the effects of unwonted exposure. 



The leaf -miner burrows in the middle layer or soft tissue of the 

 leaf, leaving the upper and lower surfaces uninjured, except that the 

 cells die and form large, irregular brown spots, having exactly the 

 appearance of vegetation scorched and shriveled by heat (PL XI). 

 In Porto Rico, and doubtless in other countries, these brown spots are 

 commonly interpreted as the results of exposure to the sun, and there 

 can be but little doubt that the ravages of this insect pest have had an 

 important influence in strengthening the opinions of those who advo- 

 cate heavy shading. Probably they are at least partially responsible 

 for many unwarranted statements hy writers making pretensions to 

 scientific accuracy, to the general effect that coffee "can not endure 

 the intense direct radiation of the tropical sun." The insect is very 

 small and would never be seen unless carefully searched for, while the 

 scorched spot is, to the general public, indisputable evidence that the 

 coffee has been injured by the sunlight. 



The ravages of the coffee leaf-miner have been investigated in 

 Brazil 1 and elsewhere, and the opinion is held that the damage is great- 

 est at low elevations and in trees exposed to the sun. 2 In Porto Rico 

 the latter idea seemed to apply well to the recently exposed trees, but 

 those which had never been shaded were often quite free from injury, 

 and were nowhere noticed to be seriousty affected. It is true that 

 trees in very heavy shade do not suffer from the leaf-miner, but in 

 regions where the insect is abundant the shaded trees are not entirely 

 immune, although the burrows seem to remain smaller than in debili- 



1 Mann's report of his investigations of the coffee moth (American Naturalist, 1872, 

 6: 332-341; 596-607) in Brazil is almost exclusively entomological, and, beyond the 

 statement that the larvae are said to attack the new leaves in early spring, nothing is 

 recorded regarding predisposing causes. It was estimated that the injury amounted 

 to about one-fifth of the coffee crop of Brazil, but no remedy was found other than 

 that of picking off and burning the affected leaves before the escape of the larvae, and 

 although this process would be expensive, it was estimated that the gain in yield 

 would more than compensate. The insect probably came originally from the East 

 Indies, but was introduced into Brazil from the Antilles. Every precaution should 

 be taken to keep it from any coffee regions where it has not yet appeared. 



2 The depredations of this insect are now known to be avoidable by planting Libe- 

 rian coffee, which is much more hardy than the Arabian at low elevations, and also 

 much more resistant to fungous and insect diseases. 



