Help!! Plant killing insects.?

Can someone help me identify these little insects that i believe are killing my plants in the backgarden. They are very small and their are bunches of them attatched to the branches next to the leaves. They are lilac in colour with a little white on them too. have tried to soak the plant in water to blast them... show more Can someone help me identify these little insects that i believe are killing my plants in the backgarden. They are very small and their are bunches of them attatched to the branches next to the leaves.

They are lilac in colour with a little white on them too. have tried to soak the plant in water to blast them away but they have simply returned.

Any help on how to get rid of them or indeed should i?

Thanks
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