ON THE LAND

Nelson Evening Mail, Volume LXXII, 30 January 1939, Page 4

ON THE LAND

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RAPE CROP PESTS

DIAMOND-BACK MOTH DETAILS OF EXPERIMENT PROGRESSING IN HAWIvES BAY VISIT OF MR J. MUGGERIDGE Details of an experiment for the control of the diamond-back moth, now in progress in Hawkes Bay, were given recently by Mr J. Muggeridge. Government entomologist in the Division of Entomology stationed at the Cawthron Institute, Nelson, who was on a visit to Howkes Bay. Mr Muggeridge was formerly stationed at Palmerston North and was raesponsible for the introduction of the parasite which has effected the control of the white butterfly in New Zealand, says the "Napier Telegraph.”

The experiment now being carried out follows the introduction to New Zealand of new parasites from the Homeland, one or both of which it is hoped will assist in gaining control over the diamond-back moth, and is being investigated by the Division of Entomology of the Department of Scientific and Industrial Research at the Cawthron Institute in conjunction with officers of the Department of Agriculture. Mr Muggeridge pointed out that the present work was purely experimental and the results indefinite.

In carrying out the experiment the Department of Agriculture has obtained the co-operation of Mr W. McKenzie, Havelock North, where the trial is situated. Mr Douglas Tod. of the Cawthron Institute, has been placed in charge of the actual work and is engaged in arranging cages containing the diamond-back moth on rape crops in the property. Into these cages the new parasite is released, and during the next lew weeks the operations of this parasite will be closely watched. If successful, it is hoped to establish the parasite throughout the district. At the present time, however, no supplies of the parasite arc available for use outside the experiment at Havelock North. COMPARISON WITH NELSON In the meantime a further experiment is being carried out in the Nelson district, where a different type of parasite is being released in the same manner. Whereas the parasite in the Hawkes Bay experiment is what is known as a pupal parasite, howevet, operating much in the same way as the parasite which has controlled the white butterfly, the insect which is engaged in the Nelson experiment is known as a larval parasite. The names of the two parasites are Diadromus and Angitiacerpophaga respectively.

SELECTION OF AREAS Mr Muggeridge stated that the Hastings district had been selected for the experiment in view of the fact that there were many small areas of crops attacked by the diamond-back moth in the district, and in the event of the trial proving successful it would be comparatively simple to establish the parasite under the conditions ruling. "I would like it to be understood that the work is purely experimental, and one cannot even guess as to whether the parasite will prove successful or not,” said Mr Muggeridge. In regard to the control effected by the parasite over the white butterfly Mr Muggeridge remarked that the greatest problem with which they were faced at the moment was to find some way of stopping the butterfly from gaining the upper hand during certain conditions.

The control effected by the parasite up to the present time this season was certainly most satisfactory, and this control might be continued right through the season. There was nothing to guarantee this position, however, for weather conditions which were favourable to the butterfly and unfavourable to the parasite might easily bring about an infestation of the butterfly later in the year. If might then be some time before the parasite again assumed control.

It was this variation in the efficiency of control that was engaging attention at the present time, and it was hoped that some success would be achieved ty the introduction of further parasites to assist the present one in its operations

Trials with such parasites were now being carried out, said Mr Muggeridge, and it was hoped that they would prove successful and the white butterfly menace be brought even more strictly under control than at the present time.