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THE PTINID BEETLE, TRIGONOGENIUS GLOBULUM. SOLIER, 

 BREEDING IN ARGOL. 



By Hugh Scott, M.A., Sc.D., F.E.S., 



Curator in Entomology, University of Canihridi!,c. 



In March 1920 my attention was called by Dr. F. W. Dootson, Uni\'crsity 

 Lecturer in Chemistry, to the fact that a beetle was breeding in numbers in a jar 

 of argol in the Chemical Laboratory of Cambridge University. The insect proved 

 on examination to be the introduced Ptinid, Trigonogenius globulum, Solier,* a 

 form related to the household insect, Niptiis hololcucns, to which it bears at first 

 sight a slight resemblance. 



Argol is the crust or deposit which separates out in barrels of new wine. It 

 contains a high percentage of cream of tartar (potassium bitartrate), and most of 

 the pure stock of that chemical is prepared from it. The argol in which the beetles 

 were living was found to contain about SO per cent, of potassium bitartrate. The 

 argol was a purplish-red powder of close consistency, and it came to the Chemical 

 Laboratory from London in a bag in 1913. It was placed in an earthenware jar, 

 tightly corked with a wide cork bung. The powder did not quite fill the jar, but a 

 very small air-space was left at the top.j I am assured that the jar was not opened 

 from the time the powder was put in till early in 1920, when the argol was found to 

 be full of adults and larvae of the Trigonogenius. The cork, which I have twice 

 examined, has not been bored through or damaged by insects in any way, and it 

 fits so closely that it is almost impossible that the beetles can have got into the jar 

 down the side of the cork ; nor have they been noticed anywhere else in the 

 laboratory. Probably, therefore, some of the insects were in the argol when it came 

 to the laboratory and have continued breeding in it all these years. No other kinds 

 of insects were found in the argol. I am indebted to Dr. Dootson for most of the 

 foregoing particulars and for samples of the infested chemical. 



That the beetles were nourishing themselves, not exclusively on the 80 per cent, 

 of potassium bitartrate, but at any rate partly on some of the ingredients forming 

 the other 20 per cent, of the argol, seems to be indicated by the following experiment, 

 carried out at Dr. Dootson's suggestion. Some of the insects were placed on the 

 surface of about two inches depth of pure cream of tartar in a wide-mouthed corked 

 bottle, with plenty of air-space between the surface of the chemical and the cork ; 

 32 adults and 15 larvae were placed in this on 12th March 1920. Three and a half 

 hours later almost all the larvae had burrowed down into the white powder, but the 

 adults were still on the surface and showing signs of discomfort. Next day all the 

 larvae but one were below the surface, and also about 23 of the adults ; the remaining 

 adults were still on the surface and one was dead. No further observation was 

 made for nearly three weeks, when (on 1st April 1920) about 14 adults and one larva 

 were seen to be on the surface, while the other 18 adults and 14 larvae had all burrowed 

 some way down into the cream of tartar, and several burrows were visible against 

 the glass sides of the bottle. The bottle was not examined again for nearly a year, 

 when (on 15th March 1921) its contents were turned out, and all the insects were 



* Described by Solier in C. Gay's " Historia de Chile," iv, 1849, p. 464. I have retained Solier's 

 original spelling of the specific name, though in some later works globulitin is altered to globulus, 

 which is probably more correct. Solier called the species globulum, but at the same time named 

 a variety of it globosus. Why he gave the former name the neuter ending is difficult to say. 

 He may have intended globulum to be a noun, but in several dictionaries of classical and late Latin 

 which I have seen, the only form of the word is a late Latin noun, globulus. 



t In some of the argol which was put into a glass-stoppered bottle, filling it up to the stopper 

 and leaving no air-space, all the insects died. 



