Destruction of Mites by Heat. 
273 
upon minute fungoid growths parasitic on tree trunks. It has 
been referred to more than once in these Reports as particularly 
common on lime trees, and many people remain unconvinced 
of its innocence. 
With this exception, the animals found in the diseased 
shoots were beyond suspicion, being chiefly mites of carnivorous 
habits and the aphis-eating grubs of Syrphidse or “hover flies.” 
Theobald has described a somewhat similar appearance as 
being due to the grub of a sawfly of the genus Emphytus , but 
no such grubs were found in this case, nor was there any 
definite channel such as they would make, and the mystery 
remains for the present unexplained. It would be interesting 
to know whether other fruit growers have observed the same 
phenomenon, and if so, what varieties of apple tree are most 
affected. Perhaps next year an opportunity will arise of 
examining the first stages of the diseased growth. 
Fortunately no great injury seems to be done to the trees, 
the swelling being confined to the pruned stump and apparently 
not interfering with the new growths. 
Destruction of Mites by Heat. 
In July I was asked to make some experiments with the 
view of ascertaining the possibility of destroying mites 
infesting stored material by heat without damage to the 
material itself. The material in the particular case was 
tobacco in the form of cigars, and the agricultural importance 
of this was not at first obvious, but the principle seemed to 
have a wider application, and the experiments were accordingly 
made. 
It was necessary to employ a thermostat, an apparatus with 
a chamber which can be raised to any desired temperature and 
kept steadily at that temperature as long as the operator 
wishes, and Professor Nuttall kindly placed one at my disposal. 
The mite in question was Glyciphagus spinipes , one of the 
Tyroglyphidse, or cheese-mite tribe, a common species infesting 
all sorts of stored produce and frequently to be met with in 
grocers’ stores. When the boxes were opened the minute 
creatures were seen actively running about, but they were 
quickly out of sight, hidden among the cigars. These showed 
no sign of injury ; but of course the presence of the mites was 
objectionable and calculated to diminish the value of the 
article. Preliminary experiments were made by capturing 
many of the mites and placing them in glass tubes which were 
then exposed in the thermostat to various temperatures and for 
varying periods. They quickly succumbed to a very moderate 
heat ; indeed, the attempt to ascertain the lowest temperature 
fatal to them was soon abandoned, for it was realised that this 
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