Distribution Pattern and Sequential Sampling Plan for the cotton bollworm in sorghum.

Abstract

The cotton ballworm (Heliothis armigera hubner) is the important insect attacking sorghum especially in teh seed setting and milky stages. The outbreak incidence including efficient sampling plan is much necessary for controlling. The study on the distribution pattern pattern and sequential sampling plan of cooton ballworm in sorghum were conducted durinhg the years, 1989-1991. The KU 439 variety was planted using 75x10 cm spacing in a 1600 m plot at the National Corn and sorghum Research Center, Nakornrachasima province. The number of larvae and their development stages on every sorghum head during the seed setting and milky sytages were recorded. In each year the data showed that the number of larvae in milky stage was much higher than that in setting stage. As for several insect infestation situations, the observed data are most reasonably described by the negative binomial typ eof distribution. Using the value from the negative binomial fit for milky stage, economic injury level = 1 for the lower level which no action is needed and = 2 for the hgigher level which insecticide should be applied, also using error I = error II levels of 0.05, a sequential sampling plan has been constructed. Hence a graph of 2 paralleled lines represented 2 equations separate the area for decision making into 3 zones. The first zone for insecticide appplication necessity if the accumulative number of ball worm is more than 1.4038n+13.4386 when n sorghum plants are examined. The second zone that insecticide application is not necessary if the accumulative number of ballworm is less than 1.4038n-13,4386 when n sorghum plant are examined. further examination should be done if the accumulative number of ballworm larvae is in between the 2 mentioned zone from n sorghum plants.