tmpar <- par( mar = c(3,3.1,0,0), mfrow = c(1,2) )
on.exit( { par( tmpar ) ; rm( tmpar ) } )

tmpq <- 1:50
mplot( wasp$Gres[tmpq], wasp$Hres[tmpq], wasp$caste[tmpq], xlab ="", ylab = "" )
mlines( wasp$Gres[tmpq], predict( wasp.covr )[tmpq], wasp$caste[tmpq],
   lty = 2 )
mlines( wasp$Gres[tmpq], predict( wasp.covwr )[tmpq], wasp$caste[tmpq],
   lty = 1 )
mtext("head residuals",2,2)
mtext("(a) gonadium residuals for queens",1,2)

tmpq <- 51:100
mplot( wasp$Gres[tmpq], wasp$Hres[tmpq], wasp$caste[tmpq], xlab ="", ylab = "" )
mlines( wasp$Gres[tmpq], predict( wasp.covr )[tmpq], wasp$caste[tmpq],
   lty = 2 )
mlines( wasp$Gres[tmpq], predict( wasp.covwr )[tmpq], wasp$caste[tmpq],
   lty = 1 )
mtext("head residuals",2,2)
mtext("(b) gonadium residuals for workers",1,2)