One might speculate that damage to crop trees in plots having fewer trees per acre 

 might have been the result of a given number of weevils per unit area concentrating on 

 fewer trees. However, other circumstances are known where weevils apparently preferred 

 a more open or less shaded environment. Magdalis perforatus are most abundant in 

 young, open plantations in Ontario, Canada (Martin 1964). The white pine weevil, 

 Pissodes stvobi (Peck), avoids understory white pines because of the effect of shading, 

 rather than because the trees are small (Harman and Kulman 1969). 



Weevil Damage and Time of Thinning 



Perhaps the most critical factor determining whether crop trees in thinned areas 

 will be damaged--and to what extent--by Magdalis adults is the time of year stands are 

 thinned. Examinations of 45 thinned areas 3 over a 4-year period indicated that: 

 (1) Crop trees in areas thinned before late July usually suffered moderate to heavy or 

 heavy Magdalis damage; (2) if thinnings were completed early in August, light or light 

 to moderate damage might still occur; and (3) crop trees in areas thinned after mid- 

 August usually will have only occasional needle feeding or will not be damaged in that 

 year. The 45 thinned stands, arranged in a 3 by 3 contingency table by thinning time 

 and degree of damage, were subjected to a test of independence (Snedecor 1956). The 

 calculated chi-square value substantiates the conclusion that the degree of Magdalis 

 damage in thinned stands is highly dependent on the time of year stands are thinned. 



The proximity of thinned areas further indicates the importance of time of thin- 

 ning in predicting the intensity of damage to crop trees that can be expected. Many 

 of the thinned areas shown in figure 10 (letters merely designate the cutting units) 

 are only a hundred yards or so from their nearest neighbor; yet time of thinning in 

 any area had no influence on the intensity of damage in any other area. For example, 

 units N, 0, P, Q, which were thinned in late July, were heavily damaged; yet weevils 

 only lightly damaged crop trees in unit S, which was thinned in early August. Moreover, 

 crop trees in unit L, which was thinned after mid-August, were undamaged. 



Though crop trees in thinnings completed after mid-August usually do not become 

 infested or experience only occasional needle feeding that year, slash from thinnings 

 completed in early October or later usually is soon covered by snow (especially at 

 higher elevations) and sometimes remains attractive to weevils the following spring. 

 In late summer of 1968, I examined crop trees in four areas that had been thinned in 

 early October of the preceding fall. In all areas, I found light weevil damage to the 

 1968 foliage. Two of these areas (D, M) are shown in relation to other thinned areas 

 in figure 10. Usually, however, slash in areas thinned in early October or later-- 

 especially at lower elevations and/or on southern exposures- -will deteriorate by the 

 following spring or early summer and no longer be attractive to weevils. 



During the period of study, adult Magdalis gentilis were flying and were attack- 

 ing crop trees in thinned areas usually during late June and early August. 



^Of these, 43 were thinned using portable rotary thinning saws. Two were thinned 

 using a Marden Brush Cutter, a huge cylinder equipped with cutting blades pulled over 

 the trees by a bulldozer (manufactured by the Marden Mfg. Co., Auburndale, Florida). 



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