20 -AUSTEALIAN SUGAE-CANE BEETLES AND THEIR ALLIES. 



These twelve egg-chambers had an average depth of 12^ inches, and 

 averaged 28-2 eggs each. Hence, ^dth the numerous young grubs that 

 we found near the surface, these four stools would average well over 100 

 grubs per stool. The year before, the cane in this field was badly injured 

 by grubs, and I found as high as 134 grubs per stool. 



As mentioned above, it has been observed that these beetles in 

 confinement do not always place their eggs in chambers. Our observa- 

 tions on this point, however, indicate that such finds are chiefly due to 

 the soil being unfavourable for the beetles to construct a proper cell, 

 usually because it is too dry. If there is not sufficient moisture for the 

 particles to pack as the beetle compresses the walls of the chamber, they 

 fall in upon the eggs, and as she moves about in laying they become 

 scattered, giving the appearance that they were so placed intentionally. 



Furthermore, it has been repeatedly oljserved that the eggs will not 

 withstand dryness, for whenever they are exposed to the air, for even a 

 brief period, they burst open on one side and a part of the contents is 

 forced out. Hence instinct apparently teaches the beetle that her eggs 

 must be placed deep enough in the soil so that there will be no possiblity 

 of their becoming dry before hatching; otherwise she would not go to 

 all the trouble of placing her egg-chamber at such depths. 



Particular attention to this phase of the problem was called by 

 Girault and Dodd (66), who found by experiment that the eggs soon 

 shrivelled and dried up when placed in either dry soil or simply exposed 

 to the air. The eggs exposed in the sunlight naturally shrivelled more 

 quickly than those in the shade ; and they found, too, that even when the 

 eggs were covered with a shallow layer of moist soil they failed to hatch, 

 because the soil dried out too quickly and they became shrivelled. 



Effect of Desiccation on Ovipositing. 



To note the instincts of the beetles in this matter, an experiment 

 was started by the writer on 5th January, 1921, using four small cages, 

 with dust-dry soil from Greenhills. These were marked A, B, C, D, and 

 a gravid female beetle was placed in each. The soil in A was then 

 watered, so that it was very similar to that of the field, since this cage 

 was to be used as a check. 



On 6th January, A had laid in a chamber 1 inch by 1^ inches, at the 

 bottom of the pot 5 inches deep ; the 28 eggs appeared to be normal. 

 C had also laid ; 36 very small, white-looking eggs were loose in the dry 

 dust, near the centre of the pot, and the beetle was still buried ; dissection 

 showed that she still had several small undeveloped eggs in the ovaries. 

 B and D had no eggs, and both beetles were on the surface of the dry 

 soil. 



On 7th January, B was buried in the dust but had not laid. D was 

 on the surface in the act of laying, so I watched her for some time ; after 

 laying an egg she turned to the right a couple of times before settling 

 down to deposit another. This was preceded by a movement of the 

 pygidium and a forcing out of the vagina for about ^-inch, so that the 

 cement glands, which are dark in colour, could be seen on the outside. 

 The whole process required about five minutes for each egg. She 

 invariably turned round and round to the right, before laying the next 

 egg. The eggs were very sticky when first extruded, so that they clung 

 to particles of soil as well as to each other, wherever they happened to 



