Field assessment of 3 years of releases of substerile males of Ectomyelois ceratoniae (Lepidoptera: Pyralidae)

Full text: Male Ectomyelois ceratoniae were released weekly in a pomegranate orchard during three years. Irradiation was done using a Co60 source with a dose rate of 46 Gy/min. The gamma radiation substerilising dose adopted for this programme was 400 Gy. The efficiency of these releases was investigated at the harvest. Releases of the substerile male insects preceded the start of the wild population activity. The monitoring of the wild pest population was accomplished using a series of Delta traps baited with the sex pheromone of the insect. Traps were kept in the field the whole season. Trapping results and sampling data were used in order to study the population dynamics of the insect. We studied male dispersion, the competitiveness in the field and attractiveness of irradiated virgin female of the reared and irradiated male moth. At the harvest, we determined the fruit infestation-rate both in the treated orchard and in the control. Irradiated male dispersion was studied using 24 delta traps. The experimentation was conduced each season. Six levels of male capture were chosen. These distances were 20, 40, 60, 80, 100 and 120 m from the point release. Results showed that irradiation at the substerilising dose 400 Gy did not affect the male's ability of flying. Moreover, we observed that irradiated males were able to reach traps placed at 120 m from the released point. Most of the insects were captured at 40m and 80m. This result is very important and has a practical implication. In fact, in order to get a homogeneous distribution of the sterile male moths in the field, distances between 40m and 80 m should be kept between the release-lines. Studies on the male's competitiveness were carried out in two cages. The cages contained two middle size trees and were covered with a mosquito net. A delta trap was hung into each cage. The trap was baited with two virgin non-irradiated females. Four ratios of irradiated to untreated males were investigated: 1:1, 2.5:1, 5:1 and 10:1. Experimentations were replicated five times for each ratio. Results showed that substeriles males of Ectomyelois ceratoniae are competitive under field conditions at all tested ratios. Moreover, at the ratio 1:1 irradiated males were 48% competitive. Attractiveness of irradiated virgin females was compared to virgin untreated females and to the synthetic pheromone lure. After radiation, the virgin females were used to bait delta traps. They were replaced weekly. Attractiveness was assessed by the ability of irradiated females to attract males. It was observed that they were as attractive as the untreated ones. Furthermore, virgin irradiated females were more effective than the synthetic lure. Insect infestation at harvest was evaluated by counting the damaged fruits. Pomegranates infested by the carob moth E. ceratoniae are often rotten with the insect inside. Each year, 500 trees were counted in order to assess the efficiency of the releases. Trees were chosen randomly among the five ha orchard. After three years of season-long releases, we get a notable reduction of the fruit infestation. In addition, we can predict that the use of the SIT technique presents an important potential in the suppression of the wild population of E. ceratoniae. Actually, this procedure could be adopted to control this insect pest on palm trees in southern Tunisia. (author)