  We have searched Microvariability and Oscillations of STars (MOST) satellite
photometry obtained in 2004, 2005, and 2007 of the solar-type star HD 209458
for Trojan asteroid swarms dynamically coupled with the system's transiting
"hot Jupiter" HD 209458b. Observations of the presence and nature of asteroids
around other stars would provide unique constraints on migration models of
exoplanetary systems. Our results set an upper limit on the optical depth of
Trojans in the HD 209458 system that can be used to guide current and future
searches of similar systems by upcoming missions. Using cross-correlation
methods with artificial signals implanted in the data, we find that our
detection limit corresponds to a relative Trojan transit depth of 1\times10-4,
equivalent to ~1 lunar mass of asteroids, assuming power-law Trojan size
distributions similar to Jupiter's Trojans in our solar system. We confirm with
dynamical interpretations that some asteroids could have migrated inward with
the planet to its current orbit at 0.045 AU, and that the Yarkovsky effect is
ineffective at eliminating objects of > 1 m in size. However, using numerical
models of collisional evolution we find that, due to high relative speeds in
this confined Trojan environment, collisions destroy the vast majority of the
asteroids in <10 Myr. Our modeling indicates that the best candidates to search
for exoTrojan swarms in 1:1 mean resonance orbits with "hot Jupiters" are young
systems (ages of about 1 Myr or less). Years of Kepler satellite monitoring of
such a system could detect an asteroid swarm with a predicted transit depth of
3\times10-7.
