Host Selection in the Douglas-Fir Beetle Following Extended Periods of Flight: The Effect of Depleted Fat Reserves on Pioneer Behavior

Publication Date


Type of Culminating Activity


Degree Title

Master of Science in Biology



Major Advisor

Ian C. Robertson


Fat reserves are the main fuel source for long durations of flight in insects. Calculating fat loss as a function of flight can be problematic because quantification of fat requires destructive analytic techniques, such as Soxhlet extraction with petroleum ether. Therefore, to assess fat loss in individuals, estimates of initial fat content must be made prior to flight. I used externally-measured variables and AIC to select the best model among 12 candidates in an attempt to predict initial fat levels in females of the bark beetle D. pseudotsugae. The best model contained the parameters of body condition scores (residuals of mass/volume relationship) and density of developing brood (measured as the number of emerging adults per surface area), both of which had significant positive effects on the percentage of fat in newly emerged beetles. Average amount of fat in newly emerged female beetles was 14.1% of their dry mass. Rotary flight mills were used to determine the relationship between flight and fat reserves. First, estimates of beetles' initial fat reserves were made. Then, female D. pseudotsugae were assigned flight treatments ranging from 90 - 1380 minutes. Through using Soxhlet extraction to quantify fat levels following flight treatments, I found that every hour of flight approximately decreased the percentage of fat by one. However, the effect of flight on fat reserves was not significantly different than periods of non-flight activity, most likely because individuals spent 50% of their time in non-flight activity. Individuals with high estimates of initial fat content were stronger flyers, as measured by the percent time in flight activity and hourly flight velocity. Using a combination of initial estimates of fat reserves, time in flight, and time in non-flight, it is now possible to experimentally decrease fat reserves in D. pseudotsugae, remove them unharmed from flight mills, and subsequently test for behavioral changes. Fat content and fat loss via flight can now be included as factors in behavioral tests examining such phenomena as host or mate selection.

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