2-6 wks after petal fall (depending on the year). Stages 

 1-9 were considered as pre-petal fall, whereas stages 

 10-11 were post-petal fall. 



Calculating Thermal Constants. Thermal 

 constants for the initiation of PC iiTiinigration (START), 

 and the 50* and 80* percentiles of cumulative captures 

 were estimated using a temperature threshold of 43°F 

 for the resumption of adult PC activity after 

 overwintering. On each trapping year. Degree Days 

 started to accumulate on January 1 . 



Relative Predictability of PC Immigration: Tree 

 Phenology versus Thermal Constants. To determine 

 whether the onset of immigiation was better explained 

 by accumulation of Degree Days or by tree phenology, 

 two coefficients of variation (CV) were constructed. A 

 coefficient of variation is a relative measure of 

 variability (it uses the standard deviation [SD]) around 

 a mean value, therefore a low CV (relative to the other 

 CV estimated) suggested greater reliability of the 

 particular method used to predict onset of PC 

 immigration. Our first CV involved mean thermal 

 constants (using the mean DD and SD obtained across 

 the five trapping years), whereas the second CV 

 involved the particular phenological tree stage at which 

 PCs started immigrating into the orchard block (using 

 the mean and SD of the numerical codes used on each 

 year). 



Results 



Overall pattern of PC immigration, hi all, 4,279 



PCs were captured by traps across all five trapping 

 years (Table 1). On average, the entire period of PC 

 immigration lasted 63 days, with the shortest and 

 longest periods encompassing 5 1 days in 2000 and 85 

 days in 2002, respectively. The earliest start of PC 

 immigration occurred in 2002 (on 14 April), whereas 

 the latest start of immigration took place in 2001 (on 2 

 May). PCs started immigrating when trees were either 

 at the silver tip stage (stage 1) (in 2004), at the tight 

 cluster tree stage (stage 4) (m 2000, 2002, and 2003) 

 or at the first pink tree stage (stage 5) (in 2001). Fifty 

 percent cumulative captures occurred when trees were 

 either in full bloom (stage 8) in 2000 and 2001, by 

 petal fall (stage 9) in 2003 and 2004, or during the first 

 week of fruit development (stage 10) in 2002. Eighty 

 percent cumulative captures took place during stage 

 10 (i.e., first week of fruit development) in four of the 

 five years (2000-2003) or during stage 11 (i.e. after 

 one week of fruit development) in 2004. 



Table 1 shows that of the total number of PC 

 immigrants captured by traps (potentially colonizing 

 host trees), on average, 59% have already done so by 

 petal fall, with the remaining 41% being captured by 

 traps after petal fall. A statistical test revealed that 

 numbers of PCs being captured by traps before and 

 after petal fall differed significantly across years. The 

 period of time required from the last day of petal fall 

 to achieve 80% cumulative PC captures was one week 

 in 2000 and 2004, two weeks in 2003, and three weeks 

 in 2001 and 2002. 



Relationships among trap captures, tree 



Fruit Notes, Volume 69, Fall, 2004 



