This paper reports the within-plant distribution of cabbage looper on cotton through time. Mainstem leaves receive the largest percentage of eggs. Increased plant density results in a greater proportion of eggs being oviposited on mainstem leaves, and closer to the mainstem terminal. As the plants age and increase in size, the eggs are found higher on the plant. The larvae appear to prefer leaves 5 to 10 nodes from the terminal. The average age of leaves being consumed by cabbage looper is estimated. A sampling plan for cabbage looper eggs based on mainstem leaves for estimating the optimal sample size for a given level of reliability is presented, taking into account plant age, plant density, and sampling cost (time).