The study involved determination of resistance levels of spider mites to organo-phosphates using topical application and slide dip techniques ; laboratory screening tests of alternative acaricides using an O/P resistant strain and a field trial of the screened materials.
1. Strains of Tetranychus urticae were from Timaru (TR), Havelock North (HNR), Lincoln (LN), Germany (GR, GN). Comparisons of the resistant strains and normal strains at the LD50 and LC50 levels were as follows :
(a) Using the topical application technique ; with Parathion, resistant levels of the GR, TR and HNR strains of T. urticae wore respectivuly, 1035, 484 and 452 times as resistant as the LN strain.
(b) Using the slide dip technique ; with Phosdrin, resistant levels of GR, TR and HNR strains of T. urticae were 635.274 and 266 times greater respetively, than the GN strain.
2. The laboratory screening tests were carried out for their contact plus stomach and residual effect to assess the toxicities of eleven alternative materials which would be used for control of O/P resistant strain of T. urticae. The acaricide groups represented were 3 organo-chlorines (Spidex, Kelthane and C 8514), 2 nitrophenyls (UC 19786 and Morocide), 2 cyclic carbonates(Eradex and Mores tan), 1 carbamate (UC20047A), 1 mixture of carbamate and organo-chlorine and 2 other chemicals (C 8677 and M2527). From all acaricide tested, Kelthane and Morocide were the most effective, followed by Spidax and M2527. Morestan, C8514, C8677 and RS 143 were intermediate, but Eradex, UC 19786 and UC 20046A were poor.
3, The number of sapmles required for estimation of the population in the field evaluation of acaricidal effects was chosen as one giving the highest practical precision. It was decided, after preliminary sampling trials, to use samples of 30 leaves per replicate which gave a 5.7% standard error.
4. In the field trials, Morocide applied at the 0.05% and 0.04 % a. i. cone. to black currant trees gave excellent control of O/P resistant population of T. urticae for about 12 days, but Morocide 0.025 and Kelthane 0.02% a. i. conc, gave efficient control for about 6 days. In other words, first applications of Kelthane ane Morocide gave very high degrees of control of O/P resistant population of the two-spotted spider mite. However, the results indicate that secondary application would sometimes be necessary. There was no foliage damage of black currants and strawberries by either acaricides at the concentrations used.
Acknowledgment… The authors are grateful to :
Dr. R. P. pottinger, Senior Lecturer in Agricultural Zoology, Lincoln college, New Zealand, for his helpful assistance in aiding with the organization of thd field work.
Departement of agriculture officers for mite colonies.
Mr. D. A. Slade, Technicol Advisor, Fruitgrowers' Federation (now at Massey Uuiversity) for his assistance and provision of mites for testing.
Mr T. McRae of Timaru for permission to use his crops for field tests.
The following chemical companies and / or their New Zealand agents for so readily supplying samples of acarides ;
Ivon Watkins-Dow Limited.
Fruitgrowers Chemical Company Limited.
Henry H. York & company (New Zealand).
Shell Oil (New Zealand) Limited.