Many of the most expensive legislative races in the state are being waged in southeast Michigan but few political observers could have anticipated that the fiercest competition in terms of TV ads would take place in a Macomb County Senate district.

The costliest TV campaign is centered in the 10th District, where Democratic state Rep. Henry Yanez (above, right) is facing off with Republican newcomer Mike MacDonald (above, left). So far, the Democratic and Republican parties have spent a combined $498,000 on campaign commercials – on broadcast or cable television — to promote their candidate or slam the opposition, according to the Michigan Campaign Finance Network (MCFN).

The battleground features a vacant seat as the incumbent, Sen. Tory Rocca, is term-limited. The district includes three of Michigan’s largest suburban communities – Sterling Heights, (most of) Clinton Township and Macomb Township..

The district has a voter base that’s 55 percent Republican, 45 percent Democratic. But the GOP failed to recruit a big-name candidate so MacDonald, a first-time contender with few political connections at the time, emerged from a weak field in the August primary. The Macomb Township Republican began his general election campaign as an underdog while Yanez seemed ready to flip the seat for the Democrats in a campaign season where the party already has momentum.

MacDonald soon got pummeled by Democratic Party advertising that recounted his conviction in 2007 for severely injuring a motorcyclist while driving drunk. The victim suffered several major injuries in the early morning crash and had his left leg amputated below the knee. MacDonald served 12 months of probation and paid a $32,500 court settlement to the injured party.

Beyond TV spots, the Democrats relentlessly posted video ads on Facebook about MacDonald’s drunken driving incident, which ran from mid-September until earlier this month.

For his part, MacDonald, a financial adviser, has emphasized his National Rifle Association membership and his endorsement from the Michigan Manufacturing Association. Both candidates have relied heavily on the two parties to run their campaign advertising operations. According to the latest campaign finance reports filed with the state on Aug. 27, Yanez had spent $45,000 and had $93,000 left in the bank. MacDonald had spent $21,000 and had a $1,500 balance.

Overall, with about three weeks remaining until Election Day, an estimated $4.3 million in TV ads have already aired in races for the Michigan Legislature. That’s based on television advertising figures analyzed by MCFN, a nonpartisan watchdog group.

The two parties rely heavily on wealthy donors, PACs and nonprofit groups to build up their campaign war chests.

The majority of the money, about $2.4 million, has gone to ads about House and Senate candidates running in just four counties in southeast Michigan – Macomb, Oakland, Wayne and Monroe. As Democrats push to make gains in suburban areas nationally, consultants associated with both parties believe the area outside of Detroit could be a key battlefield in the fight for control of the state House and state Senate in November.

Of the five state Senate races that have attracted the most ads so far, three are in suburban Detroit.  And of the five state House races that have attracted the most ads so far, four are in those same Detroit suburbs.