THRIPS. 195 



•egg will bear freezing, but that at a uniform tempera- 

 ture of 85°, the time required for hatching was 31 

 days ; at a temperature of 50°, the time needed was 

 11(5 days. Other dates are given, showing that so long 

 as the warmth was considerable, — that is, not lower 

 than 60°, — though the time of hatching was lengthened 

 increasingly with the drop in temperature, yet it was 

 not very greatly altered ; but below 60" the time was 

 much lengthened. . 



How far these experiments may apply to eggs of 

 our farm-pests we cannot be quite sure till we have 

 proved it, in each case ; but if, as is likely, the eggs 

 will hatch at a moderate depth below the surface, and 

 the grubs perish because they cannot come up, we 

 -have a useful piece of information ; and further, in 

 ■the fact of eggs lying unhatched and also uninjured 

 ■when buried deeply, we may have a reason for the 

 •occasional entirely unexpected appearance of some 

 crop-pest in a single field, but nowhere else in the 

 neighbourhood. 



But however this may be, we have instances here 

 of the use of putting eggs in unnatural places and 

 circumstances, and for this purpose no means are 

 (better than thorough cultivation of the land. Thus 

 "whilst — just as with weeds— a number of the eggs are 

 turned safely down to a depth from which we may 

 hope they will not come up again, others will escape, 

 but there will be a certain quantit}^ destroyed by wiiat 

 is termed desiccation, or drying. If an egg which is 

 naturally placed below the surface of the earth, is 

 thrown out on the surface, to the effects of air and 

 sunshine, the fluid within will dry up, and the embryo 

 wdtliin will consequently be destroyed. 



The remaining order is that of the Tlirips, Tliy- 

 sanoptcra. These are very small insects, which some- 

 times do much harm to corn. They are nearly alike 

 in shape in all their stages, but as they are scarcely 

 large enough to be seen by tbe naked eye, the figure 

 gives a better idea than description (see Fig. 151). 



