Below is an excerpt on the maturity of worms after a drug has been introduced.

Proc Biol Sci. 2007 June 22; 274(1617): 1465–1466.
Published online 2007 April 10. doi: 10.1098/rspb.2007.0313.

PMCID: PMC2211512
Copyright © 2007 The Royal Society
Selecting for fast and slow maturing worms

"The majority of drugs applied against nematodes tend to have a stronger effect on adult mortality than on the juvenile, developing stage (Skorping & Read 1998). It has been suggested that such drugs could give a fitness advantage to worms spending a longer time in the juvenile phase and reducing their reproductive phase (Skorping & Read 1998). However, if worms take a longer time to mature, comparative studies suggest that they will grow larger and more fecund, and are also likely to be more virulent. On the other hand, the main purpose of the drugs is to reduce worm burden, and since fecundity in nematodes tends to be density dependent, the evolutionary effects of drug application may potentially be quite complex."

Link of publication

http://ukpmc.ac.uk/articlerender.cgi?artid=1557269