Killing the host...

[Externet]

Somewhere I read once that parasites and illness causing organisms had evolved to <not kill the hosts they infected>  as to keep the nourishment and reproduction grounds for looong times.

My peach tree is dropping immature fruit with signs of being drilled by some insect and a worm inside. 

Could the <not killing the host> be applied here or the fruit rotting on the floor is the real benefit of the worm strategy ?   Obviously, the fruit (or the tree?) senses being affected and somehow the peach is let go.  How does it work ?  Now that I think; the tree is not destroyed for next year cycle.  Just the fruit is.  Strategy ?

 

[CharonY]

4 hours ago, Externet said:

Somewhere I read once that parasites and illness causing organisms had evolved to <not kill the hosts they infected>  as to keep the nourishment and reproduction grounds for looong times.

That is not always the case- it is more a rough tendency, which is not always correct. In quite a few parasites, the reproductive fate of a parasite is not coupled to their hosts, so they do not benefit from the host being alive longer (or conversely, there is no disadvantage for them to kill them- as long as they do not run out of hosts). In fact, in some cases the death of the host is a necessary part of their life cycle. Some fungi, for example, feed on their insect host until they are pretty much spent, then cause them seek a high point for maximum spore dispersal. Certain horsehair worms infect their hosts brain and cause them to drown, so that the worm can get into water and lay eggs. Some parasites have to change hosts during their lifecycle and either cost their first to die (or compel them to get eaten) so that they can get to their second one. 

Sometimes the opposite happens. Plasmodium falciparum, which causes malaria, is harmless to mosquitos, but an be quite deadly in their final host.