Migratory flight potential and the role of juvenile hormone in flight regulation in the western corn rootworm
Analysis of data from two separate studies detail trivial and migratory flight potential and correlate both the role of juvenile hormone (JH) and reproductive development with flight activity in western corn rootworm, (WCR), Diabrotica virgifera virgifera LeConte. Field-captured and laboratory reared, mated females (n = 183), aged 2-15 post-emergence, were flown on flight mills linked to a microcomputer data-recording system. Flight duration ranged from 1 to 17 min for trivial flights while sustained flights of 30 min or more lasted up to 4 h. Sustained flights were not made after females were 9 days old. Maximum distances of 24 km for one flight and 39.6 km for all flights during a 24-h period were recorded. Average speed of flight was 16 m/m for trivial fliers and 50 m/min for sustained fliers. Periodicity was observed for both types of flight; greatest flight activity occurred from 1800 to 2400 hours. Sustained flights were classified as migratory. A possible mean migratory distance of over 200 km during the first week of a female adult's life was calculated. Realistic appraisal of dispersal capabilities in this species should include assessment of the additional displacement affected by prevailing winds in the Midwest;The second study focused on the role of JH in regulation of flight activity in the WCR. Changes in the level of juvenoid compounds (i.e., JH-type) in adult mated and virgin females were accomplished through (1) the topical application of a JH agonist or mimic (JHM, methoprene), or (2) the topical application of a JH antagonist (AJH, fluoromevalonate), which inhibits synthesis of JH. Of 468 females tested, 252 females flew and migratory flight behavior was observed for 145 (31%). No migratory flights were undertaken by untreated virgins. While JHM- and AJH-treated females flew both trivial and sustained flights which were significantly longer in duration and distance over controls, age displacement of peak flight activity varied according to treatment and mating status. There seems to be a definitive window of migratory flight activity in the WCR that can be temporally displaced by JHM and AJH treatment. Ovarian development was negatively correlated with migratory flight activity which substantiates the inverse relationship between flight and reproduction. JH moderates the considerable flight capabilities of the WCR, permitting adaptation of this species to a dynamic, agricultural, ecosystem.