The boll weevil (Anthonomus grandis) is a small beetle that has become one of the most historically damaging pests in agriculture. Originating in Central America, this insect migrated into the United States in the late 19th century, quickly devastating cotton production across the South. The immense damage it causes stems directly from its highly specific diet, which centers almost exclusively on the reproductive structures of the cotton plant.
Exclusive Focus on Cotton Plants
The cotton plant (Gossypium species) is the primary food source for the boll weevil, providing nourishment for survival and reproduction. The most significant feeding damage occurs on the plant’s fruiting structures: the “squares” (developing flower buds) and the young “bolls” (the fruit containing the fiber and seeds).
Adult weevils use their elongated snouts to puncture these squares and young bolls, consuming the internal plant material and pollen. This feeding causes the damaged squares to turn yellow and often drop from the plant, a process known as shedding. If the weevil attacks a young boll that does not shed, the damaged area can become susceptible to boll rot, severely lowering the quality of the cotton fiber inside.
Adult females also puncture the squares and bolls to create small holes, where they deposit a single egg before sealing the entry point with a protective cap of frass (droppings). This dual-purpose feeding and egg-laying behavior directly targets the plant parts intended to produce the cotton crop, leading to catastrophic crop losses. A single female can lay up to 200 eggs over her lifetime.
Dietary Differences Between Life Stages
The boll weevil’s diet varies considerably between the mobile adult and the developing larva. Newly emerged adult weevils feed on the reproductive structures, such as squares and bolls, to gain the energy needed for mating and egg production. This feeding can also include other parts of the plant, like terminal buds or leaves, especially when fruiting structures are scarce.
The larval stage is completely dependent on the food source chosen by the mother. Once the egg hatches inside the cotton square or boll, the legless larva (grub) begins to feed immediately on the moist, internal tissues. The larva remains trapped within this protective casing, consuming the contents for one to two weeks before it pupates. Because the larva does not leave its initial feeding site, it consumes the developing pollen, petals, and ovules, effectively destroying the potential for a marketable cotton boll.
Survival on Alternative Host Plants
While cotton is necessary for the boll weevil to reproduce successfully, adult weevils can feed minimally on a selection of other plants for survival. These alternative hosts are primarily members of the Malvaceae family, which is the same plant family as cotton. Plants such as okra and certain species of wild hibiscus have been identified as temporary food sources.
The adult weevil may use these plants for maintenance feeding, especially during times when cotton is not fruiting, such as before the growing season or during the overwintering period. Studies have shown that the longevity of adult weevils is significantly increased when they have access to the flowers of plants like hibiscus.
These alternative hosts generally only provide enough nourishment for the adult weevils to survive until they can locate a cotton plant. They typically do not support a new breeding population, as the offspring require the specific internal environment of the cotton square or boll for successful development.