Question

An aphid has two modes of reproduction; sexual, when food is sufficient and .............. when there is scarcity of food and uncrowded.
A. Budding
B. Fragmentation
C. Parthenogenesis
D. Gemmules

Answer 1

Hint: Aphids are small sap-sucking insects that belong to the family Aphidoidea. They feed on small stems, branches by piercing the stems and sucking the nutrient-rich sap from the plant. The common names include blackfly and greenfly.

Complete answer:

Budding is a method of asexual reproduction in which a new individual is developed from an outgrowth or a bud due to cell division at a particular site in the parental cell. Since the mode of reproduction is asexual, the new individual is identical to the parent cell. An Example of organisms budding in yeast. A small bulb-like projection coming out from the yeast is observed.
-Fragmentation is another type of asexual production in which an organism is split into fragments. Each of the split fragments develops into a fully mature organism that is genetically and morphologically identical to the parent. Fragmentation is observed in various types of algae.
-Parthenogenesis is a mode of reproduction in which an egg cell is fertilized without being fused with a sperm cell. It is regarded as a form of asexual reproduction since a zygote is formed without the union of male and female gametes. This type of reproduction is seen in many plants and invertebrates such as the aphids, stick insects, some species of ants, etc.
-Gemmules are small buds found in the sponges that take part in sexual reproduction. These structures are resistant to dehydration, freezing, and can survive without oxygen. 

Hence, the correct option is (C) Parthenogenesis

Note: Aphids reproduce by parthenogenesis when there is a scarcity of food and is uncrowded. Aphids produced have genetically identical winged and non-winged female progeny. Some of the aphids alternate their life cycles between genetic control and environmental control to produce winged and wingless forms.