4 MASS. EXPERIMENT STATION BULLETIN No. 285 



of pupal development and toughens its body for the hardships of adult life. 

 These summer beetles emerge about August 1 and spend the remainder of the 

 summer in the trees feeding moderately on the maturing fruit. With the approach 

 of cold weather they seek shelter in which to pass the winter. 



METHODS AND EQUIPMENT 



All studies of the life history, seasonal history, and habits of the curculio 

 under normal conditions were made in a screened open-air insectary measuring 

 15 X 25 feet. For most of the work, the insects were confined in glass battery 

 jars 8 inches high and 6 inches in diameter, having 23^ inches of moist sand in 

 the bottom. Glass vials imbedded in the sand supplied water to keep the fruit 

 from wilting during the experiments. Observations were made daily. Records 

 of temperature and relative humidity were secured from a hygrothermograph 

 enclosed in a standard Weather Bureau kiosk. Plum curculios used in the 

 studies were reared in the insectary or collected from infested apple trees early 

 in the season by jarring the adult beetles onto cloth-covered frames. Beetles 

 not under observation were held dormant in an ice che.st maintained at 45° F. 



In 1931, three constant-temperature cabinets became available. These cab- 

 inets are 36 x 36 inches square and 60 inches high, having a frame of oak and 

 being enclosed on all sides by two panes of plate glass with an air space of 13^ 

 inches between the panes. On one side is a door having a pressure slide latch. 

 Refrigeration is supplied from two cooling coils suspended from the top of the 

 cabinets, through which methyl chloride is forced by an electric motor-driven 

 compressor. Heat is supplied at the bottom of the cabinet by a 24-inch electric 

 strip heater which is connected with a small electric fan at the top providing 

 circulation whenever the heater operates. Each temperature unit is connected 

 with a mercury thermostat which insures automatic control. A constant tem- 

 perature within 30 degrees of the outside temperature is guaranteed, and it has 

 been operated successfully between 30 ° and 80 ° F. The usual variation from the 

 desired temperature is about 3° F., since the mechanical equipment allows a 

 deficiency of about 13^° F. above and below the set temperature before the con- 

 trols operate. These cabinets were operated in a greenhouse entry having a 

 cement floor and good ventilation. The glass roof was heavily whitewashed, and 

 split wood curtains provided additional shade from bright sun. No control of 

 humidity was maintained in these cabinets, but frequent readings on psychro- 

 metric equipment showed 65 to 85 per cent relative humidity. In these experi- 

 ments constant temperatures were maintained at 55°, 65° and 75° F., while a 

 fourth constant of 85° F. was obtained in a 110-volt, 150-watt electric incubator 

 having a glass door. 



In these cabinets the beetles were confined in battery jars as in the insectary 

 studies. 



The spray solutions were applied to the apples in the laboratory through a 

 mist nozzle delivering 12 gallons per hour under 30 pounds air pressure. The 

 apparatus was similar to that used by Miller (5) in Ohio, except that the air 

 pressure was supplied through an auxiliary pipe from a large compressor which 

 was in operation in the building. With this equipment the amount of spray 

 delivered was constant for any unit of time. The apples were thoroughly wet 

 without dripping, and this usually required two complete turns with a separate 

 wetting of the blossom and stem end. A supply of apples for a week was sprayed 

 at one time and the stems of these apples were placed in water in a refrigerator 

 until they were used. 



