The number of mosquito populations resistant to insecticides is increasing along with the reemerging of vector-borne diseases. New technologies are under evaluation to complement the strategies used against these mosquitoes. Transgenic mosquitoes are one approach that some countries are considering and they are being evaluated to control the wild population. Although they have achieved success in population suppression of Aedes aegypti (L.) (Diptera: Culicidae), these studies have not demonstrated what the outcomes are when releases are interrupted (ceased). In this study, after demonstrating suppression of Ae. aegypti using transgenic technology, changes in the spatial distribution of the infestation and the abundance of the vector Ae. aegypti were assessed in the post-release period, along with fluctuation of transgenic mosquitoes in two areas of Brazil. In both pilot trials, there was an average suppression of ca. 70% of the wild population due to the release of transgenic males compared to the pre-release period. In Juazeiro (Mandacaru), in the post-release phase, the number of eggs per trap ranged between 0.06 and 14.41 (mean AE SE = 4.44 AE 0.44), and the ovitrap index (OI = number of ovitraps with eggs/total number of ovitraps recovered) ranged from 0.01 to 0.43 (0.13 AE 0.01). In Jacobina (Pedra Branca), during the post-release phase, the number of eggs per trap ranged between 1 and 7.2 (1.72 AE 0.72), and the OI ranged from 1 to 0.83 (0.095 AE 0.032). The mosquito population in Juazeiro (Mandacaru) remained suppressed for 17 weeks after the release interruption, whereas in Jacobina (Pedra Branca) suppression lasted 32 weeks. In Juazeiro, transgenic larvae were detected up to 5 months after the interruption of the over-flooding releases of transgenic males. In Jacobina, they were found up to 2 months after the release interruption. The number of eggs collected increased 4-5 months after the release interruption, which indicated that the Ae. aegypti population had been re-established after the interruption of releases. The results demonstrate that the technique requires a continuous release in the treated areas, and after suppression, the release rate can be decreased and used as a barrier against external migration.

The sterile insect technique (SIT) application, as an alternative tool for conventional mosquito control methods, has recently gained prominence. Nevertheless, some SIT components require further development, such as protocols under large-scale conditions, focusing on packing and shipping mosquitoes, and considering transporting time. Immobilization of Aedes aegypti males was tested at temperatures 4, 7, 10, and 14 °C, and each temperature was assessed for 60, 90, and 120 min. The recovery after 24 h was also studied. Chilled and control-reared males had comparable survival rates for all conditions, although 4 °C for 120 min impacted male survival. The male escape rate was affected after 60 min of exposure at 4 °C; this difference was not significant, with 24 h of recovery. First, we defined the successful immobilization at 4 °C for 60 min, thus enabling the evaluation of two transportation intervals: 6 and 24 h, with the assessment of different compaction densities of 100 and 150 mosquitoes/cm3 at 10 °C to optimize the shipment. Compaction during simulated mosquito shipments reduced survival rates significantly after 6 and 24 h. In the mating propensity and insemination experiments, the sterile males managed to inseminate 40 to 66% for all treatments in laboratory conditions. The male insemination propensity was affected only by the highest compaction condition concerning the control. The analysis of the densities (100 and 150 males/cm3) showed that a higher density combined with an extended shipment period (24 h) negatively impacted the percentage of inseminated females. The results are very helpful in developing and improving the SIT packing and shipment protocols. Further studies are required to evaluate all combined parameters’ synergetic effects that can combine irradiation to assess sexual competitiveness when sterile males are released into the field.

The success of the sterile insect technique (SIT) depends on the ability of sterile males to compete effectively with wild males to mate with wild females. This study compared the sexual competitiveness and other behavioral parameters of males of two strains of Ceratitis capitata (Wiedemann) (Diptera: Tephritidae), tsl Vienna 8 (tsl V-8) and the transgenic line OX3864A, in competition with wild males from the São Francisco Valley region in Bahia, Brazil. Mating events were observed in field cages containing virgin, sexually mature insects as follows: 50 wild females (10-12 days old), 50 wild males (8-10 days old), and either 50 tsl V-8 sterile males (5 days old) or 50 transgenic males (3-4 days old). In addition to scoring male type for each mating event, we also monitored the location of mating events within the tree canopy, mating duration, and mating latency. The proportion of females that mated did not differ between the two competition scenarios tested (tsl V-8 vs. wild males: 0.65 AE 0.04; transgenic vs. wild males: 0.64 AE 0.03). Relative sterility index did not differ between sterile (0.34 AE 0.04) and transgenic males (0.31 AE 0.03). The latency period was significantly longer for transgenic males (84.90 AE 4.87 min) than for sterile (65.24 AE 4.65 min) and wild males (66.61 AE 2.66 min). Mating events involving the three strains occurred in the same area of the tree, i.e., mid-height, in the central sector and on leaf undersurfaces. The mean duration of mating events involving sterile (94.1 AE 3.59 min) and transgenic males (81.1 AE 3.54 min) were both significantly shorter than for wild males (123.3 AE 1.93 min). Further investigation is suggested to assess other behavioral parameters, such as the amount of sperm transferred by transgenic males, their ability to disperse and survive in the field conditions, and their capacity to prevent females remating with wild males, in order to determine the potential of this transgenic strain for inclusion in the Brazilian SIT programs.

Studies investigating oviposition preference of Ceratitis capitata (Wiedemann, 1824) in table grapes (Vitis vinifera L.) cultivated in the São Francisco River Valley can provide important information to guide control measures, therefore minimizing damage caused by this species in the region. The aim of this study was to evaluate the oviposition preference of C. capitata females for berries cv. ‘Italia’ collected at five different times (60, 70, 80, 90, and 100 d after production pruning [DAPP]), representing five grapevine growth stages. We also assessed the performance of immature stages of C. capitata regarding the physiological development of the berry. The total soluble solid content was significantly higher in berries at more advanced physiological developmental stages (90 and 100 DAPP). Conversely, these berries showed the lowest values of firmness and titratable acidity. With the onset of physiological development, the average number of punctures per berry increased and reached 5.2 per berry in 100 DAPP berries. The infestation level and pupal weight showed a positive correlation with the growth stage. The highest recovery of pupae was observed in 100 DAPP berries (1.54). Pupal viability values ranged from 50.9 to 64.7% independent of berry maturity stage. The physiological developmental stage of the berry did not affect offspring sex ratio. Results obtained suggest that regardless of the female preference for laying eggs on berries in a more advanced physiological developmental stage, females can initiate the attack to bunches of this cultivar at 60 DAPP, even if the berries have unfavorable physicochemical parameters for oviposition and development of larvae.