Studying on possibility of use of a rice fields active aquatic moth in biological control of aquatic weeds, Azolla filiculoides Lamarck and Azolla pinnata R. Brown in paddy fields of northern Iran

Farahpour-Haghani, Atousa and Hassanpour, Mahdi and Alinia, Faramarz and Nouri Ganbalani, Gadir and Razmjou, Jabraeil (2018) Studying on possibility of use of a rice fields active aquatic moth in biological control of aquatic weeds, Azolla filiculoides Lamarck and Azolla pinnata R. Brown in paddy fields of northern Iran. Doctoral thesis, University of Mohaghegh Ardabili.

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Abstract

Research Aim: Azolla filiculoides Lamarck and Azolla pinnata R. Brown have been reported as two most important invasive Azolla spp. aquatic ferns worldwide and it there is evidence that both species exist in Iran. Azolla spp. Cataclysta lemnata is an aquatic moth with shelter making behavior and during some surveys in northern region of Iran, high density populations of this moth found on water fern (Azolla spp.: Azolaceae). The possibility of use of this moth for biological control of both Azolla species in northern regions is the aim of recent research. Research method: This moth has been reported on many aquatic plants but Lemnaceae(duckweeds) are known as main host plant of this moth. In order to evaluate possibility of use of this moth for biological control of water fern, biology of the moth on water fern and duckweed, host range and host preference in paddy fields, efficacy and seasonal changes in adults and larvae population density were studied. Findings: Study of C. lemnata biology showed that the percentages of survival on Azolla spp. were 41-84 and on duckweeds were 61- 15%. Under laboratory conditions, larvae that reared on A. pinnata and L. minor, with 39.17 and 31.08 days, had the highest and the lowest development time, respectively. The average fertility on Azolla spp. and duckweed were 234.71 and 433.82 eggs per female, respectively. The highest and lowest daily food consumption were 3.13 mg and 1.64 mg, which were measured for the larvae reared on A. pinnata and L. minor. The average survival rate on different plants was 0-10%. The maximum and minimum number of larvae per unit area was 254 and 1 larvae per square, which were recorded in March and October. Conclusion: Results indicated that C. lemnata can be considered as a biological control agent for Azolla spp. Guilan province. This moth is fitted to feed on Azolla spp. very well. However, through the fitness process development time increased and fertility decreased. Nevertheless, these changes increased efficacy of the moth as biological control agent for Azolla spp. host range studies indicated that despite of the general idea about this moth, it is not polyphagous species, but in absence of main host plant it can survive by saprophytic feeding behavior on other macrophytes. However, it is not able to cause serious damage on fresh plants. Duckweed is preferred host plant for both feeding and oviposition. However, it is not suitable host plant for the moth anymore and feeding on this host plant is going to cause sever mortality in the moth colonies. In addition, results indicated that the moth is more effective on A. pinnata which is most abundant species in rice fields, compare with A. filiculoides. Seasonal change in population density and efficacy showed that larvae population density during the most active feeing period is not enough for wiping the water surface and this is main reason for the failure of the moth on Azolla spp. control in recent years. Therefore, increasing population density to effective level by mass rearing and releasing the larvae during the most active feeding period would be resulted in Azolla spp. control in these areas. In rice fields considering to limited cropping period and faster activity of the larvae in spring, spring larvae releasing would be more suitable. In wetlands due to annual existence of Azolla spp. and slower and more regular activity of the larvae in autumn, larvae releasing in autumn would be more beneficial. Nevertheless, considering time limitation of this study, more laboratory and filed studies need to determine the appropriate density and mass rearing methods for this moth and recent study would be main reference for future studies.

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