The spider mite,Tetranychus macferlani(Baker and Pritchard) (Acari: Tetranychidae) is a pest of various crops and trees with a cosmopolitan geographic range that includes the country of Bangladesh. This study was conducted to evaluate the biological control potential of the predacious mite,Neoseiulus womersleyi(Schicha) (Acari: Phytoseiidae), againstT. macferlani. The consumption rate (when offered egg, larvae, protonymph, and deutonymph as prey) and functional responses (over different prey densities) ofN. womersleyiwere investigated in laboratory experiments. Experimental results showed that the predator consumed significantly more larvae than other stages ofT. macfarlanei. Logistic regression indicated that the predator exhibited a Type II functional response on all immature stages of prey; the number of prey consumed increased with prey density up to a maximum after which it slowly decreased. The attack rate (a) and handling time (Th) coefficients of a Type II response were estimated by fitting Holling’s disc equation to the data. The lowest estimated value ofaand the highest value ofTh were obtained for the predator feeding on deutonymphs. The lowest value ofTh was obtained for the predator feeding on larvae. However, the attack rate on larvae was not significantly different than the attack rate obtained on eggs and protonymphs. The predicted maximum daily prey consumption was 212.8 eggs, 238.1 larvae, 53.5 protonymphs, and 29.6 deutonymphs. Thus, our results suggest thatN. womersleyicould be a highly efficient biological control agent ofT. macfarlaneiat least at low prey densities, although field studies are needed to draw firm conclusions.
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Phytophagous mites are becoming more aggressive as pests on vegetable crops due to environmental changes and cropping systems. In general, tetranychid mites are harmful and widespread pests on numerous crops and ornamental plants (Kasap and Atlihan 2011).
Tetranychus macfarlanei(Baker and Pritchard) (Acari: Tetranychidae) is one of the most common spider mite pests of vegetables, fruits, forests, and ornamental plants in the world. It attacks crops of the family of Convolvulaceae, Cucurbitacae, Fabacae, Malvacae and Solanaceae (Jeppson et al. 1975), which includes bananas, beans, cotton, cucumber, eggplant, melons, okra, papaya, peanut, watermelon, and ornamentals. It occurs in Bangladesh, India, Madagascar, Mauritius, Thailand, Japan, Taiwan, USA, Malayasia, and the Canary Islands (personal communication). In Bangladesh,T.macfarlaneiis a dominant spider mite pest that infests many important agricultural crops such as jute, bean, and cucumber, and is found throughout most of the country.
Presently, control of this mite pest depends mainly on chemical applications. However, the intensive application of miticides in combination with short life cycles and high reproductive rates has led to the evolution of resistance to miticides. Most of the recent research on biological control of tetranychids has focused on the family Phytoseiidae, due to their frequent effectiveness in maintaining prey populations at low densities (McMurtry and Croft 1997; Croft and Luh 2004; Broufas et al. 2007). The phytoseiid mite,Neoseiulus womersleyi(Schicha) (Acari: Phytoseiidae) is an important natural enemy of the Kanzawa spider mite,Tetranychus kanzawakiKishida (Acari: Tetranychidae) in tea fields (Hinomoto et al. 2011). N. womersleyiis one of the most important predators of spider mites of the genus Tetranychus in Japan (Maeda and Hinomoto 2006). It was reported that N. womersleyi suppressed populations of dominant spider mites such asT. kanazawai andT. urticaeKoch at low prey densities (Mori and Saito 1979; Hamamura 1986). N. womerslyialso suppressed a dominant spider mite,T. macfarlanei, in Bangladesh (personal observation), but no detailed information is available on predator-prey interactions.
The functional response concept was first described by Holling (1959) and has been widely utilized to evaluate effectiveness of predators (Laing and Osborn 1974; Everson 1980; Sabelis 1985; Trexler et al. 1988; De Clercq et al. 2000; Badii et al. 2004; Reis et al. 2003, 2007; Timms et al. 2008). The rate at which predators attack prey is to some extent dependent on prey density. This relationship has been defined as the functional response (Solomon 1949). It is one of the most important aspects of a predator-prey relationship and a major parameter of population models (Berryman 1992). It has been used to predict mechanisms underlying predator-prey dynamics and to predict the potential effectivness of candidates for biological control (Sepúlveda and Carrillo 2008). The functional response can determine if a predator is able to regulate the density of its prey (Murdoch and Oaten 1975), i.e., it must show density dependence; the predator must respond to higher prey densities by consuming an increasing proportion of the available prey over a range of prey densities (Schenk and Bacher 2002).
Despite the potential ofN. womersleyifor tetranychid control, no information is available about its predator-prey interactions with T. macfarlanei. This information is essential to predict the efficiency of N. womersleyias a biological control agent of spider mites, and in particular for tetranychid mites. The present study was designed to compare the consumption rate and functional responses of N. womersleyi feeding on different stages of T. macfarlanei. The following questions were addressed: (i) does the feeding rate of the predator vary among different stages of same prey species?; (ii) are functional responses different among different stages of the same prey?; (iii) what is the potential of this predator for biological control ofT. macfarlaneipopulations?
Materials and Methods
Stock cultures of mites
The stock culture of N. womersleyi was maintained using all stages ofT. urticaeon common bean leaves,Phaseolus vulgarisL. (Fabales: Fabaceae), in a rearing chamber (25 ± 2 °C, 65 ± 10% RH and 16:8 L:D). Leaves were placed upside-down on a layer of filter paper placed on a polystyrene pad (2 cm thick) saturated with tap water. This set-up was placed in a plastic box (20.9 15 9.5 cm) to which water was added daily to keep the filter paper and polystyrene pad wet, and to cover the base of the box to prevent the mites from escaping. A surplus of all stages of
T. urticaewas brushed daily onto the leaf by using a soft brush and funnel. Leaf discs were renewed as necessary. The predatory mites used in the experiment were reared for at least three consecutive generations prior to this study. The spider miteT. macfarlaneiwas cultured on leaf discs (~ 12 cm2) of P. vulgaris placed on a water-saturated polyurethane mat in a Petri dish (9 cm diameter) at 25 ± 2 °C under a 16:8 L:D photoperiod (Gotoh et al. 2006).
All experiments were carried out at 25 ± 1 °C, 65 ± 10% RH and 16:8 L:D photoperiod. Reproductively active females of N. womersleyi were used in all experiments. Before each test, the predators were placed individually in Petri dish (9 cm diameter) and starved for 24 hours. The leaf discs were surrounded with strips of wet filter paper in order to minimize the escape of individual mites. Individuals trapped in the wet filter paper surrounding the leaf discs were excluded from data analysis.
To assess consumption rates on different life stages, 100 newly emerged individual eggs, larvae, protonymphs, and deutonymphs ofT. macfarlaneiwere offered as food. After 24 hours, the number of individuals consumed was recorded by counting intact or living prey stages (Gotoh et al. 2004b). 15 to 20 replicates were conducted for each prey life stage.
Functional response experiments were also carried out in Petri dishes with a leaf arena of 4 cm2. Once again, reproductively active, gravid females were used. The experiments were conducted with seven densities (5, 10, 20, 40, 50, 70, and 100 newly-emerged individuals) of different prey stages (egg, larvae, protonymph, and deutonymph). Prey mites were transferred onto leaf discs with a fine soft brush and then a single predator (starved for 24 hours) was released into the dish. After 24 hours, the predators were removed and the number of consumed or/and killed prey was counted. Individuals injured during transfer were excluded from analysis. After 24 hours, the number of prey items consumed was recorded by counting intact or living prey that remained. For each prey life stage 15 to 20 replicates were conducted.