Dissecting Insect Swarm:
Insect Swarm is a unique DoT as far as DoTs go. For the most part, spells which have an additional effect, such as reducing the target's ability to hit in the case of Insect Swarm, carry with them a penalty to the damage coefficient. Previously, this was true for Insect Swarm. Up until patch 3.1.0, Insect Swarm had a 76% coefficient. Now it has a 120% coefficient, or 20% per tick. Insect Swarm is also different from most conventional DoTs in that it ticks every two seconds instead of ticking every three seconds. While this is more so useful in PvP as it means that the DoT damage is going to be applied faster, this really does not impact the PvE implications of the spell at all. Currently, the only benefit to the faster ticks in PvE is the faster stacking of Idol of the Lunar Eclipse.
Insect Swarm is an oddity of a talent in some respects. Mostly it is a stand-alone ability, which is not common of a staple ability. Beyond Improved Insect Swarm, which doesn't directly increase the damage of the DoT, there are no other talents which increase Insect Swarm's damage directly. While the talent does benefit from our two global modifiers, Earth and Moon and Master Shapeshifter, it does not have anything akin to Improved Moonfire nor it is attached to Moonfury. For any ability that is to remain a solid tool within any rotation, this is very strange, especially for a DoT. Given that most DoTs do not currently benefit from crit or haste base-line, a vast majority of them rely upon potent damage modifiers within talent trees in order to scale properly. Instead, Insect Swarm relies more so on its higher than average base damage and solid spell power scaling in order to remain strong. Is this working, though? Let's do some math and see.
For the purposes of this test, we'll have to run two different gearing sets. One will be a 'starter' Icecrown Citadel level gearing set which contains a mixture of ICC 10, ToC 25, and a few ICC 25 items to represent where the 'average' or 'casual' raider is most likely at currently. The second will be a 'late' ICC gear set which will be comprised of mostly high end ICC 25 items with a few ICC 10 pieces. All applicable raid buffs and debuffs will be applied which includes: Arcane Intellect, Divine Spirit, Blessing of Kings, Moonkin Aura, Improved Moonkin Aura, Arcane Empowerment, Wrath of Air Totem, Improved Shadowbolt, Mark of the Wild, Heart of the Crusader, Demonic Pact (at 350), Earth and Moon, and Improved Faerie Fire. Using a Fish Feast and Flask of the Frost Wyrm will also be taken into account. The talent spec will be a 'standard' raid-centric PvE build.
'Starter' gear stats:
Intellect: 1150 (1405)
Spirit: 638 (847)
Spell power: 2800 (4076)
Crit: 36% (59%)
Haste: 20% (Raid buffs are baked into calculations)
'Late' gear stats:
Intellect: 1405 (1686)
Spirit: 284 (400)
Spell power: 3200 (4373)
Crit: 41% (65%)
Haste: 28% (Raid buffs are baked into calculations)
First, we'll look at the calculations using the 'starter' gear:
Insect Swarm damage:
(215 + (4076 * 0.2)) * (1.06) * (1.04) * (1.13) * (1.03) = 1,321 per tick. At 7 ticks per cast, the total damage done is approximately 9,252.
Wrath (nonEclipse) damage:
(592 + (4076 * .671)) * 1.1 * 1.06 * 1.04 * (1 + ((.59 * 1.09) * 1)) * 1.13 * 1.03 = 7,715
((1.5 / 1.114) / ((1 + (20 / 100))) = 1.1221
(1 -(1-.59)^3)) = 0.9311
(1 * 0.9311) + (1.1221 * 0.0689) = 1.0084
7715 / 1.0084 = 7,650
Wrath (Eclipse) damage:
(592 + (4076 * .671)) * 1.5 * 1.06 * 1.04 * (1 + ((.59 * 1.09) * 1)) * 1.13 * 1.03 = 10,521
10521 / 1.0084 = 10,433
In this case, it is quite clear that a non-Glyphed Insect Swarm is worth casting over a non-Eclipsed Wrath. While the damage of a non-Glyphed Insect Swarm is less than that of an Eclipsed Wrath, this does not exclusively mean that it is a DPS loss to cast during Eclipse. First, we have to determine if the damage difference between Insect Swarm plus the damage gain to Wrath due to Improved Insect Swarm covers the difference between the two.
Wrath (Eclipse + Improved Insect Swarm) damage:
(592 + (4076 * .671)) * 1.5 * 1.06 * 1.04 * (1 + ((.59 * 1.09) * 1)) * 1.13 * 1.03 *1.03 = 10,836
(10836 - 10521) / 1.0084 = 312
312 + 9252 = 9564
Now we can see that Improved Insect Swarm does not increase the damage of Wrath by enough to cover the difference between the two spells. This means that it is not worth casting Insect Swarm during a Solar Eclipse. As the damage disparity between a Solar and Lunar Eclipse is relatively minor, we can also contrive that it is not worth casting Insect Swarm during a Lunar Eclipse proc either.
Since we already know that it is not worth casting Insect Swarm during an Eclipse proc at lower gearing levels, let us see if Insect Swarm's scaling holds up against a non-Eclipsed Wrath at higher gearing levels.
Insect Swarm damage:
(215 + (4373 * 0.2)) * (1.06) * (1.04) * (1.13) * (1.03) = 1,398 per tick. At 7 ticks per cast, that is a total of 9,786 per cast.
Wrath (non-Eclipse) damage:
(592 + (4373 * .671)) * 1.1 * 1.06 * 1.04 * (1 + ((.65 * 1.09) * 1)) * 1.13 * 1.03 = 8,503
Without the need to go any further, we can already determine that Insect Swarm has a higher DPSC than a non-Eclipsed Wrath even at higher levels of gearing, although the disparity is growing smaller. From these calculations, we can conclude that a non-Glyphed Insect Swarm is still a DPS gain to cast when Eclipse is not currently up. There is, however, a small caveat to this. Insect Swarm cannot proc Eclipse whereas Wrath can. This means that inserting Insect Swarm into the rotation causes a delay in the next Eclipse proc. The DPS disparity between Insect Swarm and a non-Eclipsed Wrath - or Starfire as the calculations should be fairly similar - is not significant enough to overcome the difference within a full rotation if, and only if, you were to proc Eclipse within that cast. Proccing Eclipse is a random factor, though, and not something that can be relied upon. Although it is a very minor gamble in very minor DPS differences, casting Insect Swarm while Eclipse is not up is still a DPS gain.