I ran a two-way ANCOVA on the data below, in r-studio, to determine whether pupal weights `Pupal.wt` were affected by caterpillars' diet `Trt`, initial weights `Initial.wt`, and the amount of time it took each caterpillar to reach pupation `Larval.period`: `aov(Pupal.wt ~ Trt*Initial.wt*Larval.period, data = GM).`
Is a Tukey HSD test sufficient to follow this analysis?
If so, how can I change either the code or my data to make `TukeyHSD()` work (I get this error message when I try to run it:

   

 > ANCOVA <-aov(Pupal.wt ~ Trt*Initial.wt*Larval.period, data = GM)
> TukeyHSD(ANCOVA)
Error in rep.int(n, length(means)) : unimplemented type 'NULL' in 'rep3'
In addition: Warning messages:
1: In replications(paste("~", xx), data = mf) :
  non-factors ignored: Initial.wt
2: In replications(paste("~", xx), data = mf) :
  non-factors ignored: Larval.period
3: In replications(paste("~", xx), data = mf) :
  non-factors ignored: Trt, Initial.wt
4: In replications(paste("~", xx), data = mf) :
  non-factors ignored: Trt, Larval.period
5: In replications(paste("~", xx), data = mf) :
  non-factors ignored: Initial.wt, Larval.period
6: In replications(paste("~", xx), data = mf) :
  non-factors ignored: Trt, Initial.wt, Larval.period
    
Here's my data:
> str(GM)
    'data.frame':	44 obs. of  5 variables:
     $ Trt           : Factor w/ 2 levels "Infested","Uninfested": 2 2 2 2 2 2 2 2 2 2 ...
     $ Larval.period : int  14 20 18 18 26 14 22 26 20 18 ...
     $ Initial.wt    : num  0.181 0.318 0.218 0.195 0.25 0.181 0.213 0.255 0.236 0.298 ...
     $ Pupal.wt      : num  0.294 0.519 0.527 0.326 0.511 0.299 0.584 0.442 0.481 0.452 ...
     $ X..weight.gain: num  62.4 63.2 141.7 67.2 104.4 ...