503 



outbreak was not investigated till the end of September, when the 

 caterpillars were just beginning to pupate, so that it was too late to 

 attempt any remedial measures. 



The small numbers of the larvae observed, in view of the damage 

 done, was astonishing. This may be accounted for in two ways — 

 cannibaUsm, a common habit of such larvae when their food-plants 

 are lised up, and disease, which sometimes sweeps off cut-worms 

 wholesale, and of which many larvae in this instance had apparently 

 died. Birds probably had no effect on them, as the caterpillars are 

 nocturnal when healthy. 



Should sufficient of the present brood survive to render a second 

 generation of importance, the damage will probably be done in 

 November, when the wheat in the ear is well forward. 



Cockayne (A. H.). The New Zealand Grass-Grub. Some Notes on 

 its Control. — New Zealand Jl. Agric; Wellington, xxi, no. 1, 20tli 

 July 1920, pp. 1-5. 



The life-history of the grass-grub, Odontria zealandica, has not been 

 completely worked out, but enough is known to indicate the general 

 course of it. Most of the eggs are laid early in the summer (November). 

 The adult beetles have been found during most of the year, but except 

 for the great brood that emerges in November they are not of any 

 importance. The young grubs feed on the roots of plants, especially 

 fibrous roots such as those of grasses, though in the seedUng stage 

 any type of plant, including trees, is likely to be kiUed. They feed till 

 the following spring, though they are in a more or less quiescent state 

 in the winter, pupating in October. 



On practically no grass-land in New Zealand are they ever absent, 

 but their ravages are more or less periodic, which is due to two factors — 

 an increase in the number of grubs in any particular area, and ex- 

 tremely dry weather conditions causing lessened root-production. 

 When numerous, grass-grubs thoroughly pulverise and loosen the 

 ground below the first two inches or so from the surface, and lessen the 

 capillary rise of water. Thus in dry weather the grasses that have 

 been eaten through cannot form new roots quickly, as the surface 

 layer of the soil becomes too dry. 



In grass-lands the main damage is caused either in the grasses' 

 first year of development, mainly in the autumn following spring 

 sowing, or after some years, when the plants have passed their most 

 vigorous root-development stage. Grass sown with rape in October 

 and November generally escapes damage, probably because the ground 

 is bare at the time of egg-laying, and is therefore not selected by the 

 beetle for the purpose. The main reasons why grass sown with 

 cereals — especially spring-sown oats — is seriously damaged are the 

 readiness with which the beetles lay their eggs in cereal crops, and 

 the weak rooting and poor estabUshment of the grass. 



There is no practical method for the control of grass-grub on farm 

 land by trapping, poisoning, burning, or by chemical treatment, 

 though quite small areas may be treated by fumigation with carbon 

 bisulphide. Nothing of any practical nature can be done except 

 re-seeding or rotation cropping. Measures on these lines are discussed 



