Persons is very rare in normal English speech. Mostly you only come across it in legal or other "official" contexts such as...
The defendant conspired with a person or persons unknown to blow up the House of Lords.
6 persons maximum/Licensed to carry 4 persons (notices on lifts/taxis).
In most normal contexts the plural of person is people. When making a restaurant booking, for example, you'd normally ask for a table for six people - if you said six persons that would suggest you're nervous, unfamiliar with such situations, and foolishly trying to sound "correct" in an inappropriate context. If it was a swanky restaurant they might just say they're fully booked because you sounded gauche.
Individuals is also relatively uncommon in speech, tending again to be restricted to official (particularly, written) contexts. Probably because of this, if you said you saw four individuals somewhere, it might well imply four suspicious-looking characters, since the phrasing is typical of witnesses giving evidence in court, rather than everyday conversation.
Note that individuals carries no connotations of each individual being significantly different to every other. Identical twins wearing similar clothes are still two individuals, if the context permits using the term at all.
There's more on this subject in Person, Persons, People, Peoples, which was asked previously on ELU, but for most purposes I suggest it's enough to note that the standard forms are person/people.
In the first example, the object contains to only one process; immediate removal of pods from harvested plants (even though pods is a multiple). Therefore, is is correct.
In the second example, the object contains more than one process; protection against contact with the disease-carrying mosquitoes and mosquito control. Its more than one, so are is correct.
Best Answer
This refers to a set which contains several kinds of flowers. Ex. "The bouquet was made up of a variety of red flowers." (They're all red and part of one set, but are different from each other in terms of genus, species, cultivar, and so on.)
This refers to multiple sets, each set containing many instances of one kind of flower. Ex. "Several varieties of flowers are available for purchase." (A flower shop offers several different kinds of flowers, and they sell more than one of each.)
This refers to a subset within the set of the whole, as in one kind of flower among all kinds of flower. Ex. "A variety of flower may hold they key to curing cancer." (One particular kind of flower contains compounds that have some effect against cancer, but flowers in general do not have such properties.)
This refers to several distinct subsets within the set of the whole. Ex. "Several varieties of flowers bloom all year round." (There are several kinds of flower that blossom throughout the year, but there are also those that do not.)