In this work we demonstrate that when Ae. aegypti larvae was parasitized by A. taiwanensis and exposed to the oil of Az. indica or to the organophosphate Temephos induce a higher mortality. Mosquitos’ mortality (parasitized males and females) was 73%, while mortality of the non-parasitized was 44%. These results are like those reported by [32, 33], which obtained reduction in the longevity for Ae. aegypti parasitized by A. culicis and Ochlerotatus triseriatus parasitized by Ascogregarina barretti. These authors also observed prolongation of the larval stage and reduction of adult size for both species of mosquitoes [32, 33]. [34], observed that Ae. albopictus parasitized by Ascogregarina sp. presented higher mortality of immature stages when larvae were under nutrient. These morphological observations in all protozoa stages were like that found by Lien and Levin (1980).
These results are like those obtained by Comiskey et al. (1999), were Ae. albopictus parasitized by Ascogregarina sp., presented a decrease in the reproductive capacity of females, even with high nutrient conditions. The synergism between microorganisms and insecticides inducing higher mortality was also reported by [14]. This author verified that when larvae of Ae. aegypti were exposed to Az. indica and the fungus Metarhizium anisopliae (5×105 conidia/mL) presented higher mortality. Similarly, [13] observed that when Bacillus thuringiensis var. israelensis is used with Temephos in Ae. aegypti, a 90% greater larval mortality is obtained in the first hour of exposure, compared to the group treated with Temephos alone.
The compounds of Az. indica have several forms of action, which may act in an antiparasitic, antihelmintic, antimicrobial and other forms [35, 36]. In the present work, the higher mortality of parasitized Ae. aegypti when exposed to Az. indica may be related to antiparasitic action. According to [37], extreme variations of physiological conditions in association with parasitic infection can cause necrosis in the cells, resulting in direct damage to the plasma membranes of the host. Thus, we can suggest that if there was an antiparasitic action of Az. indica on the gregarine facilitated the insecticidal activity of this oil on the larvae.
Although the A. indica concentration is higher than Temephos in the dosage values, it is noteworthy that there are reports that the survival of Ae. aegypti exposed to more than 0.02 mg/L of Temephos indicates the possibility of resistance among the population tested (Brown, 1986; Denham et al. 2015; Arslan et al. 2015).
According to [38] new methods for Aedes vector control aimed at reducing the use of chemical insecticides should be urgently prioritized. Thus, we believe that integrated and interleaved control may also reduce the pressure on the selection of individuals who are resistant to routinely used chemical insecticides. The results obtained, indicate that A. taiwanensis negatively influences its host, in this case both Ae. albopictus as Ae. aegypti. In this way, we believe that this gregarine has potential for biological control of vectors.
The synergism between microorganisms and insecticides inducing higher mortality was also reported by [14]. This author verified that when larvae of Ae. aegypti were exposed to Az. indica and the fungus Metarhizium anisopliae (5×105 conidia/mL) presented higher mortality. Similarly, Andrande and Modolo (1991) observed that when Bacillus thuringiensis var. israelensis is used with Temephos in Ae. aegypti, a 90% greater larval mortality is obtained in the first hour of exposure, compared to the group treated with Temephos alone. Interestingly, it has also been reported that Ae. albopictus infected with Ascogregarina reduces its competitiveness in the habitat with different larvae such as Ae. triseriatus [39]. In addition, it has already been shown that the propitious infection by Ascogregarinas can impact the Ae. Albopicuts microbiota. [40].
The compounds of Az. indica have several forms of action, which may act in an antiparasitic, antihelmintic, antimicrobial and other forms [35, 36]. In the present work, the higher mortality of parasitized Ae. aegypti when exposed to Az. indica may be related to antiparasitic action. According to Golstein and Kroemer (2007), extreme variations of physiological conditions in association with parasitic infection can cause necrosis in the cells, resulting in direct damage to the plasma membranes of the host. Thus, we can suggest that if there was an antiparasitic action of Az. indica on the gregarine facilitated the insecticidal activity of this oil on the larvae. Although the A. indica concentration is higher than Temephos in the dosage values, it is noteworthy that there are reports that the survival of Ae. aegypti exposed to more than 0.02 mg/L of Temephos indicates the possibility of resistance among the population tested [41–43]
According to Guirado and Bicudo, (2009) new methods for Aedes vector control aimed at reducing the use of chemical insecticides should be urgently prioritized. Thus, we believe that integrated and interleaved control may also reduce the pressure on the selection of individuals who are resistant to routinely used chemical insecticides. The results obtained, indicate that A. taiwanensis negatively influences its host, in this case both Ae. albopictus as Ae. aegypti. In this way, we believe that this gregarine has potential for biological control of vectors.