The aperture controls the amount of light produced by the flash.
The shutter speed controls the amount of light produced by the ambient light.

So I am always going to get better reception if I couple the antennae on my remotes by pointing my receivers and transmitter straight up.

short distance = power & speed

does not address travel flash setups

when stopping action is not the goal, and a really high shutter speed is not required, then FP Sync can be very useful. In fact, Auto FP is excellent for shooting portraits in bright daylight. Then, you can use a shutter speed well above the normal sync of 1/250th coupled with a wide aperture to blur the background which greatly helps isolate the subject. I typically use camera A mode, ISO 100, FP Sync, f/ 2.8 and 1/1000th in bright shade, and I get a flash range of about 10-15 feet. If I am in really bright light, like on the beach, the shutter has to be around 1/1600th, and this reduces the range to about 8-10 feet which is still reasonable for portraits.

If a greater distance than 10 feet is needed in bright daylight, there is no choice except to use regular flash sync and accept the requisite smaller aperture. This happens frequently when shooting a party outdoors, where I typically shoot in camera S mode, regular flash sync, ISO 100, 1/250th, and f/7, and I get acceptable fill out to 20 to 30 feet or so.

8:21
Nikon Creative Lighting System Tutorial
by Lilkiwiguy87
153,631 views

So the camera shutter speed is not very important if the flash is the main light.
Now, if you are going to try to balance the flash with some ambient light, then the shutter speed in the camera will be important to freeze whatever is being lit by ambient light (background, other people, etc.)

Firstly, we can set shutter speed and flash duration speed separately?
Flash duration is dependent on the flash output power. You don't control it directly (unless you are in manual flash mode), but it is independent from the camera shutter speed.
When there isn't much ambient light and aperture is set to very small, flash duration speed will freeze the moving object.
Basically correct.
When there is strong ambient light, shutter speed freeze the object.
Basically correct. In strong ambient light, your flash acts as "fill light", so motion freeze must be done by camera shutter speed.
When handheld your camera, shutter speed minimise handshake.
The general rule-of-thumb is that you need at least "1/focal-length" shutter speed to counter hand shake. But be aware that this is 35mm-equivalent focal length, so in your D90 ( it's a DX format camera, 1.5x crop) a 50mm lens will be 75mm-equivalent, so you'll need 1/80 shutter speed.
Some people can handhold slower than that, some need higher, depends on how steady you are.

I'm assuming on an insect you're not that concerned with fill light, and that the flash is going to be your key light. In other words, the flash will be your main source of light in these photos.
As a previous poster said, the flash itself is 1/xxxxx of a second, so it will freeze any motion out there. So, your insect will be frozen in time even if the shutter speed was at 1/30.... provided that there isn't enough ambient light to impact the image.
So.. really all you need to do is make your shutter speed / aperture combination tight enough that it reduces the ambient light such that it no longer impacts the photo.
Not sure if this is the look that you're going for, but if you look at just about any stop-action photos you'll notice that all of the light is coming from the flash(es) making the shutter speed much less critical.
The low sync speed really only becomes an issue when you're trying to balance flash with ambient light.

and you will see the recommended f-stop for your shutter speed. Now, go to aperture preferred and set it to higher number (smaller opening). Say the meter says f8 then set the camera to f16. Ambient light illumination will now be two stops darker. Then, use the flash and it will illuminate the closeup subject at the f16 level.
Here is one I took this morning (speg straight from the camera. The leaves were all evenly illuminated by an overcast sky but, those in the background are darker because they were not flash illuminated.

The flash was a Canon 580 EX II with a 14″ Lumodi Beauty Dish mounted on it about 3′ away from the subject.

recommended: gitzo, manfrotto, induro

I have also had cards fail when the tiny metal connectors became corroded from the humidity in Southwest Florida, USA.

Humidity kills memory cards. And brand new cards have a slightly higher failure rate.