North American Fruit Explorers mailing list at ibiblio

["Donna &/or Kieran" <holycow@cookeville.com>]

Scott,   Do you have many wasps around your place?  Would you consider 
hanging some birdhouses or something like birdhouses, gourds, etc, in or 
around your persimmon trees?   I've been trying to think of what could get 
inside the wrapped leaves, and I wonder if wasps would go for them.  Wasps 
are good to have around anyway as they are carnivores.  We have a lot of 
birdhouses up and some of them get used by wasps.  I like that better than 
in the shed or somewhere else I might get into them.  I'll bet if you made 
some birdhouses with the holes too small you'd get wasps, or hang up 3 close 
within 12 feet or so of each other.   You may get a couple with birds in 
them, the other with wasps.  The birds may very well figure out how to get 
the psylla too.    Donna

http://www.tfrec.wsu.edu/IPMnews/IPM080198.html
Here's an interesting article on pear psylla and natural enemies.  Here are 
a few quotes from this article:

Many insects have been found to prey upon pear psylla in the Northwest. 
Among the more effective generalist predators are a number of predatory 
bugs, including Deraeocoris, campylomma and several anthocorid species, as 
well as lacewing larvae and coccinellid (ladybird) beetles. Earwigs have 
been shown to be a good psylla predator; with their nocturnal habits they 
often escape detection. Even vespid wasps (yellow jackets) can feed on and 
reduce psylla populations (although they can be a problem come harvest 
time!). There are a few species of encyrtid wasps that parasitize pear 
psylla. One species, Trechnites insidiosus, has provided up to 70% 
parasitism in unsprayed orchards. Natural enemies can readily colonize pear 
orchards in many locations and provide adequate pear psylla control. 
Unsprayed orchards typically do not develop damaging psylla populations.

After psylla became resistant in commerical orchards and populations 
exploded:
The use of insecticides (Guthion, diazinon, Carzol and pyrethroids) found to 
be hardest on the psylla natural enemies was eliminated or greatly reduced. 
Thiodan and Imidan, both somewhat less toxic to the true bug predators, were 
included in the program, as well as some other less disruptive materials. 
Many growers had to apply high-volume sprays of a detergent to their trees 
in the later summer to remove honeydew from the leaves and fruit. Within two 
seasons most growers had established effective biological control of psylla, 
resulting in not only cleaner crops but also less expense.

It is important for successful psylla biocontrol that the complex of natural 
enemies begin their work early in the season and continue through the summer 
into the fall. Predators that overwinter nearby as mobile adults can be 
needed to get biocontrol underway by bloom. Psylla reproduce rapidly and if 
the predators and parasites arrive too late they can fail to keep the psylla 
below damaging levels. One early season spray that kills natural enemies can 
stop effective biological control for the season.