According to Tom Turpin, a Purdue University entomology professor, behavioral studies in insects show that, like humans, insect’s sense of taste includes the ability to detect sweet, salty, acidic and bitter tastes. Of these four, only sweet is acceptable to insects. Unlike humans, inse3cts have no interest in the other three.
The sense of taste in humans is facilitated by taste buds located on the tongue. Most humans have around 10,000 taste buds with each is replaced about every two weeks. As we age, all the taste buds aren't replaced. So as we age our sense of taste dulls. Insects', on the other hand, sense of taste is associated with mouth parts, but they also have cells that function in similar fashion to our taste buds that are located on the antennae, legs and the ovipositor. These insect taste buds can be in the shape of a hair, a peg or a pit.
Caterpillars, for example, have taste censors in their mouths. The insect must take a bite to tell if the item is a suitable food. Many adult insects also take bites to determine whether or not to eat a plant. Honey bees use their proboscis to determine sweetness. Some insects use their feet to determine if something is good to eat. If it is, the insect puts down its proboscis in order to begin feeding. Many butterflies and flies walking on something that is good to eat which prompts what is known among entomologists as the tarsal taste and proboscis extension reflex. In other words, if you are standing on good food, the tongue comes out!
In other cases, when a female butterfly stands on a plant, she can also determine if the plant is a suitable host for her offspring. If so, she deposits an egg on the plant. In the same way, a female parasitic wasp can use her ovipositor to taste if another insect is a good potential host for her young.