84 



[April. 



ON AN INTERMEDIATE " AONIDIFORM " STAGE IN ASPIDIOTUS. 

 BY E. ERNEST GBEEN, E.E.S. 



With reference to Mr. W. M. Maskell's interesting note {ante,\ 

 p. 33) on the possible identity of Aspidiotus per^iiciosus, Comstoek, 

 and Aonidia fusca, Maskell, I may mention that I have observed in 

 some species of Aspidiotus, at the time of the second moult, what I 

 might call an " Aonidiform stage." The insect shrinks away from its 

 pellicle prior to subsequent growth and rupture of its former skin. 

 A specimen examined only in this intermediate stage would be un- 

 hesitatingly placed in the genus Aonidia ; the supposed adult insect 

 being considerably smaller than, and contained within, the second 

 pellicle. I have, mounted in Canada balsam, a specimen of Asp. 

 secretus (Ckll. MSS.) in this stage, from which the annexed figure was 

 taken. The pellicle of the second stage is seen to be intact, and com- 

 pletely encloses the early adult insect, which subsequently increases 

 to many times its former dimensions. 



Possibly this fact may explain the similarity of anatomical detail, 

 with difference of formation of pu- 

 parium in the two insects mentioned 

 by Mr. Maskell. In which case 

 Aonidia fusca, Maskell, may be 

 considered an immature form of 

 Aspidiotus perniciosus, Comstoek. 



This theory might be corro- 

 borated or disproved by a close study 

 of the life-history of Asp. perni- 

 ciosus, which could best be effected 

 in its native or adopted country. 

 Perhaps Prof. Comstoek or Prof. 

 Cockerell may be in a position to 

 settle the question. 



The fact of this " Aonidiform " stage existing in some (if not all) 

 of the species of Aspidiotus suggests that the genus Aonidia is the 

 more primitive form. 



The displacement of the mouth parts in the pellicles of the 

 DinspidcB is remarkable, especially in Aonidia and Fiorinia, where the 

 ventral part of the skin remains unbroken. In the annexed fij'ure 

 the rostral apparatus of the discarded pellicle is seen near the pos- 

 terior extremity (at a). The distension of the skin of the anterior 

 part must be enormous. 



Bearsted, Kent : • 



Februartj lOlh, 1896. 



St.<S id 



