"Feeding your larvae 'bad' leaves may make them sick and who wants unhealthy caterpillars? Remember, poor food quality often = problems with completing a healthy life-cycle…"http://www.mymonarchguide.com/2007/08/m ... blems.html
Milkweed leaf 'problems'
Aphids can transmit/cause diseases to be transplanted to the plant and the other insects that eat it. This was an interesting article about how ants protect aphids from a fungal infection:http://rsbl.royalsocietypublishing.org/ ... 5.full.pdf
"Ants defend aphids against lethal disease"http://ipm.illinois.edu/diseases/rpds/926.pdf
Page 2, "Disease Cycle" next to the last paragraph
"CMV is usually introduced into cultivated vine crop fields and gardens by more than 60 species of aphids (especially the green-peach aphid, Myzus persicae) after they pick up the virus by feeding on reservoirhosts for a few seconds to a minute (non-persistent transmission)."
This is very interesting:http://www.ipm.ucdavis.edu/PMG/r280101411.html
In open field crop production, silver reflective mulch has been shown to repel aphids and whiteflies, thus reducing their numbers in and around plant canopies. In addition, virus transmission by these insects was greatly reduced. For best results, apply mulches at the time of planting or transplanting the crop. Apart from reducing aphid and virus incidence, silver reflective mulch increased cut flower production and reduced the crop requirement for irrigation water and fertilizer. This method is acceptable for organic production."