The **Cloverleaf Weevil** (*Hypera punctata*) is a significant pest of legumes, particularly clover and alfalfa (*Medicago sativa*). It is native to Europe but is now widespread in North America, where it causes substantial feeding damage to hay and forage crops. While both the adults and larvae feed, the **larval stage** is the most damaging, skeletonizing the foliage of the host plants, especially during the early spring growth period.
Taxonomy and Classification
The Cloverleaf Weevil belongs to the family Curculionidae (snout beetles or weevils) in the order Coleoptera. It undergoes complete metamorphosis. It is closely related to the highly destructive Alfalfa Weevil (*Hypera postica*), but the Cloverleaf Weevil is generally less damaging due to its behavior and the strong natural control provided by a specific fungal pathogen.
Physical Description
Adult Cloverleaf Weevils are large, robust weevils, about 8–10 millimeters long. They are a grayish-brown color, mottled with darker spots and scales, and possess a stout, curved snout. They are nocturnal and rarely seen during the day.
The **larva** is the most commonly observed and damaging stage. It is pale green with a distinct, broad, white or cream-colored stripe running down the center of its back. It is legless and can grow up to $1/2$ inch long. When disturbed, the larva often curls into a C-shape, much like a grub. A key feature distinguishing it from the Alfalfa Weevil larva is the larger size and the single, broad white stripe (Alfalfa Weevil larvae have two narrow stripes).
Distribution and Habitat
The Cloverleaf Weevil is found throughout the major clover and alfalfa growing regions of the United States and Canada. Its habitat is primarily legume fields, pastures, and hay meadows. The larval stage is active on the foliage, while the adults and eggs are found near the base of the plants or in soil debris.
Behavior and Life Cycle
The Cloverleaf Weevil typically has only one generation per year. Adults emerge in the summer and fall, feeding on foliage and laying eggs in clusters inside the hollow stems of the host plant. The larvae hatch in the late fall or early spring, and the newly emerged larvae overwinter within the base of the plants.
The larvae begin active feeding in early spring, often causing significant damage to the first cutting of alfalfa or clover. The mature larvae pupate in a loose, silken, net-like cocoon attached to the plant foliage or debris. The adults that emerge in summer are long-lived and overwinter before the next generation.
Feeding and Damage
Larval feeding is the primary source of economic damage. The larvae consume the terminal buds and leaves, chewing large holes or **skeletonizing** the foliage (eating the soft tissue between the veins). This feeding reduces the quality and quantity of the first hay cutting. In severe infestations, the field may appear frosted or silver due to the extensive damage.
However, control measures are often unnecessary because of an effective **natural control**: the fungus *Entomophthora phytonomi*. This fungus often decimates the weevil population, particularly in late spring, causing the larvae to cling to the plant stem and die, mummified in a characteristic position.
Management and Prevention
Because the fungal pathogen *Entomophthora* usually controls the population before economic injury levels are reached, **chemical control is rarely recommended** for the Cloverleaf Weevil. Management focuses on cultural practices:
- Monitoring: Regular scouting is important to distinguish the Cloverleaf Weevil from the more destructive Alfalfa Weevil.
- Harvest Timing: If populations are high, harvesting the first cutting early can remove the larvae from the field before they mature, which is often sufficient control.
- Preservation of Fungus: Avoiding the use of broad-spectrum insecticides helps preserve the natural fungal pathogen, which is the most reliable long-term control.
Conservation and Research
The Cloverleaf Weevil is a manageable pest. Research primarily focuses on the ecology and spread of the naturally occurring *Entomophthora* fungus to understand how this pathogen can be maximized as a primary biological control agent for *Hypera* species, including the more aggressive Alfalfa Weevil.