F. II. Petherbridge and M. A. Husain 201 



is easily seen by the naked eye through the chitin. Lips of this gland very 

 light brown and not so noticeable as in P. rugicollis. 



Yellowish green in colour, eyes dark red with a white margin round 

 them. Thorax and abdomen covered with long white hairs. Antennae 

 light orange with a dusky chitin ; terminal joint of same colour, not pink 

 as in P. rugicollis. Other characters typical of first Instars (see p. 199). 



Instar II. Length 1-6-1 -8 mm. 



Peculiarities typical of Listar II (see p. 199), otherwise as Instar I 

 except for a slight bluish tinge, especially underneath. 



Instar III. Length 1 •9-2-4 mm. 



Peculiarities typical of Instar III (see p. 199), otherwise as previous 

 instar. 



Instar IV. Length 2-7-3-5 mm. 



Peculiarities typical of Instar IV (see p. 199), otherwise as previous 

 instar. 



Instar V. Length 3-9 mm. 



Peculiarities of Listar V (see p. 199), otherwise as previous instar. 



The last three instars have a definite bluish tinge. 



7. PSALLUS AMBIGUU8 (FALL.) (OBSCURUS D. AND S.). 



This species hatches out about the same time as P. rugicollis. 

 A large number were found in the orchards at West Walton. They are 

 very shy during the first two stages and lie concealed in the axils of 

 the leaves and it is very difficult to see them and still more difficult 

 to dislodge them by beating or shaking. They were found equally 

 frequently in damaged and undamaged buds, and their behaviour in 

 cages and in sleeves definitely proved that these were not associated with 

 the injury done to the leaves and fruit. They were present at the Uni- 

 versity Farm, Cambridge, and at Histon where there was no trace of 

 damage. We found them too frequently on apple shoots brought for 

 our cages, but never found any damage on these and consequently we 

 regard this species as harmless. One fact is very significant and requires 

 elucidation. As pointed out above the larvae of Psallus amhiguus lived 

 for weeks on absolutely dried shoots with no leaves and several of them 

 reached the fourth instar stage. This suggests that their source of food 

 may be something other than plant juices. There were present on these 

 twigs, eggs and nymphs of the apple sucker {Psylla mali) and also eggs 

 and young of the red spider {Tefrani/chus sp.). There is no doubt that 

 they do suck plant juices as we have seen them doing so, but we have also 



Ann. Biol, iv 14 



