  In the framework of our narrow-band survey of the Local Group galaxies, we
present the results of the search for planetary nebulae (PNe) in the dwarf
irregular galaxies IC10, LeoA and SextansA. Using the standard on-band/off-band
technique, sixteen new candidate PNe have been discovered in the closest
starburst galaxy, IC10. The optical size of this galaxy is estimated to be much
larger than previously thought, considering the location of the new PNe in an
area of 3.6 kpc X 2.7 kpc. We also confirm the results of previous studies for
the other two dwarf irregular galaxies, with the detection of one candidate PN
in LeoA and another one in SextansA. We review the number of planetary nebulae
discovered in the Local Group to date and their behaviour with metallicity. We
suggest a possible fall in the observed number of PNe when [Fe/H]$<<$-1.0,
which might indicate that below this point the formation rate of PNe is much
lower than for stellar populations of near Solar abundances. We also find
non-negligible metallicity effects on the [OIII] luminosity of the brightest PN
of a galaxy.
