The only non-toxic way I can think of is to slowly vent an antire cylinder of dry Nitrogen gas (not toxic, but displaces oxygen) into the sealed car and hope it displaces enough oxygen to kill them off. Otherwise maybe those ultrasonic pest devices may work, but I haven't tried or investigated them.

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John

2003 Firemist Red/grey leather SL 500
2015 Palladium Silver/black mbtex GLK 350
1987 Smoke Silver/burgundy mbtex 300E Sportline (SOLD)

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