138 



do so by penetrating the husks the relation can hardly be a direct one 

 of cause and effect. The presence of husk leaves is also shown to be 

 undesirable. By recording the number of larvae in each ear it is 

 possible to resolve the total damage into the number of larvae and the 

 average amount of injury done by each. In the more immune varieties 

 both the number of larvae and the damage per larva were low. Since 

 the number of larvae must be determined largely by the choice 

 exercised by the moth in depositing eggs, it follows that the plants 

 avoided by the moths are also those that the larvae find most 

 distasteful. This identity of instincts in adult and larva is difficult to 

 exj)lain as the result of morphological characters of the plant and 

 seems to indicate that at least a part of the immunity is the result of 

 chemical differences, perhaps the presence of some volatile substance 

 distasteful alike to both stages. Both in California and Maryland the 

 injury from H. obsoleta decreased slightly as the season advanced. 



These experiments indicate that by increasing the length and 

 thickness of the husk-covering and reducing the husk-leaves, varieties 

 of sweet maize can be produced in which damage from H. obsoleta is 

 materially lessened. No difficulty was experienced in securing by 

 hybridisation and selection the desired plant characters in combination 

 with the seed characters of sweet maize. 



Illingworth (J. F.). The Sugar-Cane Grub Pest. — Queensland Agric. 

 Jl., Brisbane, viii, no. 3, September 1917, pp. 173-175. [Received 

 24th January 1918.] 



In these notes the author lays particular emphasis upon the benefit to 

 be derived from cultural operations in sugar-cane growing. The problem 

 of the control of sugar-cane grubs is not an easy one. The introduction 

 of parasites into Queensland would probably be of little avail, since 

 the cane grubs are native insects, and introduced parasites have only 

 been successfully used against introduced pests. There are already a 

 number of parasitic and predaceous insects attacking the grubs, but 

 these are themselves largely attacked by other parasites. About one- 

 third of the grubs appear to succumb to the attacks of bacteria and 

 parasitic fungi, and these undoubtedly lend themselves to artificial 

 propagation and transplanting. The soils of badly-infested fields 

 were all found to be very poor in humus and usually contained no lime 

 and these two factors appear to be of vital importance to the growth of 

 sugar-cane in a grub-infested district. The chief food of the grubs is 

 decomposing organic matter in the soil and, if this is lacking, they are 

 forced to feed upon the Hving roots of plants. Lime improves the 

 character of the soil by hastening the humification of plant tissues and 

 its action is also favourable to the development of fungous parasites. 



The general custom in all grub-infested districts has apparently been 

 to destroy the principal humus-forming elements by burning all the 

 rubbish and failing to grow sugar-cane in rotation with a green crop. 

 The conservation of soil moisture is an important factor in the growth 

 of cane, making it more resistant to the attacks of grubs, and also 

 materially assisting the development of fungous organisms destructive 

 to the grubs. These cannot thrive in dry soil ; hence the well-known 

 fact that grubs are more destructive in a dry season or upon dry soil. 



