Different Biological Aspects of the Predaceous Mite Euseius scutalis (Acari: Gamasida: Phytoseiidae) and the Effects due to Feeding on Three Tetranychid Mite Species in Hail, Saudi Arabia

RESULTS

As in other phytoseiid mite species, both sexes passed through an egg, larva, protonymph and deutonymph before reaching adulthood. Under experiment conditions as shown in Table 1, the incubation period ranged from 1.6 to 2.0 days for both sexes. Concerning duration time of immature of E. scutalis, larval stage lasted 1.2; 1.0 and 1.54 days when it was provided with immature of T. urticae, E. orientalis and O. afrasiaticus, respectively. The same trend was observed for predator protonymph, where it lasted an average of 2.34, 2.61 and 2.78 days, while the deutonymph lasted 2.68, 2.56 and 2.74 days when they were fed on the same aforementioned preys, respectively. Therefore, the earlier results showed that the developmental time of E. scutalis wasn't significantly affected by food source and lasted 8.02, 8.19 and 9.06 days when predator immature stages of females were subjected to immature of T. urticae, E. orientalis and O. afrasiaticus, respectively (Table 1). Whatever the prey mite species, data showed that males of the predatory mite E. scutalis emerged earlier than females. In all cases, it was noticed that immature stages of T. urticae accelerated the development more than E. orientalis, while immature O. afrasiaticus were not as preferable food source as the other two species. Adulthood of E. scutalis showed that males lived for shorter time than females. Males fed on immature T. urticae, E. orientalis and O. afrasiaticus lived for 23.64, 18.80 and 16.46 days while females lived for 26.4, 22.6 and 19.4 days, respectively (Table 1). From the earlier results, it can be noticed that T. urticae prolonged the longevity of predator followed by E. orientalis and O. afrasiaticus. During oviposition period, female mite lived for 18.60 days and laid an average of 30.66 eggs with a daily rate of 1.64 eggs, while it lived for 16.40 and 14.6 days and laid 19.25 and 14.60 eggs with an average of 1.17 and 1.11 eggs day^-1 when female predator preyed on immature stages of T. urticae, E. orientalis and O. afrasiaticus, respectively (Table 2). Therefore, feeding on T. urticae significantly prolonged predator longevity and caused a higher rate of fertility (egg production).

Table 1:	Developmental time of immature stages, adult longevity and sex ratio of Euseius scutalis fed on Tetranychus urticae, Eutetranychus orientalis and Oligonychus afrasiaticus at 26°C and 70% RH
Values are represent as Mean±SE

Table 2:	Effect of different prey mite species on the duration of oviposition period, total and daily rate of egg production of Eueieus scutalis
Values are represent as Mean±SE

Fig. 1:	Age-specific fecundity (Mx) and survival (Lx) of Euseius scutalis fed on Tetranychus urticae, Eutetranychus orientalis and Oligonychus afrasiaticus. (a) Euseius scutalis fed on Tetranychus urticae immature, (b) Euseius scutalis fed on Eutetranychus orientalis immature and (c) Euseius scutalis fed on Oligonychus afrasiaticus

Concerning the effect of different prey mites on the table parameters of E. scutalis under laboratory conditions, data in Table 1 and 3 clearly showed that sex ratio was not affected by food source, where females percentages (females/females+males) averaged 58, 56 and 55% when mites were fed on immature stages of T. urticae, E. orientalis and O. afrasiaticus, respectively. These values were subsequently used in calculation the specific rate of fecundity (Mx). It was also noticed that feeding on T. urticae or E. orientalis caused a mean generation time (T) of 14.70 and 14.88 days, while T value was longer when the predatory mite was subjected to date palm red spider mite O. afrasiaticus (16.14 days), respectively. As shown in Table 2 and Fig. 1a-c, it was clear that T. urticae immature caused the highest value of net reproductive rate (Ro_{= ÓLx Mx}) of 26.73 expected female daughters per female. Feeding on immature of both E. orientalis and O. afrasiaticus resulted in lower sub-equal Ro values of 13.248 and 13.606 expected female/female, respectively. That means E. orientalis and O. afrasiaticus resulted in Ro about 50% of that obtained by feeding on T. urticae.

Table 3:	Life table parameters of Euseius scutalis fed on Tetranychus urticae, Eutetranychus orientalis and Oligonuchus afrasiaticus in lab at 26°C and 70% RH

Concerning the intrinsic rate of increase (r_m) (female/female/day), Prey mites tested here obviously affected the intrinsic rate of increase of E. scutalis where it was 0.22 female progeny/female/day when predatory mite fed T. urticae and sharply declined to 0.17 and 0.16 with E. orientalis and O. afrasiaticus, respectively (Table 3). Concerning the finite rate of increase e^rm (λ) (population multiplications in a unit of time) data showed that it was at its highest level (1.247) when E. scutalis individuals fed immature stages of T. urticae and declined to 1.192 and 1.175 after feeding E. orientalis and O. afrasiaticus, respectively.

DISCUSSION

Field observations showed that individuals of the predatory mite E. scutalis were found to feed on all stages of the two-spotted spider mite T. urticae inhabiting eggplant leaves and on citrus brown mite E. orientalis inhabiting citrus leaves as well as different scale insects and whiteflies. The previous results showed that the developmental time of E. scutalis wasn't significantly affected by food source. Similar results were obtained by Yue et al. (1994), who noticed that Euseius mesembrinus (Dean) developed in 8.5-12.5 days after feeding on different kinds of pollen grains, while Abou-Setta et al. (1997) found that Proprioseiopsis rotendus (Muma) lasted only 6.58 days when immature stages fed on T. urticae. Data also showed that males of the predatory mite E. scutalis emerged earlier than females. Similar results were obtained by Abou-Setta et al. (1997) and Mohamed et al. (2008) who reared P. rotendus and Neoseiulus cucumeris (Oudemans) on mobile stages of T. urticae and European red spider mite Panonychus ulmi (Koch), respectively. Moreover, the present results agree with those of El-Laithy and Fouly (1992), who noticed that male and female life cycle of E. scutalis averaged 6.8 and 7.8 days, respectively. Immature stages of T. urticae generally accelerated the development of predatory mite more than E. orientalis, while immature stages of O. afrasiaticus were not as preferable food source as the other two species. Similarly, Abou-Setta et al. (1997) found that immature stages of two-spotted spider mite T. urticae also accelerated the development of the phytoseiid mite P. rotendus fed different kind of food sources. However, most phytoseiid species completed their development from egg to adult female at a constant temperature of 25-26°C with a range of 5-7 days (Sherif, 1982; Abou-Setta and Childers, 1989; Caceres and Childers, 1991; Fouly and El-Laithy, 1992; Kasap and Lu, 2004; Raza et al., 2005).

Adulthood of E. scutalis showed that males lived for shorter time than females. The present results showed that T. urticae prolonged the longevity of predator followed by E. orientalis and O. afrasiaticus. Similarly, El-Laithy and Fouly (1992) found that female longevity of A. (Euseius) scutalis fed on the same prey species lasted 27.8 days, while N. cucumeris fed on P. ulmi lasted 20.15 days (Mohamed et al., 2008). Feeding on T. urticae significantly prolonged predator longevity and caused a higher rate of fertility (egg production). Similar results were obtained by Fouly and El-Laithy (1992) who found that female of A. (Neoseiulus) barkeri (Hughes) laid an average of 1.02 egg day^-1 during an oviposition period of 13 days. Moreover, Abou-Setta et al. (1997) found that T. urticae prolonged the oviposition period of the phytoseiid predatory mite P. rotendus over any kind of food sources. Therefore, it can be concluded that prolongation in oviposition period of a predatory mite may give a higher rate of egg production. Sabelis (1981) stated that the prey consumption formed a ratio of about 70% of the biomass of deposited eggs by the predatory mite. In other word, the total eggs deposited during the ovipositional period represented about 70% from total protein of consumed preys.

Survival curves (Lx) of E. scutalis fed on the previously mentioned mite preys followed a type I in which most eggs developed to maturity (92, 90 and 91%, respectively) and most female death occurred gradually after extended ovipositional period. These results agree with those obtained by El-Laithy and Fouly (1992), Abou-Setta et al. (1997), Fouly (1996) and Escudero and Ferragut (2005), who reared A. (Euseius) scutalis, A. (Typhlodromips) swirskii, Proprioseiopsis rotendus, P. asetus and Neoseiulus californicus (McGregor), respectively. Feeding on E. orientalis and O. afrasiaticus resulted in Ro about 50% of that obtained by feeding on T. urticae. El-Laithy and Fouly (1992) found that Ro of A. (Euseius) scutalis and A. (Typhlodromips) swirskii were 17.22 and 22.97. Contradictory, Escudero and Ferragut (2005) found a higher Ro value with N. californicus and P. persimilis where it reached 49.25 and 45.61 expected female progeny/female after feeding on the two-spotted spider mite T. urticae. Momen and El-Sawi (2008) found that lower Ro value was obtained when E. scutalis was provided with eggs of two Lepidopterous insects where it averaged 10.94 and 5.40 expected females/female after feeding on eggs of Spodoptera littoralis Boisduval and S. ipsillon (Hufnagel). Emmert et al. (2008) contradictory found that T. urticae was not the favorable prey mite where it caused Ro value of P. asetus 50% lower than feeding on thrips Frankkliniella occidentalis (Pergande) or cattail pollen Typha latifolia L.

Concerning the intrinsic rate of increase (r_m), Birch (1948) stated that r_m is the rate of increase of an insect species under specific physical conditions, in unlimited environment where the effects of increasing density don't need to be considered. The present study cleared that tested prey mites obviously affected the intrinsic rate of increase of E. scutalis where it was higher when predatory mite fed T. urticae and sharply declined after feeding on E. orientalis and O. afrasiaticus. Nomikou et al. (2001) reported that r_m of E. scutalis fed citrus red spider mite P. citri averaged 0.23-0.29 according to the temperature. Kasap and Lu (2004) also found that r_m value of E. scutalis fed P. citri was between 0.16 to 0.29 female/female/day by increasing temperature. While Momen and El-Sawi (2008) found that r_m value didn’t exceed 0.14 when the same predatory mite fed eggs of cotton leaf worm S. littoralis. Concerning the finite rate of increase e^rm (λ) (population multiplications in a unit of time) data showed that it was at its highest level when E. scutalis individuals fed immature of T. urticae and declined after feeding E. orientalis and O. afrasiaticus. Similar results were obtained by El-Laithy and Fouly (1992), who found that e^rm (λ) of E. scutalis fed T. urticae was 1.157, while it was only 1.106 when Momen and El-Sawi (2008) reared E. scutalis on eggs of the insect S. ipsillon. From the earlier results, it can be concluded that rearing E. scutalis on immature stages of T. urticae was considerably better than other prey mite to obtain higher values of egg production under laboratory conditions. Further experiments are highly needed to know more about different species of predatory mites as biological control agents in Saudi Arabia.