10 MASS. EXPERIMENT STATION BULLETIN 373 



rate, in relation to the activity at 70° and 80° F., than it does in the case 

 of the Cryptolaemus. 



FEEDING OF CRYPTOLAEMUS LARVAE ON EGGS OF CITRUS 

 MEALYBUG AT CONSTANT TEMPERATURES 



Since temperature and liumidity had been found to be the most im- 

 portant controlling factors in the development and activity of the Crypto- 

 laemus, an attempt was made to determine in more detail tiie effect of 

 temperature on the feeding and growth of the larvae. 



Equipment and Methods 



The temperature controls used in this work were especialh' constructed 

 cabinets containing about 20 cubic feet. The sides were double glass 

 with one inch air space to increase insulation and to admit sufificient light 

 to permit plants to grow reasonably well. Split-wood blinds on rollers 

 shaded the cabinets and control apparatus from direct sun on clear days, 

 and the doors were closed with refrigerator door latches. The temper- 

 ature was controlled by means of an air thermostat of the bimetal type 

 with a double mercury-tilt switch. Refrigeration was supplied from 

 coils hung from the top of the cabinet tiirough which methyl chloride was 

 forced by an electrically operated compressor, and heat was supplied 

 from an electric strip heater aided by a small electric fan. This apparatus 

 controlled the temperature within a 3° differentia] when operated within 

 30° of the air temperature. 



No humidity control was available. In 1935, pots of moist soil provided 

 a fluctuating humidity between 30 and 60 percent whicli averaged higher in 

 tlie cooler operated cabinets than in the warmer ones. In 1937, pans of 

 water were supplied in each cabinet, which provided a slightly Iiigiier 

 relative humiditj' which undoubtedly influenced the records to a small 

 extent. 



To obtain larvae for tlie feeding records eggs were collected in the 

 greenliouse and in the rearing cages and placed in glass tubes filled with 

 plaster of Paris and resting on moist sand (11). When the larvae hatched, 

 they were removed with a camel's-hair brush to a gardenia leaf in a jelly 

 glass. Five mealybug eggs, taken from a fresh egg mass, were also placed 

 on the leaf. One Cryptolaemus larva was placed in each jelly glass and 

 tlie trays of glasses were placed in the temperature control cabinets. Ten 

 larvae were used at each temperature in each series of experiments. 

 Considerable mortality resulted, especially when the larvae were small — 

 generally due to unavoidable injury in handling — and when a larva died, 

 it was immediately replaced with another newly hatched specimen. As 

 soon as the larvae became acclimated to the jelly glass cages, generally 

 in about ten days, about an inch of moist sand was placed in each jelly 

 glass and this was moistened when the daily observations were made. 



In determining the number of mealybug eggs eaten, the leaf, the body 

 of the larva, and the sides and bottom of the jelly glass were carefully 

 examined under the binocular microscope and the number of eggs found 

 was subtracted from the number placed on the leaf the previous day. 



The number of eggs supplied daily was calculated to equal or slightly 

 exceed the number which the larva would eat, and in most cases the 



