Huh, have to say this week's concept is particularly intriguing. I wasn't able to come up with ideas for the last two weeks, but think this time I can settle on a fun team for the concept relatively quickly. (yay, more guardian signs rep!)
So, what's to do on Renbow Island? The Wireless Tower comes to mind, and then there's the somewhat large forested area to the west. There's also Rasp Cavern, which doesn't have much outside it (except for being the site of a certain minor event in the wireless missions...), and of course, it's an island, which means plenty of water.
To "bug" someone can refer to many things - annoyance, trying to listen in on them, or very literally, using an actual bug. There's some material to work with here. Our hypothetical bug specialist will be someone hired to perform casual espionage over in Renbow Island, to inform Rangers of any suspicious activity if they're on a different island. As a result, their team isn't necessarily the best suited to direct battle, but it can annoy the foe just enough to throw them off their groove and find an escape opportunity.
While I definitely agree with CTNC's idea of field moves dictating a Pokemon's role given the context of Ranger, I want to expand on that a bit further, by including moves that align with the specific field move (to some degree). All such moves have been
italicized.

First up, Sunkern. Field move: Cut x1
Ability: Chlorophyll
-
Cut
-
Razor Leaf
- Grasswhistle
- Ingrain
At a small height of 0.3m, Sunkern's very easy to miss. Heck, you need a field move to even engage its evolution in battle on another of Oblivia's islands, so it's reasonable to assume Sunkern could just plant itself in the soil and listen in on any conversations as a sprouting bud.
With Grasswhistle, it can put targets to sleep, and ingrain itself as a form of camouflage. But if all else fails, it can cut surprisingly sharp with its Razor Leaves for a quick getaway.

Second up, Spinarak. Field move: Slam x1
Ability: Insomnia
-
Body Slam
- Spider Web
- Toxic Spikes
- Bug Bite
Spinarak may be a bit taller, but its green color, ability to spin webs and hide among trees is particularly invaluable given how much greenery is found on Renbow Island.
Sure, 8.5 kg isn't much of a body to slam with, but Spinarak doesn't learn any other relevant moves to slam with. Spider Web acts as the quintessential web to trap others with, while Toxic Spikes is more helpful for ambushing a particular target that arrives later. Lastly, Bug Bite prevents foes from staying alert by munching on their berries before they can.

Third up, Zubat. Field move: Cut x1
Ability: Inner Focus
-
Air Cutter
- Supersonic
- Leech Life
- Hypnosis
Given Rasp Cavern being as large as it is, it only makes sense to have someone perfectly suited to navigating it. Who better to blend in with the hordes of Zubat commonly found in caves and bug unsuspecting passerby?
Air Cutter lets Zubat chip rock formations, which sculpt the perfect area to bounce sound off via Supersonic. With Leech Life, Zubat gets to stay healthy (as healthy as 20 power gets...), and given its association with the move for so long, feels like a more flavorful pick. While Confuse Ray (and Giga Drain) would technically be better choices than Supersonic and Leech Life, this Zubat aims to blend in as far as possible - those special moves might alert targets. Lastly, Hypnosis lets try putting a pursuer to sleep before escaping.

Fourth up, Igglybuff. Field move: Crush x1
Ability: Cute Charm
- Bounce
-
Mega Punch
- Icy Wind
- Perish Song
Wait, how is this here? Well, Oblivia's events don't take place entirely on the ground, the biggest offender being that one tiny Sky Fortress that blew up Dolce Island. While Staraptor might seem like a much better aerial observer, it's also the Pokemon of choice for rangers - so any evil teams seeing a Staraptor would know to fight or flee. However, a small pink puffball like Igglybuff could easily camouflage itself among the clouds by filling up with air and floating high enough!
With Bounce, Igglybuff can float into the air and slowly unleash cold wind to slow down targets. If it needs to fight, a solid Mega Punch gets the job done, but if it's got to bug something instead, it settles for the ultimate move in its arsenal - Perish Song, that will no doubt cause mass confusion and annoyance, bugging all those that hear it.

Fifth up, Krabby. Field move: Cut: x1
Ability: Shell Armor
- Bubblebeam
- Fury Cutter
- Mud Shot
- Dive
Given that we're on an island, it helps to have someone who can bug the beaches and/or shallows, to see who comes aboard. Since Krabby tend to blow bubbles on the beach (courtesy of PMD Explorers), a casual observer might not see another one lurking nearby. As such, this is why it's not evolved into Kingler.
Krabby uses Bubblebeam as its camouflage, while Mud Shot lets it launch an attack that blends in with the beach's sand, slowing down targets to the point Fury Cutter builds up power. And as always, Dive lets it explore the ocean nearby, to see if any Wailord, ancient stone slabs that summon Ho-oh, or cargo ships happen to be stuck.
Last up, Jolteon. Field move: Electrify x3
Ability: Volt Absorb
- Pin Missile
- Detect
- Last Resort
-
Shock Wave
After the events at the Wireless Tower, it makes sense to have an Electric type that could stand up to Raikou, at least somewhat. Meet Jolteon, who presents as the ace of this team, and has had access to a Bug type move since the first Generation, somehow.
It can detect to avoid detection, and launch pin missiles to bug foes further. Shock Wave lets it always strike a particularly evasive target, and when all else fails, it has its last resort, Last Resort to launch as a powerful physical blow.
