UV reflective properties of magnesium oxide increase attraction and probing behavior of Asian citrus psyllids (Hemiptera: Liviidae)

Abstract

Asian citrus psyllid (Diaphorina citri) vectors the bacterium Candidatus Liberibacter asiaticus, the causal pathogen of citrus greening disease that is devastating citrus industries worldwide. Suppressing psyllid populations is crucial to prevent disease spread. An attract-and-kill trap based on psyllid behavior would fill a niche for monitoring and control. To optimize visual attraction of psyllids, the ultraviolet (UV) reflective properties of magnesium oxide (MgO) and/or barium sulfate (BaSO 4) were assessed for potential application to a trap surface. Under low UV, high UV and natural sunlight conditions, the reflectance, attraction, and probing behaviors of psyllids were evaluated on surfaces containing magnesium oxide or barium sulfate. Magnesium oxide added to yellow sticky traps enhanced visual response of D. citri. Probing assays demonstrated that magnesium oxide alone or as a mixture with a phagostimulant blend, increased the UV reflectance of substrates, as well as, attraction and probing by psyllids. Results demonstrated that psyllids respond to both short (UV) and long (yellow) wavelengths during orientation, and that these inert compounds can increase UV reflectance and improve attractiveness of an attract-and-kill device.

Attributes of Yellow Traps Affecting Attraction of Diaphorina citri (Hemiptera: Liviidae)

“…Reflectance of MgO was high (>96%) between 300 and 700 nm ( Figure 4 ) and similar to that reported by George et al [ 9 ]. In experiment 6, the addition of MgO (1.25 to 3.75 g) did not enhance attraction to Olson yellow traps (F = 1.162; df = 3, 47; p = 0.335) ( Table 4 ).…”

“…Responses of D. citri to white traps [ 16 ] as well as white LEDs [ 17 ] are generally low. However, with the recent discovery that UV reflectance plays an important role in attraction to specific colors such as yellow or green [ 9 , 18 ], the potential for enhancing attraction to white through use of UV reflection was examined with white decoy paint. Additionally, the enhanced reflectance or intensity from white surfaces was examined with use of fluorescent white paint.…”

“…The concept of combinating UV and yellow as an attractant for bees was termed “bee purple” by Daumer [ 78 ] and was also demonstrated as important in attraction of Heliconius erato scales [ 61 ]. Addition of a UV-reflecting pigment, magnesium oxide, to decoy yellow targets enhanced attraction of D. citri [ 9 ]. When magnesium oxide was added to phagostimulant blends of chemicals, attraction and probing by D. citri were increased [ 9 ].…”

“…There is strong evidence that adult D. citri primarily use visual cues to orient at a distance to, and gustatory cues to settle on, host plants [ 8 , 9 , 10 ]. Olfactory orientation has not been conclusively demonstrated despite attempts to do so [ 8 , 10 , 11 , 12 , 13 , 14 ].…”

“…The removal of UV wavelengths from green or yellow light significantly reduced attraction, indicating that UV wavelengths may play a role in attraction to long wavelengths [ 19 ]. Addition of a UV-reflecting pigment, magnesium oxide (MgO), increased attraction to yellow traps in the laboratory and field and enhanced probing behavior when combined in a phagostimulant blend [ 9 ]. Female D. citri prefer emergent citrus leaves before they are fully expanded for feeding and oviposition and these leaves are characteristically high-intensity yellow/green [ 16 , 18 ].…”