Anthonie Heinsius wrote to Leeuwenhoek about Robert Boyle's reaction to the letter about cochineal

August 21, 1685

We know about this letter because Leeuwenhoek quoted from and responded to it in Letter 105 [60] of 28 November 1687. Heinsius initiated this sequence of letters in July by passing along to Leeuwenhoek a request from Robert Boyle that Leeuwenhoek examine cochineal. Leeuwenhoek did so and reported his observations in early August, after which Heinsius showed the letter to Boyle. In late August, Heinsius reported back on Boyle's response.

To this, the abovementioned Mr. Heinsius replies to me from Westminster on the 21st/31st August.

I have communicated to Mr. Boyle the contents of the missive which you sent me, about which His Honour was very satisfied. He requested me to thank you for the trouble you have taken, etc:

Your argument concerning the invariably similar littele animals in the Male seeds, etc:.

As regards the Cochineal, he says that he understood from a Governor of Jamaica that the same originates in the fruit of a Figtree, which, on rotting or putrefying, produce worms, or cocoons, which change into Flies and these settle and hold themselves on very tight to the tree; a fire is then lit under the tree, and the smoke causes them all to fall down, and after they are caught the head and the foremost part, together with the wings are removed and the rest is kept, so that the Cochineal is really the hindmost part or the tail of the fly. And furthermore, he has approved of the observation which You yourself made concerning the matter, and he is of the opinion that what You have seen are, in fact, eggs, just as we find such eggs in the Abdomens of the Silk-worms' moths.

The footnote in Collected Letters, vol. 7, p. 137 notes that Heinsius was "at Westminster as a member of a deputation from the States General, to solve the disputes that had arisen between the English and the Dutch East India Company in the matter of Bantam."