Damage from the Japanese beetle (Popillia japonica) occurs during both the adult and larval stages. Adult beetles feed on the upper surface of leaves, chewing the tissue between the veins and leaving behind a distinctive skeletonized appearance. This lacelike damage is often concentrated at the tops of plants, as adults are gregarious feeders and typically begin feeding at the uppermost foliage before moving downward. Severely damaged leaves turn brown and fall off, which can weaken the plant and reduce its aesthetic and commercial value.

Larvae, or grubs, live just beneath the soil surface and feed on the roots of grasses and various crops. They are most commonly found in well-maintained turf areas such as lawns, parks, and golf courses, and less frequently in pastures. Early signs of grub damage include thinning and yellowing of the grass, followed by wilting and the appearance of irregular brown patches in late summer or early fall. Grub feeding can also damage the roots of agricultural crops such as maize, beans, tomatoes, strawberries, and nursery plants, reducing plant vitality, yield, or even causing plant death. In many cases, secondary damage from birds and mammals digging for the grubs can be more disruptive than the feeding itself, further damaging the sward and soil structure.

The Japanese beetle (Popillia japonica) has a well-defined and seasonally driven life cycle that includes egg, larval, pupal, and adult stages. Females lay their eggs in the soil during the summer, typically from mid-May to mid-July, shortly after mating. Freshly laid eggs are about 1.5 mm long, pearly white, and oblong, but absorb moisture from the soil and become spherical, nearly doubling in size within a week. As they near hatching, the developing embryo becomes visible inside the egg.

The larvae are typical scarab beetle grubs: C-shaped with yellowish-brown heads and strong mandibles. Upon hatching, the grubs are translucent white and about 1.5 mm long. They go through three instars, with the first and second reaching approximately 11 mm and 19 mm, respectively. The mature third-instar grub is about 32 mm long and feeds actively on plant roots during late summer and fall. As temperatures drop, the grubs move deeper into the soil—about 15–20 cm—to overwinter.

In early spring, rising soil temperatures prompt the grubs to return to the upper soil layers (2.5–5.0 cm deep) to resume feeding. After 4–6 weeks of feeding, they stop feeding and transform into pale, shrunken prepupae, and eventually pupate within an earthen cell. The pupae are cream-coloured and resemble adult beetles, gradually turning tan and then the metallic green of maturity. Pupation lasts about two weeks.

Adult beetles, broadly oval and 8–11 mm long, emerge from the soil starting in late spring. They have a dark metallic green head and body with copper-green legs, and females are generally larger than males. After emerging, mating occurs quickly and females begin laying eggs within days. A single female may lay 40–60 eggs during her 30–45 day lifespan. The new larvae begin feeding on fine roots and organic matter shortly after hatching, molting to second and third instars through the summer before descending into the soil once again to overwinter. This annual cycle ensures consistent pest pressure, particularly in areas with extensive turf or susceptible crops.

Preventing Japanese beetle infestations is difficult due to the insect’s mobility and ability to travel from nearby untreated areas. Even if a lawn, garden, or field is carefully managed, adult beetles can fly in from neighbouring properties, parks, or wild areas to feed and lay eggs. This makes it challenging to prevent infestations entirely, especially in regions where Japanese beetles are already well established.

Maintaining healthy turf and plants is one of the best preventative strategies. Proper irrigation, fertilization, mowing, and soil aeration can promote strong root systems that are better able to tolerate larval feeding. Avoiding overwatering during peak egg-laying periods (mid-June to August) can reduce the survival of eggs and newly hatched grubs, as the beetles prefer moist soil for laying eggs. Additionally, choosing plant varieties that are less attractive to adult beetles can help reduce feeding pressure in landscapes.

Regular monitoring for adult beetles during their flight period is important for early detection. If beetles are observed feeding, physical removal in small gardens or the use of barriers and traps (used cautiously) may help reduce numbers. However, for long-term management, especially in high-pressure areas, prevention must be combined with targeted treatments and, ideally, community-level cooperation to limit the beetle’s spread and population buildup.

Larvanem is a biological control product that contains the entomopathogenic nematode Heterorhabditis bacteriophora, which is highly effective against soil-dwelling larvae of the Japanese beetle (Popillia japonica). These beneficial nematodes actively seek out and infect the beetle grubs in the soil, entering through natural openings and releasing symbiotic bacteria that kill the host within 24–72 hours. The nematodes then reproduce inside the grub and search for new hosts, continuing the control process.

For effective suppression, Larvanem should be applied annually, with the ideal timing being late summer to early fall—when most of the grubs are still in the early stages and feeding near the soil surface. This is when the nematodes are most likely to find and infect the larvae. Applications can also be made in spring, before the grubs pupate, but effectiveness is generally higher when targeting younger, actively feeding larvae.

Successful use of Larvanem depends on soil conditions. Moist soil, moderate temperatures, and thorough irrigation before and after application help ensure that the nematodes survive and move effectively through the soil. Because the Japanese beetle is highly mobile and often reinfests from untreated areas, Larvanem is most effective when used as part of an integrated pest management strategy that includes consistent annual applications and broader community involvement.