Prionus beetle infestations have emerged as a critical concern for North Carolina’s blueberry industry, where sudden dieback, crown deterioration, and widespread root damage have been increasingly observed in commercial fields. With confirmed cases of various Prionus species affecting southern highbush plantings, growers have reported severe losses, including the rapid decline of fully mature bushes and extensive uprooting during machine harvest due to weakened root systems. The cryptic nature of Prionus larvae, feeding unseen within crowns and roots for several years, makes early detection extremely difficult, limiting growers’ ability to intervene before irreversible injury occurs. As infestations have now been documented in multiple counties and adult trap captures indicate high local populations, understanding the distribution, severity, and biology of Prionus species in blueberries has become essential. This 2025 monitoring program aimed to establish a season-long monitoring program for the emerging pest Prionus beetles infesting NC commercially grown blueberries. This monitoring program generated valuable new information on the biology of the adult and immature stages of these longhorned beetles and contributed knowledge of the extent and severity of infestations in the state. Check the program’s preliminary summary published in May 2025 at: 2025 Prionus Beetle Monitoring Program in Blueberries

Six commercial blueberry farms in Pender, Sampson, and Bladen Counties, NC, including three farms with adult Prionus reported and larvae actively feeding on plants (confirmed infestation) and three farms with only adult Prionus reported (no reports of blueberry plants infested with larvae) were included in the monitoring program. Two black panel traps baited with Prionus lures (female sex pheromone) were set to collect males (~1 acre apart). Black panel trap with pheromone lure hung with a garden hook in the ground. Wiper fluid (without coolant) or propylene glycol (50:50 or 40:60 mix with water) were used as trap liquid to collect adult beetles attracted to the lured traps. Trap liquid was replenished weekly, and traps were checked weekly at each location. Traps were serviced and collected from March 26, 2025 (before the start of adult Prionus emergence reported in literature), to September 19, 2025 (until we recorded at least two consecutive weeks with no beetle collections). The number of adult Prionus beetles per trap and farm was recorded weekly. Adults collected were brought back to the Small Fruits and Tobacco IPM Lab in Raleigh, NC, for identification using morphological taxonomic keys.

Effective monitoring of Prionus beetles is vital to identify adult emergence patterns and mating periods to inform blueberry pest management programs. In literature, the larvae of Prionus beetles feed on roots for 3-5 years before pupating in the soil and emerging as adults. Lures consist of the female sex pheromone, attract only adult males, and are strong enough to catch beetles from long distances, which is why one traps per acre are recommended for monitoring purposes.

Traps were set up on March 26, 2025; however, beetles were not collected until April 1, 2025 (Week 1, Table 1). Thus, we identified and collected the first group of adult males emerging from the soil after pupation in early spring. Likewise, we were able to detect the end of Prionus adult emergence during the end of August (Week 23, Table 1), and we continued sampling for two more weeks until accumulating two weeks without adult collections. During the 25-week monitoring program, a total of 5,260 adult Prionus males were collected from the six commercial farms sampled (Table 1). Prionus imbricornis and P. pocularis larvae were confirmed using morphological keys and PCR with adult male DNA.

An average of 19 adult males were collected per two traps, overall locations, and weeks (Table 2). The highest average per two traps observed was during the peak in May collections (89 males per two traps, Table 2). A maximum of 280 beetles per two traps were collected during the same period. This is an indication of the effectiveness of the sex pheromone lure used in the panel traps.

The number of adult Prionus males emerging from the soil and collected in the lured traps in the commercial farms increased rapidly during April, peaked in May and slowly decreased during June. It is important to note that despite finding all these adult beetles in the lured traps within commercial blueberry farms, it doesn’t mean that all adults come from blueberry fields. Since these males are strong fliers, they could have emerged from blueberry fields and/or adjacent forest patches where they also infest hardwood tree species. Prionus males emerge and immediately mate with the females, which are non-flying insects. The females can lay eggs immediately after mating. Thus, the months of peak adult emergence are the same months of mating and egg laying. It is unknown how long the eggs take to hatch, but we have a good estimate thanks to measurements taken during this study and discussed in the larvae monitoring section below. Despite not having any insecticides available for Prionus control, they are under development and, hopefully, will be available in the coming years. The farms with active larval infestations in this program are at higher risk of infestation during this study, and neighboring farms should be prioritized for monitoring and management when these chemical tools become available.

In coordination with the blueberry growers, three wilting and dying plants were uprooted per farm from February 2025 until October 2025 (ongoing). The three farms with confirmed Prionus larvae infestations were sampled monthly, while the other three farms were sampled 1-2 times throughout the year. Uprooted plants were brought back to the Small Fruits and Tobacco IPM Lab in Raleigh, NC, cut open with axes and small saws, and examined to record the number of Prionus larvae feeding on each blueberry stump (roots and stems mass), if any. The number of larvae per stump and farm was recorded monthly. Larvae collected were measured (body length and width) and weighed in the laboratory. A subsample of the larvae collected of different sizes was used for DNA extraction and molecular identification using PCR.

There is hardly any information regarding how long larvae can feed on blueberries. Prionus imbricornis and P. pocularis larvae were confirmed through PCR conducted using larval DNA. One larva per plant was assumed as the damage threshold, as preliminary observations indicate that one larva feeding on one blueberry bush can damage the roots and crown enough to kill the plant. However, up to 16 larvae per plant were found feeding on a single plant during this study. Most of the stomps collected contained a range of 1-5 larvae. All larvae found in the stumps were collected alive, except for a few that died by accident during the process of opening the stumps apart using axes. Most of the larvae were found deep in the root masses. Only the smallest larvae were found in smaller shallow roots in the stumps. These smaller larvae were found during the stumps sampled in July and August (Table 3), and it is likely possible that these smallest larvae in shallow roots were newly hatched larvae from eggs laid during the emergence peak in May 2025. This is valuable information to consider when new insecticides become registered for Prionus beetles since the smallest larvae are the most vulnerable stage and the ones that should be targeted for chemical applications. Large larvae have been reported to be not susceptible to insecticides under laboratory conditions.

Sampson 1 and 2 were adjacent locations and showed the highest average weights among the collected larvae compared to Pender 1 (Table 4). It is important to note that weight and length of larvae can be influenced by many factors, including time of development on the plants, quality of the host, temperature, and humidity of the soil, among others. Further steps will taken to estimate the developmental instars of these larvae based on their body measurements.

We thank the NC Blueberry Council for its financial support in developing this monitoring program. Special thanks to the collaborating growers, Tiffanee Boone, Mark Seitz, Matt Strickland, and Brad Hardison (Pender, Sampson, and N.C. Cooperative Extension agents in Bladen County), and John Gardner (Horticultural Crops Research Station director) for their help servicing the traps at each location, and to Bill Cline and Gareth Powell's lab for his contributions to this program.

2025 Prionus Beetle Monitoring Program in Blueberries

The Root of the Problem: Prionus Longhorn Beetles in Blueberries (2024 Monitoring Program)

It Is Time to Scout for Prionus Beetles in Blueberries!