The "worm" commonly found inside a plum is actually the larva (grub) of the Plum Curculio, a type of weevil.
Understanding the Plum Curculio
These unwelcome guests are the immature stage of a small, brown-black weevil (scientific name: Conotrachelus nenuphar). The adult weevils typically overwinter in leaf litter and ground debris in or near the orchard. As temperatures rise in spring, they emerge, feed on developing fruit, and lay their eggs directly into the young plums.
Once the eggs hatch, the tiny, white, legless grubs begin to feed within the fruit, creating tunnels and causing the plum to prematurely drop from the tree or become unmarketable. These grubs are the “worms” so often encountered in fruit that has not been adequately protected.
Characteristics of Plum Curculio Grubs
- Appearance: White or creamy white with a distinct brown head.
- Legs: They are legless, which differentiates them from other insect larvae that might infest fruit.
- Size: Small, typically reaching about 1/4 inch in length when mature.
- Damage: Their feeding causes internal damage, browning, and often leads to fruit drop.
Plum Curculio Life Cycle
Understanding the life cycle is crucial for effective management of this pest.
| Stage | Description |
|---|---|
| Egg | Laid by the adult weevil just beneath the skin of developing fruit, often in a crescent-shaped cut. |
| Larva | (The "worm") Hatches from the egg and bores into the fruit, feeding on the pulp around the pit for several weeks. These are the white, legless grubs. |
| Pupa | Once mature, the larva exits the fruit (usually after it drops) and burrows into the soil to pupate. |
| Adult | Emerges from the soil later in the season (often late summer to early fall), feeds on some fruit, and then seeks overwintering sites in leaf litter or ground trash to repeat the cycle the following spring. |
Protecting Your Plums
Preventing Plum Curculio infestation is key to enjoying worm-free fruit. Integrated pest management strategies are often recommended for home growers and commercial orchards.
- Sanitation: Regularly remove dropped fruit from around trees, as it may contain developing larvae.
- Weed Control: Keep the area around trees free of weeds and ground trash where adults might overwinter.
- Monitoring: Use visual inspections or trap methods to detect adult weevil activity early in the season.
- Protective Measures: For home growers, options can include fruit bagging for individual fruits or appropriate, timely application of pest control methods if the infestation risk is high. For more detailed guidance on control specific to fruit trees, resources from university extension services, such as those from the University of Illinois Extension or the Mississippi State University Extension, provide valuable information on managing fruit pests.
By understanding the Plum Curculio and its life cycle, growers can take proactive steps to protect their plum harvest from these common pests.
