18 BULLETIN 616, U. S. DEPARTMENT OF AGRICULTURE. 



The rostrum, or mouth-cone, is short and blunt, not quite reaching 

 across the prothorax, and is tipped with black. The prothorax is 

 slightly wider than the head, slightly narrower than the mesothorax. 

 The female is broadest through the middle segments of the abdomen, 

 tapering gradually both ways ; tip of the abdomen conical, fitted with 

 a sawlike ovipositor. The abdomen of the male tapers gradually 

 from the second segment to the tip, which is bluntly rounded ; a pair 

 of reddish brown testes is visible through the body wall at the sixth 

 and seventh segments. More or less conspicuous spines occur on the 

 wings and near the hind angles and at the tip of the abdomen. 

 Under high magnification the abdomen is seen to be regularly beset 

 with minute hairlike processes. 



DURATION OF ADULT LIFE. 



Owing to their extreme activity, minuteness, and delicacy, many 

 of the adult thrips under observation were killed accidentally and 

 others probably injured in changing their food. For this reason 

 only the data upon specimens which lived 20 days or longer are con- 

 sidered in discussing the length of adult life. In only a small per- 

 centage of the cases considered did the length of life run as low as 

 20 days. The maximum duration was 49 days, which is also prob- 

 ably exceptional. The variation of 29 days occurring between the 

 accepted minimum of 20 and the maximum of 49 days is probably 

 as great as ever occurs in the field among specimens not affected by 

 accident, disease, or enemies. In nearly 70 per cent of the cases con- 

 sidered the insects lived 25 days or more, and in 85 per cent they 

 lived 35 days or less. The average age attained by the shortest-lived 

 specimens may therefore be set safely at 25 days, and that of the 

 longest lived at 35 days, the mean between the two being 30, which 

 corresponds closely with the general average from all which lived 

 over 20 days. The insects lived only from 3 to 6 days without food. 



INFLUENCE OF THE WEATHEB ON GROWTH AND BEHAVIOR. 



The citrus thrips is purely a product of the arid Southwest and 

 flourishes only in a hot sunny climate. The fact that it does not 

 thrive in coastal sections nor in any part of the humid belt of the 

 Lower Austral life zone shows its sensitiveness to conditions of tem- 

 perature and moisture. The insect flourishes best on sunny hill 

 slopes. It appears to enjoy the direct rays of the sun, and by pref- 

 erence seeks the more exposed leaves and fruits in the upper and 

 southerly expansion of the trees. On bright warm days of summer 

 the adults exhibit marked restlessness and increased reproductive 

 activity. The duration of the immature stages is shortened, molting 

 is accelerated, and the rate of emergence is increased greatly. The 



