Volume 39, Issue 2
February 1954, pages 37-90
pp 37-43 February 1954
Using DDT dust as insecticide and third and fourth instar larvæ ofEuproctis lunata Walk. as test insect the following fundamental aspects of the bioassay of stomach poisons have been investigated.
Starvation and resistance.—It has been indicated that, contrary to previous notions, resistance of E. lunata larvæ decreases with increase in period of starvation. The apparent increase in resistance due to starvation is obviously due to the fact that prolonged periods of starvation (24–48 hours) make theE. lunata larvse somewhat lethargic and these lethargic larvæ actually eat lesser quantity of both poisoned and unpoisoned food and therefore their percentage mortality is also low.
Body weight and resistance.—It has been shown that resistance to insecticide increases with increase in body weight. An increase in amount of poisoned sandwich eaten with increase in body weight has been observed, but the amount of poison ingested per gm. body weight of insect varied within a comparatively narrow range and showed no definite order of variation. It has been suggested that more or less constant amount of DDT per gm. body weight begins to have an inhibitory effect on further feeding.
Several smaller doses versusone large dose.—It has been shown that a comparatively larger dose given to larvae in one instalment is more effective than the same dose given in several instalments of smaller doses. It is suggested that the detoxification of some of the poison may be the cause of this phenomenon.
pp 44-50 February 1954
The susceptibility of rice plants of different ages toHelminthosporium disease was studied by conducting artificial infection tests on three different dates during the season. Three varieties, 2 susceptible and a resistant were included in the study. It was found that the susceptibility increased with age of plants and the relative susceptibility of varieties, as compared between plants of the same age remained the same at any time during the season. Inoculations carried out in September produced the maximum infection.
Susceptibility to Blast disease at different ages was studied in 2 field experiments. It was found that younger plants were most susceptible and the resistance increased as the plants grew older. Only the post-planting age of the plants had an effect on their susceptibility.
pp 51-75 February 1954
pp 76-90 February 1954