Effects of bark girdling on carbohydrate supply and resistance of loblolly pine to southern pine beetle (Dendroctonus frontalis Zimm.) attack

Importance of current photosynthate in the regulation of tree defense against the southern pine beetle (SPB),Dendroctonus frontalis Zimm. (Coleoptera: Scolytidae) was investigated in loblolly pine,Pinus taeda L. Downward translocation of carbohydrate was blocked by removing a ring of bark (girdle) at 3.5 m above ground. Beetle colonization success and tree defensive responses measured as resin flow and induced lesion formation to inoculations with the beetle-associated fungus,Ophiostoma minus (Hedge.) H. and P. Sydow., were assessed above and below girdles. We hypothesized that a decrease in a available carbohydrate would lead to a decrease in tree defense and an increase in SPB colonization success below girdles. At 2 weeks, post-girdling carbohydrates were already reduced by 50% below girdles, but no significant differences in beetle colonization success or defensive responses were measured. At 8 weeks, post-girdling starch was reduced by 93%, sucrose by 44% and resin flow by 44% below girdles. Southern pine beetle adults were more successful in colonizing areas below than above girdles. However, no significant differences were detected in the size of the lesions that formed in response to inoculated fungi. This suggests that the size of the induced lesion may not be a reliable indicator of tree resistance to bark beetle attack as previously believed, and that lesion development is not entirely dependent on available carbohydrate or related to tree defense against beetles. Cambial growth was reduced below girdles with no latewood formed below and 25 rows of latewood formed above girdles. Latewood contains much higher densities of resin ducts than earlywood. This may explain why resin flow was lower and beetles were more successful in colonizing areas of the tree below girdles. Therefore, tree defense against bark beetles may be more complex than a simple supply-and-demand relationship for carbohydrate, and changes in source-sink relationships, as influenced by the environment, may be more important than supply.     

Early Growth and Survival of Larval Alligator Gar,Atractosteus spatula,Reared on Artificial Floating Feed with or without a Live Artemia spp. Supplement

Alligator gar, Atractosteus spatula, are a new aquaculture species with many aspects about rearing unknown. Alligator gar are cannibalistic during their larval stage and methods to minimize cannibalism should be developed to increase overall survival. Growth and survival were determined for larvae fed pelleted floating food only or fed pelleted floating food supplemented with live Artemia spp. nauplii for the first 7 d of exogenous feeding (5 d after hatching [d.a.h.] to 12 d.a.h.). Total length, weight, condition, and specific growth rate (SGR) was determined at 12 and 20 d.a.h. Fish supplemented with Artemia were larger by 12 d.a.h. and continued to be at 20 d.a.h. than fish fed only floating food. SGR was higher at both 12 and 20 d.a.h. for fish that received the Artemia supplement. Survival was higher for fish supplemented with Artemia (71%) than for the floating food only treatment (43%). Cannibalism was the primary cause of mortalities and was higher in fish fed floating food only (44%) compared to Artemia supplemented fish (19%). Artemia may elicit a stronger feeding response and improve acceptance of pelleted floating foods. Results suggest an improved feeding regime compared to previous feeding regimes used in rearing larval alligator gar.