Visual cues are relevant in behavioral control measures for new Guinea sugarcane weevil (Rhabdoscelus obscurus (Coleoptera: Curculionidae)

Background/Question/Methods

The New Guinea sugarcane weevil (Rhabdoscelus obscurus) (Coleoptera:  Curculionidae) is a pest of palm plantations, ornamental nurseries, and sugarcane. This weevil is a very serious pest of ornamental palms and coconut plantations in the Mariana Islands and other Pacific islands. Few data are available on the monitoring of R. obscurus with pheromone traps, so improving trap performance and making traps more reliable tools for integrated control programs will require characterizing the factors that affect trap capture efficiency. Traps for R. obscurus have relied primarily on chemical cues, while our results indicate that these borers also rely on visual cues. Previous studies  have demonstrated that among the eight differently colored traps tested in the field, brown colored traps were the most effective, compared with the performances of yellow, red, grey, blue, black, white, and green traps; russet was more effective than other shades of brown. Field and laboratory studies have explored the effects of visual and olfactory cues on trap capture efficiency in date palm plantations and ornamental on Guam. The weevil’s response to pheromone-baited ground traps of several different colors (used either individually or as 50:50 mixtures of two different colors) were compared with the standardized russet-brown traps.

Results/Conclusions

Traps with brown mixed with different colors, had no significant effect. In contrast, a laboratory color-choice tests indicated, R. Obscurus preferred black traps over other color traps, with no preference among different shades of black. Here again, traps either solely black or mixed (50:50) with different colors had any influence on the catches. Therefore, any other color that mixes with mahogany brown or black would dilute the attractiveness of the specific color and give a lower catch and that this effect would be color dependent. By exploiting these results, it may be possible to produce efficacious trapping systems that could be used in a behavioral approach to New Guinea sugarcane weevil control. We also hypothesize that any other color that mixes with russet brown would dilute the attractiveness of the brown and give a lower catch in the field and that this effect would be color dependent i.e. Mixing in gray would have a different dilution effect than mixing in yellow, etc.  Similarly, any other color that mixes with black would dilute the attractiveness of the black and give a lesser catch in the laboratory.