Berachah after eating a blueberry

Hi,

One only recites a blessing after eating if one consumed an amount equal to an olive in volume. However, there is room to argue that one should recite a blessing after eating an entire fruit, even if it is smaller than an olive, such as a blueberry. Therefore, it is best to avoid eating an entire fruit which is smaller than an olive; one should either eat more such fruits in order to exceed an olive's volume, or one should not eat the entire fruit. In practice, though, one who ate such a fruit and did not exceed an olive's volume does not recite a blessing afterward.

(Rav Moshe Feinstein, Igrot Moshe Orach Chaim 1:78)

Have a great day,
Mordechai