In holometabolous blood-feeding insects, which life stages are present, and which stage vectors disease?

• A. Egg, larva, pupa, and adult; the adult is the vector.
• B. Egg, nymph, adult; nymph vectors disease.
• C. Egg, larva, pupa; pupa vectors disease.
• D. Egg, larva, pupa, and adult; the larva is the vector.

Answer: (A)

In insects that undergo complete metamorphosis, there are four life stages: egg, larva, pupa, and adult. For blood-feeding groups, only the adult stage bites hosts and can transmit pathogens through the saliva during feeding, while the larval and pupal stages are typically not involved in host contact. The adult female has the specialized mouthparts and host-seeking behavior needed to obtain a blood meal and spread disease, whereas the earlier stages remain hidden, feeding on different substrates or not feeding at all. So the life stages present are egg, larva, pupa, and adult, and the disease is vectored by the adult stage.