[Copesan University] When Do Red Flour Beetles Fly?

When insect resources become scarce and their populations increase, only dispersal to new habitats ensures possible insect population survival. In fact, the ability of the red flour beetle (Tribolium castaneum [Herbst]) to disperse by flight and colonize new food supplies has contributed to its status as a costly economic pest throughout the world.

TRIGGERING FLIGHT ACTIVITY. Following are factors that trigger flight behavior for the red flour beetle:

Typical flight activity. Male and female red flour beetle adults normally can fly 48 hours after adult emergence. Newly emerged females (two to 10 days old) tend to fly more than newly emerged males, suggesting that males initially prefer to stay in the breeding media, waiting to mate with freshly emerged virgin females. After this period of time, the flight behavior of both males and females tends to be similar.

Contrary to other stored product pests, whose optimum chronological age range for flight activity is between the first two to five days (e.g., lesser grain borer) or four to 32 days (e.g., larger grain borer) after adult emergence, red flour beetle adults are able to fly during their entire life span. However, their maximum peak of flight activity occurs in relatively young adults, and mated males and females tend to fly more than virgin ones.

Food supply. The amount and quality of food in the environment has a high influence on flight. Red flour beetle adults with plenty of food for oviposition and larval development are less likely to fly, but when food is absent or scarce, flight is their predominant behavior.

Therefore, reproductively active adult beetles in food and processed grain storages respond to depleting resources at the end of the storage season by flying to new environments where resources are better for reproduction. These new environments may be located within the same facility or at other facilities.

Temperature and light. Temperature and photoperiod (light) trigger flight in numerous insect species. Generally, temperature affects the number of insects flying, while photoperiod influences the time of flight.

Red flour beetles rarely fly when temperatures are below 20°C (68°F). The optimal temperatures for flying in this species range from 25 to 35°C (77 to 95°F), but flight can occur even at 40°C (104°F). Photoperiod doesn’t have a big influence on the flying behavior of red flour beetles because adult activity occurs at every hour of the day and night, with more flight activity typically observed at dusk.

PRACTICAL IMPLICATIONS. The role of male-produced aggregation pheromones may be to congregate males and females at a new suitable food resource. Thus, we can expect that the insects caught by aerial pheromone-baited traps are most likely to be active young beetles seeking new food resources to infest.

In contrast, the absence of red flour beetles in a monitoring trap, when red flour beetles are present, could indicate that sufficient food resources are available. Similarly, not seeing red flour beetles flying when large numbers of beetles are present in terrestrial pheromone-baited traps and all other factors are favorable for flight, may also indicate that sufficient food resources are available. Certainly, this research raises some questions on the value of visual inspection and flour beetle monitoring traps. For example, capturing red flour beetles on or off the floor may mean that sanitation programs are working. Captures also may be a trigger for implementing pest management strategies to prevent infestation of uninfested products by this pest.

Editor’s note: The information provided here is part of a research project conducted by the author and James E. Throne, James E. Campbell and Paul Flinn at the USDA-Grain Marketing Production & Research Center. Their goal was to determine the importance of various flight stimuli to find out when red flour beetles fly.

The author is technical and training director, Schendel Pest Services, Topeka, Kan.