In this study, the effect of temperature on the development and reproduction of T. (T.) setubali was studied at 15, 20, 25, 30 and 35 °C with 65 ± 5 % RH and photoperiod of 16:8 (L:D)h when feeding on instars of Panonychus ulmi (Koch) and Tetranychus urticae (Koch) (Acari: Tetranychidae), and pollen of Typha latifolia L. (Typhaceae). Overall, the optimal development and reproduction were observed at 30 °C on P. ulmi, the shortest developmental times for both sexes were 6.02 d for female and 5.13 d for male. Lower developmental thresholds (tmin) from egg to adult stage were higher on pollen than on prey and adults needed more degree days when fed on T. urticae. Also, optimal fecundity, rm, and R0 were recorded at 30 °C on P. ulmi (25.9 eggs/ female, 0.205 d-1, and 14.5 offspring/individual, respectively). Considering these results, T. (T.) setubali develops and reproduces better at high temperatures feeding on P. ulmi and can be released as a biological control agent against Tetranychid mites in the warm areas. Further laboratory-based studies are needed to draw biological conclusions.
Keywords: Phytoseiidae, Development, Temperature, Life table, Feed diet
Typhlodromus (Typhlodromus) setubali is a predatory mite belonging to the family Phytoseiidae. This phytoseiid was observed in many countries of the Mediterranean basin on Olea europea, Cupressus sp, and Cynodon dactylon McMurtry and Bounfour (1989) as well as on the vine Tixier et al., (2003). In Morocco, the investigations conducted in 2002 and 2003 succeeded to describe five new species and improved the old description of two species, T. (T.) setubali and T. (A.) clairathiasae Tixier et al., (2016).
Typhlodromus (T.) setubali was morphologically confused with T. (T.) moroccoensis Denmark (1992). Both species present a taxonomic similarity in the genus Typhlodromus (Typhlodromus) by the presence of six setae on the Genu II Chant and Yoshida-Shaul (1987). For overcoming this confusion, the new chaetotaxy and adenotaxy measurements for both sexes of T. (T.) setubali are now available.
Lacking bibliographic information on the development and reproduction of T. (T.) setubali constitutes a real limit to assess our result with the necessary confidence. In this study, we tried to establish some biological features of this predatory mite on three food diets at five constant temperatures chosen for objective reasons related to the local climatic conditions. However, the temperatures of 15 and 20 °C represent the averages recorded between February and March at the beginning of the growing season, 25 °C is approximately the average of temperatures reigning during April and May, whereas 30 °C and 35 °C correspond to the levels occurring between July and November when diapausing females move to the anfractuosities.
Three food diets were tested in this study, two immature instars of Panonychus ulmi (Koch) and Tetranychus urticae (Koch) (Acari: Tetranychidae). The third food diet was the cattail pollen of Typha latifolia L. (Typhaceae), a standard natural food for predatory mites Park et al., (2011), imported from the biological center for population management, SupAgro Montpellier, France.
MATERIALS AND METHODS
Rearing of mites
Panonychus ulmi and T. urticae were collected from the apple tree, Malus domestica Borkh, cv. Jeromine (Rosaceae), Oulmes, Morocco (33 ° 26 ' 19.6 " N, 5 ° 58 '35.7 " W) and reared separately on the green bean plants Phaseolus vulgaris L. (Leguminosae), in a growth chamber under the ambient conditions of summer for four generations before the beginning of experiments.
The initial population of predator was obtained from Riyad-Fruit orchard, Tiddas, Morocco (33 ° 33' 37.0 " N, 6 ° 15' 40.8 " W). Specimens were collected on the apple tree, Malus pumila Mill. cv. Anna (Rosaceae) and reared separately in arenas under controlled conditions (25 ± 1 ° C, 65 ± 5 % RH, and photoperiod of 16 L: 8 D for four successive generations before the starting of experiments. The rearing units consist of black plastic tiles surrounded by wet Kleenex tissue to avoid the escape of mites and desired humidity was maintained with water. Each rearing unit received one food, to prevent contamination of the original strains. Typhlodromus (T.) setubali was held and periodically fed by adding infested green bean leaflets, whereas the pollen of T. latifolia L. (Typhaceae) was providing to predators daily in a quantity of 0.5 mg. Stock colonies of predators were obtained from each rearing unit for use in the experiments.
Development and longevity of T. (T.) setubali
To determine the developmental time of each life stage of T. (T.) setubali and population parameters, adult females of predator were randomly taken from the rearing units and transferred to infested been leaves to lay eggs. After 24h, females were removed and each egg was transferred using a ﬁne brush to a bean-leaf disc (3 cm diameter) with one food diet. A total number from 50 to 60 eggs was once maintained and laboratory experiments were starting with twelve replications for each treatment. The leaf discs were placed on a wet cotton pad in a Petri dishes (9 cm diameter), which kept inside a growth chamber set to one of five constant temperatures, 15, 20, 25, 30 and 35 °C, 65 ± 5 % RH and 16:8 (L:D) as photoperiod. The withered leaf discs were changing every three days and predatory mites were transferring to fresh discs with the assigned food.
After hatching, the first instars received daily a total of 20 immatures of each prey and 0.5 mg of pollen with a fine paintbrush every 24 hours. Predators were observed daily during experiments. Survival and development time from egg to adult stage of predator were recorded on each food diet at the range of temperatures tested.
Life table parameters
To determine the life table parameters of T. (T.) setubali, an adult male, was randomly taken from the arena units, where predators had obtained on each food diet and introduced using a ﬁne brush to leaf disc containing a newly emerged female. Males were removed after copulation was observed in each leaf disc. Subsequently, the newly emerged mated females were followed daily. The oviposition, fecundity, and longevity were recorded and analysed for determining the response of T. (T.) setubali when fed on various food diets and exposed to a range of temperatures from 15 to 35 °C.
Life history data of both sexes of predators were analyzed according to the age-stage, two-sex life table Chi and Liu (1985) and the method described by Chi (1988). The standard errors of the population parameters were estimated by using the bootstrap method Efron and Tibshirani (1993).
The survival rates of predators were compared by using the χ2 test and the effect of food diet on the development and reproduction of T. (T.) setubali with temperature as covariable was analyzed using analysis of covariance (ANCOVA). When a Shapiro-Wilk test indicated that data were normally distributed, the pairwise comparisons among diets were analyzed using Levene test (F). When data were not normally distributed, a nonparametric Kruskal-Wallis test (K) was used. Means were compared by using the Dunn / bilateral test procedure and the Tukey-Kramer honestly significant difference (HSD) test. In all tests, P-values smaller than or equal to 0.05 were considered significant (Sokal and Rohlf 1994).
Temperature-dependent developmental rates of stages of T. (T.) setubali fed on three food diets were determined by the temperature summation model and estimated by using the reciprocal of the average days (1/d) of its duration Campbell et al., (1974). The relationship between developmental rate (1/d) and temperature (T) was estimated by the linear model.
All statistical analyses were performed using R Commander, a graphical user interface in conjunction with R program ver. 3.5.3. R Core Team (2019).
Survival and development
Survivorship of T. (T.) setubali was higher at the range of temperatures tested. At a 5 % level of significance, the χ2 test statistic did not reject the null hypothesis of equality of survivals among the different temperatures at each food source, yielding a P-value from 15 to 35 °C equal to 0.987 (χ2 = 9.978) and 0.997 (χ2 = 8.005), respectively. Moreover, no significant differences were found in the survivorship of predators among the three food sources with most of the temperatures tested (Table 1).
The mean developmental time of each stage of the predator is given in Table 2. The time required for eggs to hatch (incubation period) ranged from 7.05, 6.71, and 6.75 days at 15 °C to 1.36, 1.38, and 1.40 days at 35 °C when T. (T.) setubali fed on T. latifolia pollen, P. ulmi, and T. urticae, respectively. The developmental times of larvae, protonymphs, and deutonymphs were slightly longer on pollen than on T. urticae and P. ulmi at 15 °C and 20 °C (Table 2). For both sexes, total immature developmental time of T. (T.) setubali decreased as temperature increased from 15 to 30 °C whatever the food diet, the longest time was significantly observed on cattail pollen at 15 °C (25.33 days for females and 24.25 days for males), whereas the shortest developmental period was recorded at 30 °C when predator fed on P. ulmi (6.02 days for female and 5.13 days for male.
The ANCOVA results showed that there was a significant effect of temperature and food diet on the developmental time of predator, except for predators feeding on T. latifolia pollen, for which, the total development time from larva to deutonymphs was not influenced by temperature changes (F = 8.096, R2 = 0.73, P = 0.065) (Table 2). Overall, the significant differences were observed among the food diets tested. Development time of eggs was similar on both prey and pollen items at 35 °C (K = 0.808, P = 0.668). For larvae and protonymphs, no difference between the developmental periods was observed at 15 °C (F = 3.215, P = 0.053 and F = 0.820, P = 0.449, respectively) and 30 °C (F = 2.600, P = 0.089 and F = 1.101, P = 0.344, respectively). For deutonymphs, the statistical test showed the same trend at 25 °C (F = 1.662, P = 0.205), whereas the developmental time for females was similar on prey and pollen at 30 °C and 35 °C (F = 0.054, P = 0.947 and F = 0.962, P = 0.392, respectively). Finally, no effect of food diets on the development of adult males was observed at 20 and 35 °C (K = 4.388, P = 0.111 and K = 2.277, P = 0.320, respectively) (Table 2).
The relationship between the development and temperature was described with the linear developmental model and the estimated parameters are displayed in Table 3. The results showed that the lower developmental threshold (tmin) changes from one stage to another depending on the food types. However, the lower values of tmin of females and males were observed when predatory mite fed on P. ulmi immatures than on T. latifolia pollen or T. urticae, on which, the development of both sexes of predator required more degree-days feeding comparing to remaining food diets (Table 3), while more degree-days are needed for immature stages develop on T. latifolia than on prey. However, from egg to adult, T. (T.) setubali required a thermal budget of approximately the same day-degrees above the low developmental threshold for females (154.65 and 156.12 cattail pollen and T. urticae, respectively) or males (143.70 and 147.27 cattail pollen and T. urticae, respectively).
Longevity and oviposition
Results of the reproduction parameters of T. (T.) setubali are presented in Table 4. Overall, both temperature and food diet influenced significantly the reproduction parameters, especially, the oviposition period, longevity, and daily fecundity, but not the total fecundity and sex ration (P > 0.05). However, no significant difference among the food diets tested, which lead to similar values of preoviposition and postoviposition at all temperatures, except for 25 °C (K = 25.616, P < 0.0001 and K = 14.945, P = 0.001, respectively). In the same way, the oviposition period of predator females feeding on prey and pollen items was similar at temperature ranged from 15 to 30 °C with the alone except when the temperature rises to 35 °C (K = 8.270, P = 0.016). On another side, predator females had a different oviposition activity, females tend only to lay a similar total number of eggs at 20 °C (F = 0.411, P = 0.666) with similar daily number at 15 and 20 °C (K = 2.910, P = 0.233 and K = 0.001, P = 0.999) (Table 4).
The longevity of predator females decreased from 67.10, 63.31 and 64.79 days, at 15 °C to 18.01, 15.80 and 16.10 days at 35 °C, when feeding on cattail pollen, P. ulmi and T. urticae immatures, respectively (Table 4). The highest fecundity of T. (T.) setubali females was recorded at 30 °C when the predator fed on P. ulmi (25.89 egg/ female), with an average daily fecundity of 2.05 eggs/female/day, whereas, the lowest was observed on pollen (12.17 eggs/ female), with an average of 1.02 eggs/ female/day.
Subsequently, both the food diet and temperature did not significantly influence the sexual dimorphism of predator progeny. Whether on prey or pollen, the sex ratio takes similar values at temperatures from 15 to 30 °C, but a significant difference among food diets was observed at 35 °C (K = 17.663, P = 0.0001). However, the offspring was strongly male at low temperatures from 15 to 20 °C, whatever the food diet, whereas, the progeny had the highest female-biased sex ratio when T. (T.) setubali fed on P. ulmi and T. urticae immatures than the progeny of predators consuming T. latifolia pollen (78, 73 and 63 %, respectively) (Table 4).
Life tables parameters
No significant difference was observed between the net reproduction rates obtained when females fed on T. latifolia, P. ulmi and on T. urticae (F = 0.736, R2 = 0.19, P = 0.454; F = 1.433, R2 = 0.32, P = 0.316 and F = 1.256, R2 = 0.29, P = 0.344, respectively) (Table 5). Overall, the temperature influenced significantly the predator growth but no significant difference was observed between life table parameters whatever the food diet as justified by statistical tests (Table 5).
In parallel with the trend observed for immature and adult stages, a dropping trend in the mean generation time was observed from 15 to 35 °C. The intrinsic rate of increase, finite rate of increase, and the net reproduction rate increased significantly from 15 to 30 °C with a slight decrease at 35 °C whatever the food diet. The lowest values of rm, R0, λ, and T were obtained on pollen than on prey at the range of temperatures tested. The intrinsic rate of increase rm and the net reproduction rate R0 were higher at 30 °C on prey, especially when T. (T.) setubali fed on P. ulmi (0.20 d-1 and 14.49 offspring/ individual, respectively). For the mean generation time (T), it decreased significantly with increasing temperature on prey and pollen items, the shortest mean generation time was 11.24 d on P. ulmi at 35 °C (Table 5).
This is the first study on the biology of the predatory mite, T. (T.) setubali. According to the results, this predator can successfully develop, over a range of temperatures from 15 to 35 °C on prey and pollen, suggesting that T. (T.) setubali is a generalist predator. Survivorship of predators was lower on pollen than on prey and similar results have been reported for other species of Phytoseiids (Eveleigh and Chant, 1981; Croft and Croft, 1993; Davidson et al., 2016; Liu and Zhang, 2017). The survival rate of T. (T.) setubali was not significantly affected by the food diet (Table 1). The development periods recorded increased as temperature increased up to 30 °C, with a slight decrease at 35 °C (Table 2). Typhlodromus (T.) setubali has a shorter development time and higher reproductive activity at 30 °C when fed on immature stages of P. ulmi and T. urticae than on pollen. Also, males completed their development faster than females whatever the temperature and food diet. Therefore, it is considered to be advantageous for successful mating and increasing the population Gotoh et al., (2004).
The linear equations estimated tmin to be lower for both sexes of T. (T.) setubali feeding on Tetranychid prey than on pollen of T. latifolia, especially, for females than males when feeding on P. ulmi immatures. This may be related to the ability of females to overwinter in reproductive diapause coincided therefore to their enhancement to withstand lower temperatures (Veerman 1992; Coleman et al., 2014).
An Intensive oviposition activity of females was observed between 25 and 30 °C when fed on prey than on pollen. In addition to the developmental data, for the fecundity rate and the demographic parameters, it seems that 30 °C is also the optimal temperature for the reproduction of T. (T.) setubali. Although the highest oviposition period was observed when females fed on T. urticae between 20 and 25 °C, the daily and total fecundity in predator females was higher on P. ulmi, which seems to be a more appropriate prey of this species. Moreover, the development time to reach reproductive age is reduced in comparison with that observed on T. urticae and T. latifolia pollen.
According to the data described, food had a significant effect on the development of T. (T.) setubali, except for the protonymphs at 25 °C and 30 °C, with females and males at 35 °C (Table 2). Probably, the stage of protonymph is not mainly affected by qualitative but quantitative characteristics of food as the nutritious and energetic value of food may be more important in reaching adulthood. Similar results have been recorded in several phytoseiid species such as Typhlodromus phialatus Athias-Henriot and Euseius stipulatus Athias-Henriot (Ferragut et al. 1987), Typhlodromus athenas Swirski and Ragusa Kolokytha et al., (2011) and Typhlodromus talbii Athias-Henriot Camporese and Duso (1995).
The previously published results showed that predator mites can develop and reproduce on a wide variety of food diets (Zhang et al., 1999; Lorenzon et al., 2012; Goleva and Zebitz, 2013; McMurtry et al., 2013; Tsolakis et al., 2016). Although the results obtained under the controlled conditions do not represent perfectly the populations at the scale of the ecosystems Van Rijn and Tanigoshi (1999) and were only indicative of the effective capacity of the predators Janssen and Sabelis (1992), we can conclude that T. (T.) setubali develops and reproduces effectively on Tetranychid mites and can also be maintained on pollen. For most predators of the family Phytoseiidae, optimal development and reproduction have recorded when fed on prey whatever the experimental conditions. Typhlodromus (T.) setubali appears to be a generalist predator Type III (McMurtry and Croft, 1997; McMurtry et al., 2013). Laboratory-based studies are needed for determining the functional and numerical responses related to this species.
Temperature and food diet influenced the development and reproduction of T. (T.) setubali. For temperatures between 30 and 35 °C, coinciding with the mean temperatures recorded during summer in Morocco, this species has higher developmental rates on prey than on pollen, with higher intrinsic rates of increase. The predatory mite T. (T.) setubali is practically able to control the phytophagous mites during the growing season and can be released as an effective biocontrol control agent.
Life tables of T. (T.) setubali provide a complementary knowledge for use in the biological control against phytophagous mites. Our results showed that the pollen of T. latifolia might be an alternative food diet for this species in the absence of suitable food.
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