CHAPTER VI 



DISEASE AND INSECTS 



IT may be said fortunately that Irises are usually free 

 from both animal and vegetable attack. Insects are 

 very rarely found, and ordinary kinds, if met with, could 

 easily be dealt with by usual methods. There is, how- 

 ever, an "Iris Fly," which affects /. orientalls (better 

 known as /. ochrokuca) and its allies, and, from the 

 account given, the only way of dealing with it would be 

 to destroy the leaves, though experience alone could 

 determine whether this is necessary. It was described 

 by the late Mr I. O. Westwood in the Gardeners' 

 Chronicle of April 2 1st, 1 888, p. 493, and a good figure 

 accompanies the article. The insect was apparently new, 

 for the generic name Agromyza is suggested provision- 

 ally, with the specific name Iridis. Comparison is made 

 with the leaf-miner of the Marguerite, and in this 

 case also the damage is done by the larvae which feed 

 upon the soft internal tissue of the leaf, causing patches 

 of lighter colour on both sides. It is satisfactory to 

 know that in spite of position within the leaf, the larvae 

 are attacked by a parasite, a beautiful little Pteromalid 

 of golden green colour, with yellow legs. The larva 

 of the Agromyza, upon which it preys, is about f$ of 

 an inch long, and the fly is black, about an eighth of an 

 inch long, with a wing expansion of a quarter of an 

 inch. The wings are hyaline, finely veined with black, 

 of yellowish tinge towards their base. It may be 

 possible to destroy the larvae by squeezing them with 

 finger and thumb while in the leaf. 



