55° was the minimum temperature for PC activity and that 

 75° for 2 or more consecutive days was optimum for 

 migration. Furthermore, he suggested that cool weather 

 following a warm period may reduce or suspend migration 

 until optimum temperatures are reached once again. 

 Lathrop (1) believed that other environmental factors 

 besides temperature may be important to springmigration. 

 Smith and Flessel (4) found that mass migration was 

 correlated with humidity as well as temperature. They 

 indicated that water loss during periods of low humidity 

 may reduce migration. McGiffen and Meyer (2) suggest 

 that low temperatures suppress PC activity and aid in the 

 conservation of resources until daily air temperature and 

 saturation deficits are conducive to flight. They believed 

 that temperature must be above the flight threshold, with 

 saturation deficit below the desiccation range, for migra- 

 tion to occur. 



Because PCs attack border rows first before 

 moving toward the block interior, we recommend only a 

 border row spray early in the season, with a f uli-biock spray 

 at peak PC activity and a border row spray toward ihe end 

 of the PC season. Gulhion and imidan have been the most 

 effective materials against PC. 



Timing of the first border spray is critical and 

 should commence as soon as PC damage is observed on 

 fruit, even if rain is predicted, because PC movement to 

 host trees is likely to commence as soon as the rain slows 

 or stops. The rain may reduce residue longevity, possibly 

 making another insecticide application necessary. How- 

 ever, delay of a spray may leave you with a heavily damaged 

 crop when you awake in the morning! Weigh your choices 

 carefully. 



Over the past 4 years, wc have gathered data to 

 determine the influence of weather on the spring migratory 

 night of PCs from overwintering sites. Ourstudiesindicate 

 that PCs are especially likely to move into orchards during 

 late day or evening hours under humid, warm conditions 

 when the air is relatively calm. Heavy movement occurred 

 even during lulls between intermittent rainfall, especially 

 when the temperature was above 70°F. 



Based on these findings we want to stress the 

 importance of careful daily monitoring of fruit for PC 

 feeding and egglaying, especially when weather conditions 

 are ideal for migration. Examine 5 or 10 developing fruit 

 per tree for fresh feeding or egglaying scars on several trees 

 along rows that border woods. Feeding injury appears as 

 a small round hole, often undercut so that the hole is larger 

 beneath the skin. Oviposition scars are crescent-shaped. 



Our research indicates that during migratory 

 night into an orchard, PCs may use visual and olfactory cues 

 to locate a host tree. However, it appears that odor alone 

 is a stronger stimulus than vision alone. Furthermore, in 

 laboratory studies, we found that host odor aids PCs in fruit 

 location and actually "turns on" feeding behavior. PCs 

 readily locate and feed on sap exuding from cut or wounded 

 branches. We therefore wonder if PCs might be attracted 

 to recently pruned trees. 



Literature Cited 



1. Lathrop, F. H. 1949. Biology of the plum curcuiio in 

 Maine./. Econ. Entomol. 42:12-18. 



2. McGiffen, M.E. and J. R. Meyer. 1986. Effect of 

 environmental factors on overwintering phenomena and 

 spring migration of the plum curcuiio, Coiiolrachclus 

 ^^^(^/^/^/•(ColeopterarCurculionidae). Environ. Enloniol. 

 15: 884-888. 



3. Quaintance, A. L. and E. L. Jenne. 1912. The plum 

 curcuiio. U. S. Dept.Agric. Bur. Entomol. Bull. 103:1-250. 



4. Smith, E. H. and J.K. Flessel. 1968. Hibernal ion of 

 the plum curcuiio and its migration to host trees. J. Econ. 

 Entomol. 61:193-203. 



5. Snap, O. \. 1930. Life habits of the plum curcuiio in 

 the Georgia peach belt. U. S. Dept. Agric. Tech. Bull. 1 88:4- 

 76. 



6. Whitcomb, W. D. 1929. The plum curcuiio in apples 

 in Massachusetts. Mass. Agric. Exp. Sta. Bull. 49:26-52. 



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