Additive Effect of Releasing Sterile Insects Plus Biocontrol Agents against Fruit Fly Pests (Diptera: Tephritidae) under Confined Conditions

SIMPLE SUMMARY: Theoretically, the joint use of augmentative biological control (ABC) and sterile insects (SIT) can generate an additive or synergistic effect on the control of fruit fly pests. Field cage evaluations demonstrated that the sequential use of both techniques on a confined population of Anastrepha ludens lead to greater suppression than each technique acting alone. This was observed with the use of the larval parasitoid Diachasmimorpha longicaudata (parasitism ~70%), as well as the pupal parasitoid Coptera haywardi (~35% parasitism), although the high parasitism percentages by D. longicaudata contributed a greater suppressive effect on the fly population. The joint use of ABC and SIT induced ~70% sterility in the A. ludens population; however, the impact on the reproduction parameters of the fly population suggest that the joint action of both techniques was synergistic. Decreases in the fertility rate and hatching percentage of A. ludens eggs resulted in a lower intrinsic rate of increase (up to 50%) in the fly population. ABSTRACT: Pest control models integrating the use of the sterile insect technique (SIT) and augmentative biological control (ABC) have postulated that it is possible to obtain a synergistic effect from the joint use of these technologies. This synergistic effect is attributed to the simultaneous attack on two different biological stages of the pest (immature and adult flies), which would produce higher suppression on the pest populations. Here we evaluated the effect of the joint application of sterile males of A. ludens of the genetic sexing strain Tap-7 along with two parasitoid species at the field cage level. The parasitoids D. longicaudata and C. haywardi were used separately to determine their effect on the suppression of the fly populations. Our results showed that egg hatching percentage was different between treatments, with the highest percentage in the control treatment and a gradual reduction in the treatments with only parasitoids or only sterile males. The greatest induction of sterility (i.e., the lowest egg hatching percentage) occurred with the joint use of ABC and SIT, demonstrating that the earlier parasitism caused by each parasitoid species was important reaching high levels of sterility. Gross fertility rate decreased up to 15 and 6 times when sterile flies were combined with D. longicaudata and C. haywardi, respectively. The higher parasitism by D. longicaudata was determinant in the decrease of this parameter and had a stronger effect when combined with the SIT. We conclude that the joint use of ABC and SIT on the A. ludens population had a direct additive effect, but a synergistic effect was observed in the parameters of population dynamics throughout the periodic releases of both types of insects. This effect can be of crucial importance in the suppression or eradication of fruit fly populations, with the added advantage of the low ecological impact that characterizes both techniques.