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White grubs, commonly known as the larvae of May beetles, are a group of insects belonging to the genus Phyllophaga. With over 100 different species, Phyllophaga larvae, along with other scarab beetles, are often referred to as white grubs. These insects can cause significant damage to plants, grass, and crops, making it essential to understand their characteristics and implement effective management strategies. This article provides an overview of Phyllophaga spp., including their distribution, description, life cycle, and management techniques.
Phyllophaga spp. and related insects can be found throughout the United States and Canada. However, the distribution of individual species tends to be more localized. May beetles, the adult form of white grubs, are typically 12 to 25 mm long and exhibit various colors ranging from yellow to dark reddish- brown or black. Some species, like the green June beetle, have a more vibrant coloration. On the other hand, the larvae, which are the white grubs, measure between 20 and 45 mm in length. They have a distinctive C-shaped body, a brown head, and three pairs of legs. Underneath the last abdominal segment, two parallel rows of spines can be observed, distinguishing them from similar-looking larvae.
The life cycle of Phyllophaga spp. can vary, with some species completing their growth in one year and others requiring up to four years. The most common life cycle for these beetles spans three years. Adult beetles mate in the evening and females return to the ground at dawn to deposit 15 to 20 eggs, typically 1 to 8 inches deep in the soil. Since the adults are atracted to trees for feeding, they tend to lay most of their eggs in the higher portions of sod near wooded areas. Approximately three weeks later, the eggs hatch into young larvae, which feed on roots and decaying vegetation throughout the summer.
In autumn, the larvae migrate deeper into the soil and remain inactive until the following spring. The most significant damage occurs as the larvae move near the soil surface to feed on plant roots. In late spring, the fully grown grubs create oval earthen cells and pupate. A few weeks later, the adult beetles emerge from the pupal stage, but they remain in the soil. They overwinter and emerge the following year in May or June to feed, mate, and lay eggs.
Managing white grubs is crucial to minimize their impact on crops, plants, and grass. While these pests can be problematic every year, the most severe damage occurs in regular three-year cycles. Here are some management strategies that can be employed:
Crop Selection and Rotation
Plant deep-rooted legumes, such as alfalfa or clovers, during years of heavy May beetle infestation.
Avoid planting corn or potatoes in fields that were previously under sod or grass, following heavy flights of May beetles.
Keep fields free of grass and weed growth to reduce the number of beetle eggs laid.
Plowing
Late spring or early autumn plowing can be effective in destroying many larvae, pupae, and adults in the soil. Plowing exposes the insects to natural predators like birds and skunks. Plowing should be done before the grubs migrate below the plow depth.
Crop Management Practices
No-tillage or reduced tillage crop management should be avoided as it encourages grub populations. Instead, promote cultural practices that discourage grub infestation.
Several natural enemies play a role in controlling white grub populations. These include parasitic wasps and flies, such as Tiphia and Myzinum species (Hymenoptera: Tiphiidae), Pelecinus polyturator wasps (Hymenoptera: Pelecinidae), and the fly Pyrgota undata (Diptera: Pyrgotidae).
Cordyceps fungus is another natural enemy that infects the grubs.
Bacillus popilliae Dutky and B. lentimorbus Dutky are bacterial spores that can be introduced into the soil
to reduce white grub populations. These commercially available products help control the pests.
By implementing a combination of these management strategies, it is possible to reduce white grub populations and minimize their impact on crops and plants.
White grubs, specifically Phyllophaga spp., can pose a significant threat to agricultural crops and plants. Understanding their life cycle, distribution, and characteristics is crucial in developing effective management strategies. By employing techniques such as crop selection and rotation, plowing, promoting natural enemies, and bacterial inoculation, it is possible to mitigate the damage caused by white grubs. Integrated pest management practices that incorporate these strategies can help maintain healthy vegetation and reduce economic losses associated with white grub infestation.