Some factors affecting the development, survival and prey consumption of Neoseiulus cucumeris (Acari: Phytoseiidae) feeding on Tetranychus urticae eggs (Acari: Tetranychidae) Author(s): Guang-Yun Li & Zhi-Qiang Zhang Source: Systematic and Applied Acarology, 21(5):555-566. Published By: Systematic and Applied Acarology Society URL: http://www.bioone.org/doi/full/10.11158/saa.21.5.1
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Systematic & Applied Acarology 21(5): 555–566 (2016) http://doi.org/10.11158/saa.21.5.1
ISSN 1362-1971 (print) ISSN 2056-6069 (online)
Article
Some factors affecting the development, survival and prey consumption of Neoseiulus cucumeris (Acari: Phytoseiidae) feeding on Tetranychus urticae eggs (Acari: Tetranychidae) GUANG-YUN LI1 & ZHI-QIANG ZHANG*1, 2 1
Centre for Biodiversity & Biosecurity, School of Biological Sciences, University of Auckland, Auckland, New Zealand. E-mail:
[email protected] 2 Landcare Research, 231 Morrin Road, Auckland, New Zealand. E-mail:
[email protected] * Corresponding author
Abstract Biological control of Tetranychus urticae relies mainly on specialist predators that are capable of coping with the dense web of spider mites. The role of generalist predators, however, has been less studied. To evaluate the development and predation of immature Neoseiulus cucumeris on Tetranychus urticae eggs, three experiments were conducted in the laboratory at 25 °C. The results showed that only 20–25% N. cucumeris eggs developed into adults when provided with 120 frozen spider mite eggs at the start of the experiment. The rate of predation by predator immatures and their survival increased with prey density. When N. cucumeris were fed 12–24 frozen spider mite eggs every day from larvae, they completed their immature development in 11–14 days and consumed 133–208 spider mite eggs. When the predator was offered 200 fresh spider mite eggs at the start of the experiment, they developed faster when fed every day, with adults emerging in 7 days. It was found that the webbing of spider mite lowered the predation of N. cucumeris. Compared with specialist predators, predation rates by N. cucumeris were much higher. The potential for N. cucumeris to control of T. urticae is discussed.
Key words: Neoseiulus cucumeris, Tetranychus urticae, development, predation, biological control
Introduction The two-spotted spidermite Tetranychus urticae Koch (Acari: Tetranychidae) is a polyphagous herbivore whose hosts include many economically important crops worldwide (Zhang 2003; Van Leeuwen et al. 2010). When the plants are infested by spider mites, their leaves become yellowish and curled, resulting in lower photosynthesis and decreased yield (Klamkowski et al. 2006; Park & Lee 2005). In many cases, T. urticae is primarily controlled in crops by applying pesticides (GarcíaMarí & González-Zamora, 1999). However, T. urticae has relatively short generation time and high reproductive capacity and thus can quickly develop resistance when subject to increasingly intensive application of pesticides and acaricides (Grbić et al. 2011). With growing problems resulting from the use of pesticides, such as risks to non-targeted organisms, environmental pollution, and human health problems caused by pesticide residues (Deedat 1994), biological control is receiving increasing attention (van den Bosch et al.1982). Biological control of spider mites is practised by releasing natural enemies such as Neoseiulus cucumeris (Esterbrook et al. 2001), Phytoseiulus persimilis, Neoseiulus californicus, Feltiella acarisuga, Stethorus punctillum,and Scolothrips longicornis Priesner, and by applying pathogenic bacteria and fungi (Attia et al. 2013). Among these natural enemies, mites of the Phytoseiidae are used most often. Many semi-field and greenhouse experiments have been conducted to evaluate the © Systematic & Applied Acarology Society
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efficiency of predatory mites in controlling spider mites (e.g. Fraulo & Liburd 2007, Abad-Moyano et al. 2010). For example, Opit et al. (2004) reported that the most reliable and successful control of T. urticae on ivy geraniums occurred when P. persimilis (a type I specialist predator according to McMurtry et al. 2013) were released at the predator: prey ratio of 1:4. In addition, Neoseiulus californicus (a type II predator according to McMurtry et al. 2013) was also proved to be an efficient biological agent against two-spotted spider mite (De Souza-Pimentel et al. 2014). Neoseiulus cucumeris, as a type III species, is known as a generalist that prefers other preys than spider mites (McMurtry et al. 2013). It is most often used to control thrips such as Frankliniella occidentalis on horticultural plants, pepper, cucumber, and tomato (Gerson & Weintraub 2007). Previous studies have also shown the capacity of N. cucumeris to control tarsonemid mites such as the broad mite Polyphagotarsonemus latus (Weintraub et al. 2003) and cyclamen mite Phytonemus pallidus (Croft 1998). Due to its inability to cope with the dense spider mite webbing, relatively little attention has been paid to its potential in controlling spider mites; however, with the widening of commercialization of N. cucumeris, it is being applied to control spider mites on cotton and fruit trees in China (Luo et al. 2014; Zhang et al. 2006). It is reported the spider mite population can be suppressed in cotton fields, even after it has reached or exceeded the economic threshold, by hanging 3000–5000 bags of N. cucumeris per hectare (Luo et al. 2014). In addition, Croft et al. (1998) showed that although specialist predators could rapidly suppress cyclamen mite and two-spotted spider mite, N. cucumeris was a better choice for long-term control because it may feed on other food such as pollen. To further understand the potential of N. cucumeris to control spider mites, more studies on the biology of this predator fed with spider mites and the effects of spider mite webbing on N. cucumeris are required. In this study, we investigated three factors, namely prey density, cannibalism and spider mite web, on the development, consumption rate, sex ratio, and body size of N. cucumeris reared with T. urticae eggs. Although N. cucumeris also fed on spider mite eggs at other active stages, we focused only on eggs because they are more vulnerable to predators than other active stages; moreover, N. cucumeris is a less efficient predator for adult spider mites because of the spiders’ webs.
Material and methods Cultures of mites Neoseiulus cucumeris was obtained from Bioforce Ltd, Karaka, Auckland, New Zealand. Stock culture was maintained in a petri dish (90 mm diameter) with bran, dry yeast, and Tyrophagus curvipenis (see Ye & Zhang (2014) for the history of the T. curvipenis culture). The petri dish was placed in a plastic box with water acting as a barrier to preventing the mites from escaping. The culture was kept in a room at 20±5°C and 45±10% humidity. A population of Tetranychus urticae mites (about three hundreds) was obtained from Bioforce Ltd, and a lab colony of spider mites was established by releasing them on clean beans (Phaseolus vulgaris) in their two-leaf stages. The potted beans (3–5 plants in each pot) were replaced weekly by clean and young bean at their two-leaf stage. The plants were grown in a greenhouse with a natural photoperiod. In order to harvest T. urticae eggs, bean leaves were picked from the lab colony. The eggs were then collected from the leaf using a fine hair brush. For experiments 1 and 2 the eggs were frozen at –20°C for 12 h to prevent hatching.
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Experimental arenas The rearing cells were set up by using plexiglass slides and metal clips according to Ye & Zhang (2014). Cells used in experiment 1 and 2 were cone shaped with top diameter 6 mm and bottom diameter 3 mm in plexiglass slides (25 mm wide, 38 mm long, 3 mm thick), while the rearing units for experiment 2 were added with a small piece of moist filter-paper, which helped maintain humidity in the cell as well as provide water to the predatory mite. Rearing arenas for experiment 3 were similar to those in experiments 1–2 but the cells were larger (15 mm diameters cylinder-shaped cell)—their bottom was covered with detached bean leaf discs while the top part was covered with a piece of transparent film punctured with insect pins to allow ventilation and maintenance of humidity. Experiments All experiments were conducted in a room at 25±1°C, RH 45±10%, and a 12: 12h (L: D) photoperiod. Experiment 1: To investigate the rate of development of N. cucumeris and cannibalism, two groups of rearing cells were set up. In the first group, one predator egg less than 24 h old was added to a cell with spider mite eggs at an initial density of 2, 4, 8, 12, 16, 20, 24, 28, 32, 48, 64, 80, or 120. In the second treatment, two predator eggs were placed in a cell with the same prey densities as treatment 1. Each treatment was replicated ten times. The developmental stage of the predator mites and the number of uneaten prey eggs left in each cell were recorded every day until either the death or maturity of the predatory mite. Experiment 2: In this experiment, new frozen prey eggs were provided to predator mites every day. N. cucumeris larvae hatched within 12 h were transferred into each rearing cell with 12, 16, 20 or 24 spider mite eggs. Each treatment was replicated nine times. The developmental stage of each predator mite and the number of prey eggs consumed were checked every 24 h. Each predator was then transferred to a new cell with the same density of prey. The newly emerged adults were mounted on microscope slides in Hoyer's medium and dried at the temperature of 50°C for one week. The slides were examined with a Nikon E-800 microscope to determine the sex of the mite. The length and width of the dorsal shield of predator mites that survived to adulthood were also measured to represent body size. Experiment 3: Three types of rearing units with or without webbing/leaf (Tables 6 & 7) were prepared before one larva of predator mite was transferred into each rearing cell. The webbing was constructed by introducing 20 female spider mites into the cell for 24 h. The female spider mites were then removed carefully so the spider mite webbing was not destroyed. In this experiment, 200 fresh spider mite eggs (not frozen) were used to feed the predators either on a plastic surface or leaf surface with/without webbing. The experiment started by placing one newly emerged larva (hatched within 12 h) into each cell since it is reported larva can moult to protonymphs without feeing on any food (Zhang & Croft 1994, Schausberger & Croft, 1999). The development of the predatory mite and the number of T. urticae consumed were recorded every day. The newly hatched spider mite eggs were monitored and replaced by eggs at 12-h intervals during the experiment, but the eaten eggs were not replaced. Statistical analysis In experiment 1, the survival rates of predator mites were analysed by chi-square test. Two-way ANOVA were conducted to test the influence of prey density and conspecifics on the developmental period, survival time, and predation of protonymph predators.
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In experiment 2, the life-history parameters and total predation of each life stage was analysed by one-way ANOVA. Relationship of immature duration, total predation, and dorsal shield size with prey density were analysed by covariance analysis. In experiment 3, analysis of variance (one-way ANOVA) was used to compare developmental stage of N. cucumeris: egg to larva stage, protonymph, deutonymph, immature stage. The means were compared using LSD tests at the significant level of 0.05. All the data were analysed by using IBM SPSS for windows version 22.0.
Results Experiment 1 Immature survival. Prey and predator density both affected the survival of the different juvenile life stages of N. cucumeris (Tables 1 & 2). Both prey density and predator density did not affect the survivorships of non-feeding larvae (Chi-square test; χ2=1.22, df =12, P=0.263; χ2=3.24, df =1, P= 0.072, respectively; Table 1). Survival rates of protonymphs and deutonymphs, however, increased with the prey density from 2 eggs to120 eggs per cell (Chi-square test, χ2=2.99, df =12, P
