100 DECIDUOUS FRUIT INSECTS AND INSECTICIDES. 



TOTAL DEVELOPMENTAL PERIOD. 



The total developmental period varies from 20 to 28 or 30 days in 

 the majority of individuals, although in those individuals of each 

 generation which hold over for a time after the normal time of emer- 

 gence it may be from twice to several times as long as this. This 

 portion of the life history was actually determined for only three 

 individuals. One of these required 22 days and the other two 23 

 days each. One other was carried through the total period with the 

 exception of the incubation period. Estimating this at 5 days the 

 total developmental period for this individual was 36 days. During 

 the time it was developing, April and May, the weather was very cold 

 and the larval period was 22 days in duration. 



EXTENT OF DAMAGE. 



So serious a menace is this insect to the peach and plum trees that, 

 in a favorable season, the trees are completely defoliated in August. 

 Morgan figures a plum orchard which was practically defoliated as 

 early as May 22, 1897, when the photograph (PL XI) was taken. 



In the struggle to repair the damage of the slugs, the trees keep 

 putting out new leaves and forming new wood, which causes them to 

 enter the winter unprepared and less able to withstand freezing. 

 Many of them are thus winter-killed. 



Morgan (loc. cit.) quotes a letter from a correspondent in central 

 Louisiana, in which the statement is made that the species " kills an 

 orchard effectually in about two years." 



He also makes the following observation: "The attack of this insect 

 upon the American type of plums, such as the Mariana, and the almost 

 entire immunity of the Japanese varieties is very noticeable. Peaches 

 seem worse affected upon the lighter soils of the State." 



A heavily infested tree has a very characteristic appearance in the 

 late season, being entirely bare of foliage except at the tips of the 

 twigs, where tufts of new leaves appear. 



NATURAL ENEMIES. 



Although the nauseous, slimy covering of the larva of this species 

 undoubtedly protects it from many insects and other animals which 

 might otherwise attack it, it is not entirely without natural enemies. 

 Morgan (loc. cit.) mentions two species of mud daubers, which were 

 observed constantly visiting the infested trees and carrying away 

 the larger larvas, and records the bordered soldier-bug (Stiretrus 

 pulcheUa [=anchorago Fab.]) as feeding on them. He also records 

 having observed a hymenopterous parasite, Trichogramma minutum, 

 ovipositing in the eggs of the sawfly. The adults of the parasite 

 appeared in 8 days (May 22 to May 30, 1896). 



