Hemp tumbling flower beetle

The hemp tumbling flower beetle (Mordellistena cannabisi) is a small beetle belonging to the Mordellidae family, which are commonly known as tumbling flower beetles due to their erratic movement.

Adult beetles measure between 3 to 5 millimeters in length. Their bodies have a characteristic humpbacked shape, tapering towards the posterior end, which is a diagnostic feature of the family.

Their color typically ranges from dark brown to black, often covered with fine, dense setae or hairs that give them a matte appearance. They are agile insects capable of jumping when disturbed.

The larvae are typically whitish, soft-bodied, and feature well-developed mouthparts that enable them to bore into the stems of their host plants.

As specialists in the hemp ecosystem, their entire life cycle is tightly coupled with the phenology of hemp cultivation, making them a significant agricultural pest.

This beetle primarily affects industrial hemp crops, with both fiber and grain varieties being susceptible to larval infestation.

The larvae are the destructive stage of the pest; they burrow into the stem, creating longitudinal galleries within the pith. This mining activity disrupts the plant's vascular system.

As a result, the flow of nutrients and water is impeded, leading to plant wilting, stunted growth, and a marked reduction in overall yield.

Stems damaged by the larvae often become structurally unstable, leading to lodging, where plants bend or break in the wind, which complicates harvesting operations.

Furthermore, the physical injury to the stems facilitates the entry of secondary pathogens, including fungi and bacteria, which can cause stem rot and total plant collapse.

The adult beetles emerge and become active during the warmer summer months, precisely when the hemp plants are in their peak vegetative growth or early flowering stages.

Mating and oviposition occur on the stems or leaf axils, and shortly after hatching, the young larvae tunnel into the host plant's internal tissues.

The larvae remain protected inside the stems for the duration of the summer, feeding and molting until they reach maturity in late summer or early autumn.

Pupation takes place inside the stem galleries, and the pest overwinters within these residues or in the soil, waiting for the return of favorable conditions in the next growing season.

Given this one-generation-per-year life cycle, intervention at the end of the harvest is crucial to reduce the overwintering population for the next year.

The earliest signs of infestation include small, round boreholes on the stem surface, sometimes accompanied by slight darkening or discoloration of the tissue.

General symptoms observed in the field include premature yellowing of foliage and localized patches where hemp plants appear shorter or weaker than the surrounding crop.

One of the most obvious signs is the unexpected breaking of stems in the middle of the growing season, which indicates that the internal pith has been hollowed out by larvae.

By splitting a damaged stem, one can clearly see the tunnels filled with frass, the waste product left behind by the larvae as they feed.

Active adult beetles can often be spotted congregating on the upper leaves or flowers during sunny, calm days in mid-summer.

Deep plowing after harvest is the most effective cultural control method, as it buries infested crop residues, preventing the emergence of adults the following spring.

Implementing a robust crop rotation strategy is essential; avoiding hemp cultivation on the same plot for multiple years will significantly decrease the local beetle population.

Ensuring that all crop residues are cleared and destroyed reduces the available overwintering sites, which is vital for preventing re-infestation.

In cases of severe outbreaks, systemic insecticides may be employed to target adults before they lay eggs or before the larvae successfully penetrate the plant stems.

• Monitor field edges for adult beetle activity during the vegetative phase.
• Select resistant hemp cultivars if available in your region.
• Maintain healthy crop density to minimize the impact of individual plant losses.