Sex pheromone and ultraviolet radiation: interaction of attraction effects for cotton earworm, <i>Helicoverpa armigera</i> (Hbn.) (Lepidoptera, Noctuidae) adults

Although the potential of the use of the semiochemicals (pheromones, allomones, kairomones, and synomones) and the semiophysicals (physical stimuli) to control insect behaviour for plant protection from harmful insects is beyond doubt, the characteristics of the interactions between their attractive properties have been extremely poorly studied. Therefore, despite the fact that the cotton bollworm, Helicoverpa armigera, is one of the most harmful insects on the planet, there is no information in the literature on the effect of a combination of light stimuli and a synthetic sex attractant (SSA) on the behaviour of this species. In July–August 2021–2023, we conducted a study in two locations in Krasnodar Territory of Russia to test attraction of cotton bollworm adults with traps placed on corn sowings and equipped with four baits: (1) ultraviolet light emitting diodes (UV LEDs), (2) SSA, (3) SSA + UV LEDs, and control (4). The results obtained showed significant differences between the baits in capturing moths: not a single adult was captured in the control trap at all; traps with UV LEDs captured about 8%; with SSA, capturing a little more than 30%, and traps that attracted insects with both SPA and UV LEDs captured almost 60% of the total number of moths captured. The small catch of moths to the light is clearly explained by the situation of the traps in rows of tall hybrid corn at a height of 1.5 metres above the ground and no closer than 30 metеrs to the edge of the field. This means that the light, unlike SSA signals, was faded rapidly by the surrounding vegetation. However, a positive aspect of the technique used is the absence of significant numbers of non-target insect species capture in traps. The only exceptions are green grasshoppers, Tettigonia caudata (Ch.) and T. viridissima (L.), in traps with LEDs or other baits. Using two-factor ANOVA of both the original and transformed (x + 0.5)½ capture data, we found a synergy effect in the interaction of SSA and LED signals with respect to attractiveness for pest adults at pa = 0.05 only in one out of the five tests conducted. This result shows that the interaction of the semiochemicals and semiophysicals has rather additive than synergistic nature. Nevertheless, the results of the tests suggest that the combined use of SSA and LED may be a promising means for controlling the behaviour of the pest since retrofitting pheromone traps with UV LEDs can result in an approximately twofold increase in catch rates of the cotton bollworm adults.