63 



THE LIFE-HISTORY OF EUTHYRRHINUS MEDITABUNDUS. FABR., AN 

 IMPORTANT WEEVIL PEST OF MANGO TREES IN AUSTRALIA. 



By G. F. Hill, F.E.S. 

 (Plate III.) 



The adults of the weevil, EuthyryJiiniis meditahundiis, Fabr., were frequently 

 taken in the forest country to the south of Darwin, Northern Territory, and on several 

 occasions they were bred from the branches of two species of indigenous trees and from 

 custard apples, Poincianas and two unidentified species of introduced ornamental 

 trees growing in the Darwin Botanic Gardens. As a rule the infestation of these 

 trees was not heavy, although Poincianas occasionally showed considerable injury. 

 Mango trees, which were frequently badly damaged "and sometimes destroyed by 

 termites {Mastotermes darwinensis), appeared to be immune from attack by 

 Euthyrrhinus, even when growing in close proximity to infested trees of other kinds." 



Later, while a resident of Townsville, North Queensland, I had opportunities of 

 studying the habits of this insect in the role of a mango pest of the first importance. 

 Although these trees are not grown extensively for commercial purposes, they are 

 to be found in many North Queensland gardens, where they are prized not only for 

 their shade and beauty, but also for their prolific crops of fruit. 



The following notes are the result of observations made on a number of large 

 mango trees growing in the vicinity of the Australian Institute of Tropical Medicine, 

 Townsville. In March 1919, two trees in particular attracted attention owing to the 

 number of dead twigs appearing through the dense foliage at the summit, and although 

 a close examination was not made then, the condition was attributed to the effects 

 of drought during the preceding dry season. During the dry season of 1919 (April to 

 the end of December) the condition of these trees gradually became worse, and others 

 in the vicinity showed symptoms of disease. Early in "this year (1920) one tree 

 threw out bunches of leafy shoots along the main and upper branches, but the older 

 foliage continued to fall. At the end of April this tree died, and of the other there 

 remained alive only one secondary branch and a strip of bark extending from it to the 

 ground. From that month (April) to the end of August the beetles emerged in great 

 numbers from the trunks and main branches. Those beetles which emerged from the 

 now dead tree migrated at once, presumably to living trees in the vicinity, while those 

 from the other gathered on, and oviposited" in, the remaining living portion. 



Upon emerging from their holes the beetles are very active and begin at once to 

 seek mates. The act of copulation occupies about ten minutes, after which the male 

 remains attached to the female for some considerable time — two or three hours in 

 some cases. During copulation the females, and afterwards both sexes, gnaw away 

 the outer weathered surface of the bark and feed upon the living tissues or sap beneath, 

 leaving small areas of exposed tissue to mark the feeding places. This injury is 

 negHgible, even when many beetles are confined in close captivity to a small 

 area of bark. 



Oviposition. 



The average period of development of the embryo within the ovary has not yet 

 been satisfactorily determined. On 6th August a pair were observed "copulating" at 

 noon, and an hour later they were removed to a healthy mango tree, on which they were 

 enclosed in a small wire-gauze cage tacked to the bark. During the following three 



