Development of the sterile insect technique as a control strategy for the Asian citrus psyllid: determining the number of sterile individuals needed to suppress the growth of wild populations

Controlling the Asian citrus psyllid (ACP), Diaphorina citri, is key to preventing spread of huanglongbing, a disease that has decimated citrus industries worldwide. One promising control method is the Sterile Insect Technique (SIT). This involves rearing large numbers of a target pest, sterilizing them using radiation, and releasing them into the field to compete with wild conspecifics for mating, ultimately suppressing population growth. The success of SIT is largely influenced by 3 factors: (i) ensuring released insects are sufficiently sterile such that mating between wild and sterile individuals yields no (or very few) offspring; (ii) ensuring the ratio of sterile to wild insects released (the overflooding ratio [OFR]) is sufficient to minimize the occurrence of mating between 2 wild individuals; and (iii) ensuring the released insects are competitive with respect to mating performance, dispersal, and longevity. Previously, we tentatively identified that a 320 Gy dose of X-ray radiation was required to sterilize ACP. Herein we investigate the impact of OFR on the growth of caged populations. Laboratory-cage experiments suggested that following sterilization with 240 or 320 Gy, a single release of ACP at OFRs of 10:1 and 15:1, could effectively suppress subsequent growth of ACP populations. To validate this finding under more natural conditions, we repeated the experiments using mature citrus trees held within field-cages. We found that a sterilizing dose of 320 Gy of X-ray radiation had the greatest impact in the field-cages, with an increase in the OFR from 10:1 to 15:1 showing only a marginal additional benefit.