32 MONTANA EXPERIMENT STATION BULLETIN 333 



dormant summer spray oils should be used only in the event 

 liquid lime sulphur cannot be obtained, as they appear to be 

 less efficient under Montana conditions. 



Yellow Jackets (Vespidae) appear in cycles. In 1933 ap- 

 parently there were none. In 1934 there were quite a number 

 but they appeared too late to damage the fruit crop appreciably. 

 The season of 1935 saw considerable damage to the cherry and 

 berry crops by yellow jackets. Early in 1936 "queen" yellow 

 jackets were numerous. As the season advanced these ceased 

 to appear, which is normal, but "worker" yellow jackets failed 

 to appear in their place as is usual, only an occasional one being 

 seen all season. 



Undoubtedly there is some natural force which checks the 

 yellow jackets after they have increased over a three-year 

 period. In 1935 a few tests with fly traps and poisoned baits 

 established the fact that they preferred ground meat, such as 

 liver, to fermented fruit or fresh fruit, such as cherries. This 

 factor might be used in drawing them away from feeding on 

 ripe berries or cherries. Sodium arsenite failed to function as 

 a poison as it repelled the wasps from the bait. Baghouse 

 arsenic baits gave a high per cent of kill. Considering all 

 angles the poisoned bait or fly trap is much too slow a pro- 

 cedure for wasp control once they start attacking the fruit. 



Other Orchard Insects 



New orchards, especially those planted on newly cleared 

 land, are often seriously defoliated by a number of species of 

 leaf-feeding insects. Probably the most important of these are the 

 pear and cherry slug (Eriocampoides limacina Retz.j, and other 

 undetermined slug feeding on cherry leaves, both of which made 

 their appearance for the first time in the Flathead Valley this 

 year. The former attacks the upper surface of the leaf, is very 

 dark green, enlarged at the head end and holds the tail end up 

 from the surface of the leaf. The latter (figure 5) attacks the 

 lower surface of the leaf, is very pale green, tapers from head 

 to tail, and does not hold the tail end erect. Tests during 1935 

 gave nearly 100 per cent control with contact sprays and dusts, 

 stomach poison sprays and dusts, and hydrated lime as a dust. 

 Even ordinary road dust gave 75 per cent control. With this 

 evidence a slug infestation appears to be caused chiefly by 

 neglect or lack of knowledge on the part of the orcharist. 



