Studies on the effect of the mixture of line sulphur and zinc sulphate upon the Arrowhead Sca_??_e

Abstract

The arrowhead scale, Prontaspis yanonensis KUWANA, is one of the most nacious insec's of citrustrees in Japan. For its control the mixture of lime sulphur and zinc sulphate Las hitherto been applied by citrus growers, resulting in the rapid decrease of the pest. With a view to making out the effectiveness of the said mixture, some series of experiments have been carried. out with the results, as given in the summary that follows. 1. So far as concern laboratory and field experiments carried out in order to test the effect of the mixture of lime sulphur and zinc sulphate on the arrowhead scale, the mixture exercises scarcely effect on the adult. However, the newly hatched larva, though capable of infesting the sprayed leaf of five-years-old tangerine tree only at about 1% against about 40% on the unsprayed leaf, becomes before long to fall bown dead, without causing any trace of growth. This state of thins holds not only good in the field observation, but also in the experiment with the leaf washed the mixture off. Judging from the facts just mentioned, it is selfevident that the mixture acts as an evasive factor for the attachment of larva on the one hand, ani affects the larva on the other, permeating the leaf tissue. 2. Nevertheless the entire absence of change in the leaf tissue dealt with either of zinc sulphate and lime sulphur, the pH value in the tissue dealt with the mixture is rapidly increased for the first 10 days to attain 7, and then gradually decreased to about 5.8, or the normal state.. These facts appear to point to that the mixture is capable of permeating the leaf tissue, differin_??_ from either of zinc sulphate and lime sulphur. 3. Taking into consideration the fact that the pH is weak acidic in zinc sulphate and alkaline in lime sulphur, it may be stated that the element exercising the change of the value is attributable to the latter. For the purpose of determining this respect, some series of quantitative analysis and mechanical observation were carried out with the results as follows: the amount of sulphur in the sprayed leaf is about twice as much as that in the unsprayed, and sulphur is mainly deposited in the cortical tissue. Consequenily it may be said that sulphur acts as an element playing an important role in the changte of pH. 4. On accout of, application of zinc spray for its efficiency in the citrus plant, it is appropriate to presume that sulphur is capable of permeatin: the leaf Tissue with the aid of zinc, , nevertheless the entire absence of permeability. 5. On the presumption that the main element of the mixture is zinc sulphide and that it affects the larva, permeating the leaf tissue, some series of experiments were prosecuted with this compound extracted from the mixture, as well as with that for sale. As the results, it is revealed that the former, though more inferior as compared with the mixture, is still effective, , but the latter is not effective at all. Subsequently presuming that the uneffectiveness of the latter may be due to dryness, another series of experiments were made with zinc sulphide ob_??_ained by reacting sulphurated hydroeen upon zinc sulphate, devoid of dryness, and it was revealed that the said compound was effective in as much as the mixture, notwithstanding the entire loss of efficacy immediately after it was dryed at high or low temperature. Consequenly it may be concluded that zinc sulphide permeates the leaf tissue in the course of reaction of lime sulphur and zinc sulphate. 6. So far as experiments go, the mixture exerciss such lethal actions as in the following: 1) Besides its evasive action for the attachment of larva to the leaf, the mixture is of a contact insecticidal action especially at an early stage of larval life. 2) A close microscopic observation reveals that the larvae, exclusive ofa few, are found dead without insertin_??_ suckers into the leaf tissue