SPECIES ATTACKING JOINTS INTERNALLY. 25 



In hothouses the use of a solution of whale-oil soap or of tobacco 

 stems is recommended for this and other scale insects of cacti. Any 

 preparation that may be used should be applied with considerable 

 force by means of a spray pump in order to reach the insects in the 

 crevices of the plants. 



Minor Species Attacking the Joints Externally. 



In addition to the species described in the preceding pages a con- 

 siderable number of forms have been found which occasionally feed 

 upon the joints. None of the other forms is at present known to be 

 of any great economic importance, although they are likely to become 

 abundant and injure the plants under local conditions at any time. 

 The species more likely to do so are mentioned in the following 

 paragraph. 



Diaspis echinocacti cacti Comstock is a grayish scale insect, the 

 females circular and the males oblong. It sometimes becomes so 

 numerous as to cover entirely the surface of the joint. This con- 

 dition is shown in an accompanying illustration. (PL V, lower 

 figure.) In artificial plantings and in hothouses this species is of 

 some importance. Under field conditions it rarely reaches excessive 

 numbers. Dactylojnus tomentosus Lamarck, which resembles the 

 cottony cochineal insect but differs from that species by the fact that 

 the separate individuals, instead of masses of several individuals, are 

 covered by the cottony secretion, may be destroyed by the means 

 recommended for the cottony cochineal insect. The white ant Tennes 

 flavipes Kollar feeds upon a great variety of cactus plants and has 

 been observed to injure the joints thrown on the ground for growing 

 a new crop. It sometimes constructs nests in the damaged joints. 

 The scale insect Eriococcus coccineus Cockerell has been recorded 

 from California. Aphis medicaginis Koch, a plant louse, apparently 

 passes the winter on Opuntia in Texas. During the remainder of 

 the year it is seldom found on Opuntia plants, and on the whole 

 causes only very slight injury. 



SPECIES ATTACKING THE JOINTS INTERNALLY. 



Melitara junctolineella Hulst. 1 



Melitara junctolineella Hulst and the other species of the genus 

 are true cactus insects. They may be recognized from the following 

 brief description: Large indigo-blue (young) or conspicuously 

 banded (last stage) larvae living within the joints of Opuntia, cause 

 large excavations and tumor-like swellings of the infested joints. 

 The adult is a grayish moth of an expanse of 1^ inches. 



The eggs of this species are very similar to those of Melitara pro- 

 denialis Walk, which are described on another page. They are 

 deposited in exactly the same manner. The remarkable arrangement 



1 Order Lepidoptera, family Pyralidae. 



