need some pix .... but i have to say.. a lot of us gave up on this problem plant a long time ago ... you ought to consider such ... if they keep dying.. why do you keep replanting the same thing??? this might be indicative of what happens.. when you plant too many of the same thing.. some little problem multiplies itself in to a nightmare ... i doubt the ants are the primary cause ... unless they are not ants ... ken Here is a link that might be useful: how to post pix

Nothing really "eats" boxwood :-) They can get some - not many - insect issues but these all tend to be sucking type insects. But if the infestation is large enough, it can cause leaf drop. I'm not absolutely sure what the issue is. The webbing is somewhat evocative of spider mites however I don't see any obvious sign of mite damage like stippling and discoloration.....the webbing could just be that of regular spiders and the basal dieback the result of the shading of the lower foliage. Or perhaps some chemical damage....boxwoods are sensitive to road salt. Regardless, it is not anything that will necessarily remain present in the soil or a serious insect pest that would infest any replacements. Just hosing down the plants periodically will discourage any mites and avoid using deicing salt in the vicinity.

in the intervening years.. have the arbs ended up in full shade ??? that might be one explanation for the thinning.. and overall decline ... and once they decline ... lose vigor ... then other things might attack .. sooo ... solving the secondary problem.. might not return vigor ... also ... if the shade trees happen to be highly aggressive super competitors .. like maple... they might not be getting the water they are used to ... especially if there has been severe drought.. in any of the last few years ... it is not uncommon ... for a conifer ... to look bad after winter ... but its not necessarily winter that did it ... the insult or problem could have occurred anytime in the last year.. thats why i mention drought ... its a 'tree time' issue ... things just dont happen this fast with conifers .... i dont do boxwood ... because of all the inherent issues with them ... sometimes its easier to divest.. rather than invest in working with a problem plant ... if it were me.. i would cut out all the dead stuff .. see what happens this year.. and if it lacks vigor.. be done with it in fall ... in the alternative.. after cutting out all the dead .. if it was ugly as sin.. i might just do the removal now ... lifes too short to screw around with a boring old green plant that doesnt flower.. and needs to be sheared all the time.. you can do so much better.. imo ... ken

fert is usually not a response to problems.. or perceived problems in the garden ... are these box potted??? .... the clay pot colored blob in the first pic seems to indicate such ... if so ... potting media is a water management system ... and when it gets old ... it starts failing at water management ... and your pots can get swampy ... and as gal notes... thats not good ... she goes on to say is might be a fert issue in pots ... but fert isnt going to fix a drainage problem ... if you want us to go much further.. favor us with a pic of the plant ... and maybe your location might matter ... especially in regard to your leaf tips browning ... ken