EXERCISE 64 



THE LIFE HISTORY OF AN INSECT 





7^ 



Cabbage worm or larva of the 

 cabbage butterfly 

 Dorsal and lateral view. (After Dean) 



Fig. 94. 



Statement. Before we can control insects we must learn something of their life history ; that is, when 

 and where they lay their eggs, when the eggs hatch, into what forms they develop, what they feed upon, 



where and in what stage they pass the winter, and how many gener- 

 ations are produced each year and what their natural enemies are. 



Object. To study the life history of the cabbage worm. 



Materials. A flowerpot for each student in which a young 

 cabbage plant is growing ; a lantern globe, the top of which has 

 been covered with cheesecloth ; a number of breeding cages large 

 enough to hold several of the potted cabbage plants ; insect nets 

 and cans or jars. 



Directions. 1. A few days after the cabbage is set in the spring observe the white butterflies 

 with black spots on the wings, which may be seen flying about near the ground. Observe how and where 

 their eggs are deposited. Describe the eggs. With the 

 insect net capture mating pairs of the butterflies and 



place each pair in a jar or can 

 so they may be taken unin- 

 jured to the laboratory. In 

 the laboratory one pair should 

 be placed in each of a number 

 of breeding cages. The pots 

 containing the young cabbage 

 plants can be placed in the 

 cages and daily observations 

 made for the presence of eggs. 

 Make notes and drawings of 

 where the eggs are deposited, 

 how they are grouped, their color, size, and shape. 



2. After the eggs hatch, the potted plants should be removed from the breeding cage and the 

 large lantern globe, the top of which has been covered with cheesecloth, should be placed over each 



plant to prevent the escape of the larvae. Make notes and draw- 

 ings describing the newly hatched larva, showing the number of 

 molts and the length of time in the larval stage. If possible, observe 

 the transformation of the larvae to the pupal form. 



3. After pupation the pupae that are wanted for immedi- 

 ate use should be placed in a light, warm room, where they will 

 probably emerge in a few days. Determine and make notes of I 

 date and method of emergence. Describe the adult. 



Questions. What are the feeding habits of larvae? Will the 

 arsenical sprays kill them ? When and how often should the sprays 

 be applied? Is it practical to hand pick the larvae from young 

 plants ? Where and in what position are the eggs laid ? 



References. Waters, H. J. Essentials of Agriculture, pp. 300-312. Ginn and Company. Sanderson, 

 W. Insect Pests of Farm, Garden and Orchard. J. Wiley & Sons. Farmers' Bulletin 766, United States 



Fig. 95. Pupa or chrysalis of 

 the cabbage butterfly 



Dorsal and lateral view. (After 

 Dean) 



FlC 



96. Cabbage plant injured by the cabbage 

 (After Dean) 



Fig. 97. Cabbage butterfly (Pontia rapes) 



on cabbage leaf 



(After Dean) 



Department of Agriculture. 



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