14 



BULLETIN 616, U. S. DEPARTMENT OF AGRICULTURE. 



and from the latter part of September to November it will range 

 from about 12 to 14 days. 



Table IV. — Seasonal variations in duration of the larval stage of the citrus 

 thrips, Lindsay, Gal.; 1911. 



Period of season. 



Prevailing 

 mean 



tempera- 

 tures. 



Mar. 25 to Apr. 15 

 May 13 to June 3 . 

 June 13 to Sept. 5. 

 Sept. 4 to Sept. 21 

 Sept. 23 to Nov. 5 



° F. 



59.62 



62.58 



74.61 



67.47 



58.48 



All four molts of the citrus thrips, comprising two in the larval 

 stage and two in the pupal stage, are accomplished in about the same 

 manner. The first molt takes place on the leaves and fruit of the 

 host plant, the remainder in some secure hiding place, usually on the 

 ground. When ready to molt the larva ceases to feed and becomes 

 inactive. Tremors vibrate the antennas and body at brief intervals 

 for a period of from one to three hours, and the abdomen slowly con- 

 tracts and shrinks away from the old skin. Then follows an active 

 period of from 15 minutes to an hour, in which the middle and hind 

 legs are repeatedly stretched as far back as possible and slowly 

 drawn forward, while the insect goes through jerky lateral motions 

 with the body. The skin then splits from the vertex along the 

 dorsum to the abdomen, after which the insect becomes very active, 

 doubling down with the head between the fore feet and slowly re- 

 moving the skin from the head and antennas. The legs are then 

 worked out of their casings and the exuvium pushed back under the 

 body. The skin usually is attached at the tip of the abdomen to the 

 surface on which molting occurs, greatly aiding the insect in ex- 

 tricating itself. The skin generally is removed entire, but occa- 

 sionally antennal and leg casings are removed separately. Cool 

 weather greatly retards the process, which is more likely to be ob- 

 served when such weather prevails. Groups of larval skins re- 

 sembling specks of gray dust sometimes are found on orange leaves. 

 The molting process in the citrus thrips is similar to that observed 

 in certain Orthoptera. 



THE PUPA. 



DESCRIPTION. 



The propupa. — The propupa, or first instar (fig. 6), is very similar 

 in general appearance to the larva. It is generally somewhat paler 



