&middotDrought damage - needles gradually turn yellowish-green and then light brown. This starts at the top of the tree and progresses downward and from the outside in. &middotAnimal injury - dog urine can cause some browning and dropping of lower branches on arborvitae and junipers.
There are many different brands of cat flea collars. Generally, flea collars work by either emitting a toxic gas to the local area (head/neck of the pet) or by exuding chemicals that are absorbed into the animal's skin. Some flea collars have an Insect Growth Regulator (IGR), to prevent development of cat fleas, eggs and larvae.
The fleas on your dog will not bite the cat, but the cat may be a host for a while, until the flea finds a canine and will feed on his blood. The canine fleas are very rare. However, the fleas that are found on cats may be transmitted to dogs, as these fleas have adapted so that they can feed on canine blood as well.