Mantellas are small terrestial frogs from the island nation of Madagascar.  These frogs used to be found all over the island, but extensive logging and agriculture has destroyed much of their habitat.  Captive breeding of this species may be the only chance to save this frog from endangerment and extinction. 
Background Information
Mantellas are not a tropical heat loving species, as many people believe.  Out of the 11 or so species identified, only a couple tolerate high temperatures (80F).  Many of the species commonly kept in captivity are montaine, and enjoy lower temperatures (70F) with high humidity.  I am definitely not an expert on the subject, so I can only give reliable information on the species I have kept and/or breed.  Those include:  m. expectata, m.aurantiaca (gold&red), m.baroni, and m. cowani. 
aurantiaca, red morph
Feeding mantellas isn't so hard.  Most are aggressive eaters, and will readily take almost anything they can stuff in their mouths.  (On that note:  Be careful not to give them anything too big.)  Fruitflies, crickets (up to 1/2 in), mealmoth larvae and adults, flour beetle larvae, and meadow plankton.  Prey items should be dusted with calcium and vitamin supplements at least once a week, and more often during breeding cycles.  I recommend feeding them 2-3 times per week on average, and more often when trying to induce breeding. 
Terrarium Size:  I like to dedicate 3-5 gallons per frog. 

Temperature:  68-78F is ideal.  DO NOT ALLOW TEMPS TO GO ABOVE 80F!

Humidity:  About 70-80%

Lighting:  Full spectrum lighting is not neccesary but helpful for plant and moss growth. 

Breeding requires a cycling of a simulated dry season followed by a wet season.  During the dry season, tanks should only be misted enough to keep the frogs from drying out.  Feeding sholuld also be reduced to twice a week.  Lighting can also be reduced to 10-12 hours.  After about a month, it is time to simulate a wet season.  Mist the tanks daily, and supply food on a daily basis also.  They will often try to grasp each other in amplexus upon feeding and/or misting.  Lighting can be increased to 14 hours.  Egg laying sites can be hard to find.  They like to lay at night or in the twilight hours in dark, moist places near water.  I have placed baby food jars under moss near the waters edge and gotten some success.  They will also lay on or under leaves and plants.