Cold acclimation strengthens Plodia interpunctella in warehouses

Study reveals that the insect Plodia punctella, known as the grain moth, can develop greater cold tolerance after brief exposure to low temperatures. This finding raises concerns about the effectiveness of cold storage as a pest control method for stored grains.

The researchers subjected the insects to a 15-hour acclimatization period at 4°C. After this period, they observed significant improvements in cold tolerance, as well as changes in the pest's development and reproduction. The results indicate that, contrary to expectations, low temperatures may strengthen the insect rather than eliminate it.

The plague and the problem

Plodia punctella It is a cosmopolitan pest with a high reproductive capacity. Its damage occurs primarily in the larval stage, when individuals form webs that clump together grains, promoting moisture accumulation and promoting fungal growth.

With growing resistance to fumigants like phosphine and the limitations of alternative methods, such as low-oxygen atmospheres, the use of low temperatures has been adopted by many warehouses. However, this strategy may be less effective than previously thought.

Effects of acclimatization

During the experiment, researchers observed a significant drop in the superfreezing point (SCP) of the insect's larvae and pupae. This point determines the temperature at which the body spontaneously freezes. Fourth-instar larvae showed the greatest reduction in SCP, indicating a significant increase in cold tolerance.

Furthermore, exposure to cold activated the insect's antioxidant system. The activity of the enzymes superoxide dismutase (SOD), catalase (CAT), and peroxidase (POD) increased at all stages of development, especially in larvae. These enzymes protect cells against oxidative stress caused by low temperatures.

Greater fertility

Insects acclimated to cold conditions exhibited faster development at moderate temperatures. The pupal stage, for example, was reduced by almost a day at 24°C. The adult stage, however, was reduced by about 6 hours. The total life cycle length dropped from 64,6 to 62,3 days.

Another relevant finding concerns fertility. Cold-acclimated females produced more eggs (312, on average) than non-acclimated females (273) at 24°C. The difference was statistically significant. At higher temperatures (28 and 32°C), acclimation did not cause significant changes in reproduction.

Darker pigmentation

After exposure to cold, the larvae developed a darker body color. Second-instar larvae went from light pink to purplish hues, while fourth-instar larvae went from pale yellow to gray. This change may be related to the body's thermal regulation, as dark pigmentation absorbs more heat.

Pest control

The study concludes that cold acclimation can pose a challenge to low-temperature control. The pest's physiological responses indicate that prior exposure to cold may induce defense mechanisms that make it more resistant to this type of environment.

This adaptation may reduce the effectiveness of cold storage techniques, especially in environments with temperature fluctuations. Because the experiment was conducted under controlled laboratory conditions, the authors recommend further research in real-world environments, with diurnal and seasonal temperature cycles, to assess the practical impact of the findings.

Further information at doi.org/10.3390/insects16090927