Research point - Natural sciences.

I started with some online research and found this video from the Natural History Museum then went on a study visit, primarily focussing on botanical illustration.
I started at the Shirley Sherwood Gallery at Kew Gardens which, surprisingly was the first gallery in the world dedicated to botanical art. The exhibition dedicated to seeds, pods and autumn fruits was full of illustrative art. Almost all the pictures were watercolours on a white background. They were representative images, often photorealistic which relied on composition to differentiate different practitioners.
There was an installation, Life in Death by Rebecca Louise Law which was an immersive experience,  dried flowers and plants suspended from the ceiling with wires. (I have also seen The City Garden  in the City Centre in London) Maybe this isn't strictly illustration but it invites the viewer to really engage with the plants. Photography is everywhere and it is easy to become blind to the images. Alternative methods to capture the viewer's imagination helps to convey a message, Law's work is about natural change and beauty in decay and visitors to the gallery were taking time to look at the installation.
Like the graphic quality of Monika de Vries Gohike's Papaya Carica papaya and Rosie Sanders Dandelion: 'Two o'clock' which managed to be dynamic and show movement despite being a plant portrait. Actually I like lots of her flower paintings which are bold and striking, (many flower paintings seem weak and apologetic)
The adjacent Marianne North Gallery  has an overwhelming display of 833 oil paintings. Miss North painted what she saw, so you see the plants in their natural environment, this is botanical reportage.
From Kew I went to the Natural History Museum to see the Images of Nature exhibition promoted by the video I started with.  This is an attempt to cover the history of scientific illustration from early drawings and paintings through to modern investigations using CT and microscopy to investigate specimens. Drawing is a useful tool employed by scientists to understand what they are looking at. Arthur Harry Church was a botanist who made marvellous detailed illustrations of plants that he had dissected. Although they are a scientific tool they still sing with colour more than 100 years after they were painted. Church said "until one has drawn it it is impossible to understand".
There was a composite photograph of a fly by Giles Revell (interview here) which caught my eye. The image is created by merging scans using an electron microscope. Revell is a primarily a photographer who uses digital manipulation to create graphic illustrations of nature such as these abstract colour charts of flowers from the Royal Horticultural Society at Wisley. His work hovers  inventively between photography and computer graphics. There was an exhibition in 2004. Traditional photography is a 2 dimensional exercise which relies upon proper placement and lighting of the subject Revell's manipulations make the images both clearer and more striking, rendering insects, which are often overlooked, more interesting subjects. This is a powerful position to be in as he is capable of modifications which would not be true to the reality of his subjects. He has a choice whether to be purely artistic or illustrative. He is also taking advantage of improved scanning and printing techniques to massively enlarge his subjects.
Mark Ines Russell is an entomologist who has done a series of paintings of weevils looking down a microscope to gain information for a large picture which really brings the insect to life. Again he is a scientist who is using illustration to further his knowledge and to impart information to others, and he is enlarging his subjects using high quality microscopic images.
Elizabeth Butterworth  is an artist who has studied macaws and has an intimate knowledge of them which informs her detailed hyper-realistic paintings. I don't think that she is using new technologies but I note her work here because it is so impressive ( and I'm not generally a fan of hyper-realism).
So scientific illustrators tend to have a detailed knowledge of their subject and are often using illustration to aid their scientific studies or impart information to others. Traditional image making is not necessarily as rooted in fact and is often used to excite or attract the viewer rather than to educate them.