Biocontrol efficiency of Neoseiulus longispinosus evans (Mesostigmata:Phytoseiidae) against Tetranychus gloveri banks (Prostigmata:Tetranychidae) on Adenium obsesum (Forssk.) roem. & schult.

Abstract

Adenium obesum (Forssk.) Roem. & Schult. is a highly demanded ornamental plant in the floriculture industry. As this plant requires low maintenance, the popularity of this ornamental is widely increasing. Recently, the spider mite species, Tetranychus gloveri Banks has emerged as a serious pest on adenium in the ornamental nurseries of Kerala. The mite species has developed a significant level of resistance to commonly used synthetic acaricides, making mite management difficult in commercial horticultural nurseries. This demands the search for more viable alternative control strategies. Biological control offers a safer substitute for chemical acaricides to manage mite pests. The predatory mites of the family Phytoseiidae constitute a sizeable proportion of effective natural enemies commercially used as biocontrol agents. Among phytoseiid mite species, Neoseiulus longispinosus Evans, has been reported as a potential biocontrol agent against several spider mite species. A study was carried out in the Insectary and the Acarology Laboratory, Department of Agricultural Entomology, College of Agriculture, Vellanikkara, during the period 2022 2024 to investigate the biology of T. gloveri on adenium, the biology of N. longispinosus on T. gloveri, the predatory potential of N. longispinosus against T. gloveri, and the field efficacy of N. longispinosus for the management of T. gloveri on adenium. The life stages of T. gloveri consist of egg, larva, protonymph, deutonymph, and adult. The inactive stages that occur between the larva and protonymph, protonymph and deutonymph, and deutonymph and adult stage were nymphochrysalis, deutochrysalis, and teliochrysalis, respectively. The total developmental duration from egg to adult lasted 7.62 days for male and 8. 71 days for female. The adult male survived for 11.30 days after emergence. The mated and unmated female lived for 14.50 and 17.10 days after emergence, respectively. The mean oviposition period for mated and unmated female was 10.70 days and 11.20 days, respectively. The average fecundity of mated and unmated female was 36.04 and 17.20 eggs, respectively. The unmated female exhibited arrhenotokous parthenogenesis, whereas mated females produced both male and female progenies in a male-to-female ratio of 1:4.7. The development of N. longispinosus recorded egg, larva, protonymph, deutonymph, and adult stages. There were no quiescent stages observed between the active stages up to adult, unlike T. gloveri. The average total development duration from egg to adult lasted 4.20 and 4.86 days, respectively, for male and female. The adult male lived for 15.00 days, whereas the adult female lived for 16.50 days on average, with an oviposition period of 12.90 days. Unmated female did not lay eggs. The female recorded a mean fecundity of 33.40 eggs with both male and female in a male-to-female ratio of 1:2.04. The study on the functional response of N. longispinosus on all life stages of T. gloveri provided evidence for a Type-II response, with no indication of a Type-III response. The present study found that N. longispinosus consumed all stages of T. gloveri and exhibited a high preference for the eggs of T. gloveri. The attack rate was observed to be highest for T. gloveri eggs (1.976), and the least was observed for adult females of T. gloveri (0.471). The predator took the longest handling time for adult T. gloveri (0.166 day) and the least for T. gloveri egg (0.055 day). The study on the numerical response of N. longispinosus to different densities of T. gloveri female showed an increase in prey consumption and oviposition, with the increase in prey density. The highest oviposition (3.05 eggs/day) was observed at a prey density of 12. The polyhouse study to evaluate the field efficacy was carried out with different predator-prey ratios of 1:25, 1:50, 1:75, 1:100, and 1:125. The study identified that the narrow predator-prey ratios of 1:25 and 1:50 were efficient in suppressing the mite population on adenium, under polyhouse conditions. During the study, a single release of the predatory mite could not suppress the prey population, so a second release of the predator was carried out. After ten days of the second release, the reduction in prey population was 94.50, 61.95, and 28.98 per cent in treatments 1:25, 1:50, and 1:75, respectively. All other treatments were found to be inferior. The control treatment recorded about a 3.36-times increase in prey population. The findings on the investigation of the biological traits, predatory potential, and field efficacy indicate that the phytosiied predator, N. longispinosus, can be an effective biocontrol agent against T. gloveri on adenium plants as an eco-friendly and sustainable alternative to synthetic acaricides. However, there is a need for continued research, for standardising technologies to scale up the mass production, as well as for field release of the predator. Studies are to be carried out to evaluate the safety of acaricides and botanicals to the predator for ensuring the successful incorporation of N. longispinosus in integrated pest management programs.The mite species has developed a significant level of resistance to commonly used synthetic acaricides, making mite management difficult in commercial horticultural nurseries. This demands the search for more viable alternative control strategies. Biological control offers a safer substitute for chemical acaricides to manage mite pests. The predatory mites of the family Phytoseiidae constitute a sizeable proportion of effective natural enemies commercially used as biocontrol agents. Among phytoseiid mite species, Neoseiulus longispinosus Evans, has been reported as a potential biocontrol agent against several spider mite species. A study was carried out in the Insectary and the Acarology Laboratory, Department of Agricultural Entomology, College of Agriculture, Vellanikkara, during the period 2022 2024 to investigate the biology of T. gloveri on adenium, the biology of N. longispinosus on T. gloveri, the predatory potential of N. longispinosus against T. gloveri, and the field efficacy of N. longispinosus for the management of T. gloveri on adenium. The life stages of T. gloveri consist of egg, larva, protonymph, deutonymph, and adult. The inactive stages that occur between the larva and protonymph, protonymph and deutonymph, and deutonymph and adult stage were nymphochrysalis, deutochrysalis, and teliochrysalis, respectively. The total developmental duration from egg to adult lasted 7.62 days for male and 8. 71 days for female. The adult male survived for 11.30 days after emergence. The mated and unmated female lived for 14.50 and 17.10 days after emergence, respectively. The mean oviposition period for mated and unmated female was 10.70 days and 11.20 days, respectively. The average fecundity of mated and unmated female was 36.04 and 17.20 eggs, respectively. The unmated female exhibited arrhenotokous parthenogenesis, whereas mated females produced both male and female progenies in a male-to-female ratio of 1:4.7. The development of N. longispinosus recorded egg, larva, protonymph, deutonymph, and adult stages. There were no quiescent stages observed between the active stages up to adult, unlike T. gloveri. The average total development duration from egg to adult lasted 4.20 and 4.86 days, respectively, for male and female. The adult male lived for 15.00 days, whereas the adult female lived for 16.50 days on average, with an oviposition period of 12.90 days. Unmated female did not lay eggs. The female recorded a mean fecundity of 33.40 eggs with both male and female in a male-to-female ratio of 1:2.04. The study on the functional response of N. longispinosus on all life stages of T. gloveri provided evidence for a Type-II response, with no indication of a Type-III response. The present study found that N. longispinosus consumed all stages of T. gloveri and exhibited a high preference for the eggs of T. gloveri. The attack rate was observed to be highest for T. gloveri eggs (1.976), and the least was observed for adult females of T. gloveri (0.471). The predator took the longest handling time for adult T. gloveri (0.166 day) and the least for T. gloveri egg (0.055 day). The study on the numerical response of N. longispinosus to different densities of T. gloveri female showed an increase in prey consumption and oviposition, with the increase in prey density. The highest oviposition (3.05 eggs/day) was observed at a prey density of 12. The polyhouse study to evaluate the field efficacy was carried out with different predator-prey ratios of 1:25, 1:50, 1:75, 1:100, and 1:125. The study identified that the narrow predator-prey ratios of 1:25 and 1:50 were efficient in suppressing the mite population on adenium, under polyhouse conditions. During the study, a single release of the predatory mite could not suppress the prey population, so a second release of the predator was carried out. After ten days of the second release, the reduction in prey population was 94.50, 61.95, and 28.98 per cent in treatments 1:25, 1:50, and 1:75, respectively. All other treatments were found to be inferior. The control treatment recorded about a 3.36-times increase in prey population. The findings on the investigation of the biological traits, predatory potential, and field efficacy indicate that the phytosiied predator, N. longispinosus, can be an effective biocontrol agent against T. gloveri on adenium plants as an eco-friendly and sustainable alternative to synthetic acaricides. However, there is a need for continued research, for standardising technologies to scale up the mass production, as well as for field release of the predator. Studies are to be carried out to evaluate the safety of acaricides and botanicals to the predator for ensuring the successful incorporation of N. longispinosus in integrated pest management programs.