OBSERVATIONS ON COTTON THRIPS, 97 



Sometimes it moves only two or three centimetres, but at other times greater 

 distances, before commencing to feed. As it imbibes the sap of the plant, the body 

 takes on a yellowish hue, and usually by the second day the reddish bands, so very 

 characteristic of all stages except the adult, begin to develop. Only one moult has 

 been observed — the change from the larva to the prepupa in the soil. 



Like the adult, the larva feeds by piercing and sucking the juices of the plant. It 

 prefers the lower surface of the leaf, though it does not by any means confine itself 

 there. Movement from one surface of the leaf to the other is common, but from one 

 leaf to another is exceptional. Larvae are often found segregated along the veins of 

 the leaf, and occasionally in colonies on other parts of the leaf. 



Like many species of thrips, the larva carries a globule of brownish black excreta 

 (on the first day the excreta are colourless), which, after attaining a considerable size 

 and dropping on the leaf, dries to a blackish spot. These spots discolour the leaf, and 

 their presence is a sure indication that the plant has been, or is being, attacked by 

 the thrips. This globule of excreta is held off the surface of the leaf owing to the 

 anal segments of the larva being shghtly turned upwards. 



The larvae when full grown drop from the leaf, and, crawling into a convenient 

 crack in the soil, there change to prepupae. They prefer damp earth, and the 

 prepupae are usually found at the junction of the damp and dry soil, which varies 

 from about three to six inches down. Immature larvae falhng to the ground will die 

 if they cannot find food in the nature of weeds or crawl back to the plant, a very 

 doubtful possibihty. It may be noted that practically all weeds growing amongst 

 the cotton support larvae. If the land is kept clean [whilst the cotton crop is 

 growing, this will not only prevent the larvae from maturing, but will make the 

 adults seek other plants for oviposition. According to experiments, the adults do 

 not Hve more than a day without food. 



The larvae usually like to secrete themselves away from the sun, and are often 

 found in large numbers in the curled up parts of the leaf. Larvae in the soil do not 

 feed, and, if disturbed, move more quickly than on the leaf. 



Habits of the Prepupa and Pupa. 



The prepupae and pupae are found in the soil, though under unnatural conditions 

 they have been observed on four occasions on the leaves. This pecuharity was not 

 seen in the field. The larva, before prepupating, does not appear to make any cell, 

 but crawls into any convenient place in the soil. The cast skins of the larvae and 

 prepupae are found together, indicating that no movement of prepupae and pupae 

 takes place. Both stages are capable of movement when disturbed, and are often 

 seen in groups, and at other times singly or in pairs. The want of moisture in the 

 soil does not have any deleterious effect, but from experiments and observations 

 it would appear that if, after the larvae have crawled into the soil, the soil is kept 

 moist and not allowed to crack, the adult is unable to emerge. 



The prepupae and pupae possess red bands like those of the larvae ; but whilst in 

 the prepupae the antennae are carried forward in front of the head and the wing-lobes 

 are partially formed, the antennae of the pupae are bent backwards over the head 

 and the wing-lobes are well developed. The darkening of the body of the pupae 

 previous to the emergence of the adults is very evident. 

 (687) . a2 



