Effectively defending yourself against Wyverns as a low level Apprentice isn't too difficult in comparison to the other classes, considering almost all your towers are projectile towers and the Apprentice has decent range. Let's look at what an Apprentice has to offer.
Towers
Magic Missile Tower: Using well placed Magic Missile towers is often enough to cover Wyverns on Easy, Medium and even Hard difficulties, depending on the map and your stats. MM towers do not do a specific damage type and thusly enemies cannot be immune to them. Upgrading your Defense Attack Rate is excellent on an Apprentice in general, as it ups your DPS. MM towers have the advantage in that they have a low DU, so you can set them up in key positions without worrying about filling your DU quota too quickly.
Fireball Tower: Fireball towers do really strong splash damage and have a higher base range than MM towers. However, their attack rate is a bit slower, and fire-immune Wyverns will be a problem. Using a single Fireball tower without other coverage will let fire-immune Wyverns through your defenses, however they work excellently in tandem with other towers, doing decent AoE damage.
Lightning Tower: Lightning towers have an advantage in that unlike MM and Fireball towers, they can fire through walls. This lets them get around corners and while their range is different from the other towers in that it is not a cone, but an AoE around the tower itself, you can give them a gigantic effective range, including in height. However, like with the Fireball tower, immunities will be a problem if they're your only source of coverage.
Deadly Striker Tower: While it comes in at a whopping 8 DU, the Deadly Striker is incredibly effective against Wyverns, often one-shotting them. It's rather overkill though for Easy and Medium difficulties, especially on the earlier maps where your DU limit is low. Until you put some substantial points into Defense Attack Rate, the firing rate on the Deadly Strikers may be too low for them to effectively take out Wyverns, so they do require some investment. However, they're very effective and pretty much essential for some setups in Insane and Nightmare mode. At your current level, you're probably better off investing in MM towers instead. Like the Lightning Tower, they can fire through architecture and they can end up having a very long effective range.
Placement Tips and Being Prepared
While knowing your own tower strengths is important, the most important thing to learn when defending against Wyverns is effective tower placement. You can have a great setup with multiple tower types, but if it's facing the wrong direction, it's not going to help you at all. When facing Wyverns on a new map that you haven't played, make sure you pay attention to where they are coming from. These locations will remain the same each time you play the map. On some maps, you'll have Wyverns coming from only 2 locations at first, then more later on. Try to remember which waves they show up where. In addition, be aware of your own towers' effective range limits so you know that you're getting decent coverage.
This is Magus Quarters. The blue X's are where the Wyverns come from the first time they show up. The red X's are where I usually set up a tower (facing at an angle southwards, towards the marked doors) to take care of them because they fly directly over the lava towards the crystal. Learn these key locations for every map you play.
In addition, you'll get a large popup on your screen telling you to "Beware the Wyverns!" during the setup for the wave prior to their first appearance. Pay attention to this so you know when you'll have to prepare for them. If you're playing a map you've played before and you know they show up on Wave 4, make sure you have a tower setup to take care of them by Wave 4. On higher difficulties, you may want to set up towers beforehand and level them up so they're strong enough to handle the influx.
Helping Hands
While Dungeon Defenders can obviously be played solo, I have the most fun and the most challenge playing with friends. The maps scale to how many people there are, so while you will end up with more Wyverns when playing with more people, you'll also have more ways to take care of them. Here are some short tips for the other classes:
The Squire's/Countess' Harpoon Turret received a buff in patch 7.20 to improve their target leading and tracking. A single Harpoon turret in the locations I mentioned above in Magus Quarters will also work well. Harpoons can also penetrate enemies, which make them great for large clumps of Wyverns, in addition to the fact that they do physical damages, so you don't have to worry about immunities. Cleverly placed Slice n' Dice towers can also work well, such as on the roof in The Ramparts.
The Huntress'/Ranger's Ethereal Spike Trap will be triggered by enemies in the air, though honestly, there's really better options to use for anti-air defense. In addition, while their Proximity Mine Trap can only be triggered by ground enemies, it will damage flyers when triggered, so these can also be placed close to the crystal as an "oh shi-" measure and detonated manually. It does physical damage, so you don't have to worry about immunity. In addition, some Huntresses/Rangers choose to do DPS-only builds, which make them incredibly effective for taking out Wyverns. Let them know that one has slipped through your towers, or have them stand and help thin the flocks before they even get there.
The Monk's/Initiate's Slow and Electric Auras are also very effective, especially given that the auras can cover a very large area on a character with lots of points in aura size. While Electric Auras will suffer the same immunity issues, you can still use them in tandem with other towers. Slow Auras will slow down the Wyverns, clumping them up for piercing from the Harpoon Turret or splash damage from a Fireball Tower, for example.
Hopefully these tips will help you out! If you need anything clarified let me know in a comment.
