Larval feeding is the most damaging stage of the clover root curculio (Sitona hispidulus). Underground feeding from clover root curculio larvae progresses from nitrogen-fixing nodules to the cortex of the taproot. This kind of damage does not kill the plant outright but instead accumulates over time and can cause chronic issues such as decreased stand establishment, density, and stand life. (Photo credit: Steven Price)

By Kaitlin Rim

Many think of the alfalfa weevil (Hypera postica) as the characteristic alfalfa pest weevil, but another noteworthy weevil causes damage to alfalfa and clover stands throughout North America: The clover root curculio (Sitona hispidulus), which was first discovered in New Jersey in 1875, has been overlooked as a pest in forage systems for decades. A new resource on clover root curculio published this month in the open-access Journal of Integrated Pest Management is the first review of this pest since the mid-1900s.

Kaitlin Rim

In, “Biology and Management of Clover Root Curculio (Coleoptera: Curculionidae),” my colleagues Steven Price, Erik Wenninger, Rachael Long, and Ricardo Ramirez and I discuss what is currently known about clover root curculio (CRC) biology, damage, ecology, and management. Many types of cultural, biological, and chemical control methods have been researched historically, and we evaluate the practicality of these methods in contemporary forage systems. However, there is a need to adapt and improve historic monitoring and management techniques. Currently, there are no established economic thresholds, no predictive degree day models, nor registered insecticides that target the damaging larvae.

What makes CRC so difficult to monitor, research, and manage is that the damaging larval stages feed cryptically underground on alfalfa and clover roots. Larval feeding, leads to a myriad of issues in alfalfa and clover production such as increased winterkill, shortened stand life, reduced stand establishment and density, and decreased water and nutrient uptake. These issues culminate in reductions in forage quality and yield over time. Most importantly, synergism of CRC feeding damage and secondary plant pathogens can decrease yield by two- or three-fold when compared to damage from each pest alone.

The clover root curculio (Sitona hispidulus) is a pest of alfalfa and clovers. A new profile article published in the Journal of Integrated Pest Management outlines clover root curculio identification, biology, and ecology and highlights where research is needed to improve management techniques. The adult feeds on foliage and causes minimal damage. (Photo credit: Steven Price)

Historically, chemical insecticides used against alfalfa weevil indirectly suppressed CRC populations. However, since most of these insecticides were banned in the early 20th century, CRC populations have resurged. Clover root curculio can be hard to detect, especially the immature stages occurring underground. Overlooking CRC damage is common because we don’t always think to investigate what’s happening underground. Our new publication in the Journal of Integrated Pest Management (JIPM) presents many ways to monitor for CRC and identify associated damage.

Despite the lack of chemical control options, other methods such as resistant host plants, crop rotation, and biological control may help to suppress CRC populations. When collecting and surveying CRC for research, Steven Price and I often observe CRC adults and larvae naturally infected with fungi in the field. Biocontrol with entomopathogens may be a promising CRC management tactic for immature populations. Investigations into biocontrol of CRC using entomopathogens are underway.

Clover root curculio larval damage is often unnoticed or is mischaracterized as damage from other pests or abiotic factors. Therefore, damage may be more frequent than actually reported. It is difficult to know in which growing regions CRC is currently causing major problems; however, we believe that damage at some level occurs in most alfalfa and clover fields throughout North America. This article in JIPM aims to increase awareness of CRC and its associated damage and, moreover, to open a dialogue regarding potential management techniques and inspire future research into clover root curculio.

Kaitlin Rim is a master’s student in ecology at Utah State University’s Department of Biology. Email: krim19@aggiemail.usu.edu.