April, '13] JONES: FALL ARMY WORM 233 



some extent. The few larvae collected on January 23 were those of 

 Remigia repanda and an unidentified species, though, from the de- 

 scription of the "worms" that had been so common, it seems prob- 

 able that larvae of Laphygma frugiperda had, with those of Remigia 

 repanda, done practically all the damage. 



The "southern grass w^orm" is sometimes found on young plant 

 sugar cane, working on the opening whorl of leaves. This injury may, 

 apparentl}^, occur on cane planted at any season of the year. 



Injury to young seedling canes has been observed at Rio Piedras, 

 the larvae possibly having originated in the grass used for shade on the 

 boxes in which the seedlings were growing. 



Corn growing in Porto Rico is severelj^ attacked by a number of 

 insects and Laphygma frugiperda is an important pest of this crop. 

 The injury is largely' confined to the inner leaves of the young corn 

 plants, though when the plants are very young the larvae, of necessity, 

 sometimes work on the outer leaves. 



Possible Factors Governing Abundance. Outbreaks of the 

 "southern grass worm" in Porto Rico occur only at certain periods. 

 These outbreaks appear to be governed by climatic conditions; occur- 

 ring during the fall and winter seasons when there is an abundance of 

 rainfall and when the temperature is somewhat lower than at other 

 seasons. There is, during these seasons, a more abundant growth of 

 grass, wdiich may be favorable for the development of the larvae because 

 of the abundance of food. 



Abundance of larvae following floods may perhaps be due to the 

 fact that when the rivers recede there is left on the areas, previously 

 covered by the water, more or less additional vegetable debris and 

 soil. This deposited material ma}^ contain eggs or larvae which the 

 surface water from the watersheds of the rivers has brought down and 

 which would, therefore, be concentrated on the overflowed areas when 

 the rivers subsided. 



It may be that unsuitable conditions, such as abundance of water, 

 lack of food, or lo"wer temperature, in certain sections, cause the species 

 to seek other areas. If there is a migration, it would be interesting 

 to decide what factor or factors are accountable for the selection of 

 any particular area in which to breed. 



In all of Mr. Van Dine's field notes on this species it is stated that 

 the injury to sugar cane was in fields of young plant cane. This 

 appears to be the case both when the larvae occur in great numbers 

 and when they are present in small numbers, scattered through the 

 fields. This may be due to the fact that, in. the vegetation growing 

 on the land, previous to the planting of the cane, were natural food 

 plants of Laphygma frugiperda, the species attacking the cane after 



