Abstract: This study aimed to determine Serangium parcesetosum preference for different prey species and parasitized Bemisia tabaci (Genn.) (Hom., Aleyrodidae) by the parasitoid, Eretmocerus mundus Mercet (Hym., Aphelinidae). The results on S. parcesetosum preference by feeding on different prey species offered separately and together indicated that the predatory larvae and adults preferred significantly the cotton whitefly, B. tabaci and the castor bean whitefly, Trialeurodes ricini (Misra) (Hom., Aleyrodidae) rather than the two-spotted spider mite, Tetranychus urticae Koch (Acari, Tetranychidae); melon aphid, Aphis gossypii Glover (Hom., Aphididae) and pea leafminer, Liriomyza huidobrensis (Blanchard) (Dip., Agromyzidae). The results on S. parcesetosum preference for the whitefly species, B. tabaci and T. ricini demonstrated that there were no significant differences in the preference of both predatory larvae and adults for any whitefly species. Moreover, S. parcesetosum larvae and adults were significantly tended to avoid parasitized puparia of B. tabaci by E. mundus and fed instead on unparasitized ones. Thus, there is a feasible potential for integration the predator and the parasitoid into a biological control program to suppress B. tabaci.
INTRODUCTION
Vegetables are one of the main crops grown in Jordan and the planted area is estimated to be around 401,700 dunums (dunum = 1000 m2) (Agricultural Statistical Book, 2005). However, there are many pest species attacking vegetable crops in Jordan. The most dangerous is the cotton whitefly, Bemisia tabaci (Genn.) (Hom., Aleyrodidae), which attacks numerous plant species and transmits many viral plant diseases (Sharaf and Hasan, 2003). In addition to this pest, the castor bean whitefly, Trialeurodes ricini (Misra) (Hom., Aleyrodidae); the two-spotted spider mite, Tetranychus urticae Koch (Acari, Tetranychidae); the melon aphid, Aphis gossypii Glover (Hom., Aphididae) and the leafminer, Liriomyza huidobrensis (Blanchard) (Dip., Agromyzidae) are locally and cosmopolitan polyphagous pests attacking many vegetable crops (Hagvar and Hofsvang, 1994; Abd-Rabou, 1999; Scheffer, 2000; Gerling et al., 2001; Aucejo et al., 2003).
Currently, all the fore-mentioned pest species are increasingly becoming more important pests, because the effectiveness of chemical pesticides applied to these pests have been dogged by the development of resistance within pest populations (Kranthi et al., 2001; Civelek and Yoldas, 2003; Sato et al., 2005). Predators and parasitoids have a key role in regulating pest populations (Necetic et al., 2001; Civelek et al., 2002; Jazzar and Hammad, 2004). However, Serangium parcesetosum Sicard (Col., Coccinellidae) is an important predator of whiteflies. It was found feeding voraciously on the woolly whitefly, Aleurothrixus floccosus Maskell (Argov, 1994); the sugarcane whitefly, Aleurolobus barodensis Mask. (Patel et al., 1996); the silverleaf whitefly, Bemisia argentifolii Bellows and Perring (Ellis et al., 2001); the citrus whitefly, Dialeurodes citri (Ashmead) (Yigit et al., 2003); as well as B. tabaci and the greenhouse whitefly, Trialeurodes vaporariorum Westwood (Al-Zyoud et al., 2005). The parasitoid, Eretmocerus mundus Mercet (Hym., Aphelinidae) has been used worldwide to control B. tabaci (Urbaneja and Stansly, 2004) and it is a native parasitoid in Jordan (Hassan, 1999), as well as its parasitism on B. tabaci accounted for 71% (Sharaf and Batta, 1996).
Concomitantly, in order to locally achieve a successful management of the previously mentioned pests, especially B. tabaci in vegetables, which has relied on insecticides and to escape of the developed resistance to insecticides by pests, it was important to check the predation ability of S. parcesetosum on these pests. Moreover, in comparison with the previous findings, this study is expected to increase the host pest spectrum of S. parcesetosum and to investigate its discrimination ability to the whiteflies’ parasitoid, E. mundus, since the later is a native and efficient parasitoid of B. tabaci in Jordan and has not been studied worldwide yet. Therefore, in the present work, the preference of S. parcesetosum for different pest species and parasitized B. tabaci by E. mundus at different temperatures were studied. All these experiments have the goal of comprehensively studying the potential of this promising predator to develop a new successful biological control possibility of stubborn pests in Jordan.
MATERIALS AND METHODS
A stock culture of S. parcesetosum was established from several individuals of the predator available at the Faculty of Agriculture, Mu’tah University. The predator’s population was built up on B. tabaci reared on cucumber plants, Cucumis sativus L. in metal meshed cages (50x50x50 cm). The cages were sealed with gauze from their sides and tops in order to provide ventilation. To maintain adequate prey supply for the predator continuously, cucumber plants infested with B. tabaci were frequently replaced inside the cages. For rearing the parasitoid, E. mundus, parasitized puparia of B. tabaci on cabbage leaves, Brassica oleracea L. were collected from open fields of Al-Waleh Valley, Jordan and brought to the laboratory. The emerged parasitoids were reared further on cabbage plants infested with B. tabaci in similar meshed cages as mentioned before. For the experiments on prey species preference by S. parcesetosum, several species of arthropods, which usually attack vegetables, were reared and tested as possible prey for the predator. These were B. tabaci, T. ricini, T. urticae, A. gossypii and L. huidobrensis. In order to establish the stock culture of B. tabaci, thousands of the insect adults were collected by aspirator from cucumber plants grown under greenhouses and were further maintained on cucumber plants. T. ricini was obtained from Balqa Applied University, Jordan and reared on castor bean plants, Ricinus communis L. The stock cultures of T. urticae, A. gossypii and L. huidobrensis were obtained on leaves collected from tomato, Lycopersicon esculentum Mill, cucumber and squash, Cucurbita pepo L. plants grown under greenhouses, respectively and maintained on cucumber plants. All stock cultures of the pest species were reared in metal meshed cages (80x50x50 cm) under laboratory conditions of 22-33°C at the Faculty of Agriculture, Mu’tah University, Jordan.
The desired stages of S. parcesetosum for the experiments were obtained in large round Plexiglas cages of 9 cm in diameter and 1.5 cm in height. Each cage was filled partially with 0.5 cm thick layer of wetted cotton pad and its lid was fitted with a meshed hole to provide suitable ventilation. Sixteen adults of S. parcesetosum females and males were transferred onto cucumber leaves with highly B. tabaci infestation in each round cage. After 24 h, the adults were removed and the laid eggs were reared further and checked daily until they reached the convenient stage. For obtaining the required stage of the whiteflies, B. tabaci and T. ricini, cucumber and castor bean plants were exposed to the insect infestation, respectively in the stock culture cages for 12 h and then incubated until reaching the convenient stage for the experiments. In order to obtain T. urticae, A. gossypii and L. huidobrensis in their appropriate stages for the experiments, the required stages from the different prey species were identified under a binocular microscope in the laboratory on leaves obtained from the different host plants in the different stock cultures and picked up gently, using a camel-hair brush. All the experiments were conducted in small round Plexiglas cages (5 cm-diameter and 1 cm-height) filled with 0.5 cm thick wetted cotton pad, in which cucumber leaf discs were placed upside down onto the wetted cotton pad. All experiments on prey species preference and parasitized prey were conducted in summer, 2006 at a constant temperature of 25±1°C and a range one of 22-33°C, in which the later one represents temperature regimes frequently encountered between April and November in Jordan, a period where the infestation by all the prey species mostly occurs, as well as relative humidity of 60±15%. All experimental groups were replicated twenty times with each predatory stage, prey species and temperature.
Multi-choice experiments were conducted to determine the predation preference by S. parcesetosum for different prey species and parasitized prey. To investigate the predator preference for different prey species, fourth larval instars (L4) or one-week-old adults of S. parcesetosum were separately kept on a cucumber leaf disc (3 cm in diameter) in the small round Plexiglas cages with ten individuals of each B. tabaci (puparia), T. ricini (puparia), T. urticae (adults), A. gossypii (1-2 days old) or L. huidobrensis (puparia) separately. The predatory individuals were transferred daily to new round cages, which contain fresh prey from the five different species separately. The number of consumed prey of each species was daily recorded. A second group of experiments was carried out to evaluate the preference of S. parcesetosum L4 instars and one-week-old adults for the same five prey species, when they were offered together in the round Plexiglas cages on a cucumber leaf disc (3 cm in diameter). Each predatory stage tested was kept with fifty individuals; ten of each B. tabaci puparia, T. ricini puparia, T. urticae adults, 1-2 days old of A. gossypii and L. huidobrensis puparia together in the round Plexiglas cages described above. The predator individuals were transferred daily to new round cages provided with fresh prey from the five different species together. The number of consumed prey of each species was daily recorded.
A third group of experiments was set up to test the predation preference of S. parcesetosum for the whiteflies; the cotton whitefly, B. tabaci and the castor bean whitefly, T. ricini. Each L4 instar or one-week-old adult of S. parcesetosum was kept with ten puparia of B. tabaci and ten puparia of T. ricini together in the round Plexiglas cages on a cucumber leaf disc of 3 cm in diameter. The predatory individuals were daily transferred to new round cages, containing fresh prey from the two species together and the number of consumed individuals of each whitefly species was recorded. A fourth group of experiments was established to record the interaction between S. parcesetosum and E. mundus. For these experiments, the puparia of B. tabaci were used after one week of parasitism by E. mundus. Ten unparasitized and 10 parasitized puparia of B. tabaci were placed together on a cucumber leaf disc (3 cm in diameter) in the round Plexiglas cages with each L4 instar or 7-day-old adult of S. parcesetosum. The puparia were arranged in rows of five puparia with unparasitized and parasitized whiteflies alternating one beneath the other in a uniform distribution in the cages. The S. parcesetosum larvae and adults were removed after 24 h and the number of consumed unparasitized and parasitized puparia was counted.
In order to affirm the basic assumptions of the data to be analysed, they were tested for the normal distribution and the homogeneity of variance using the Barlett-Test (Köhler et al., 2002). One- or two-factor-analysis of variance was conducted to detect differences among means. In case of differences among means were detected, the second step was then to determine the significant differences among the means at a probability level of 0.05. In which, among several means the LSD Test was used (Clewer and Scarisbrick, 2001), while in case of comparing between two means only, t-Test was conducted (Anonymous, 1996).
RESULTS
The results in Table 1 indicated that at both temperatures tested the predatory larvae preferred significantly the whiteflies species tested, B. tabaci and T. ricini rather than mite, T. urticae; aphid, A. gossypii and leafminer, L. huidobrensis. Also, the larvae preferred significantly the mite to aphid and leafminer. The predation rate of S. parcesetosum larvae were means of 9.25, 9.65, 1.90, 0.75 and 0.45 at 25°C as well as 9.50, 8.65,
| Table 1: | Predation rate of Serangium parcesetosum fourth larval instars by feeding on five different prey species offered separately on cucumber leaf discs at two different temperatures |
| Different capital letter(s) in columns indicate significant differences between the different temperatures within the same prey species, while different small letter(s) in rows indicate significant differences among the different prey species within the same temperature at p≤5% (Two-factor analysis of variance) | |
| Table 2: | Predation rate of Serangium parcesetosum adults by feeding on five different prey species offered separately on cucumber leaf discs at two different temperatures |
| Different capital letter(s) in columns indicate significant differences between the different temperatures within the same prey species, while different small letter(s) in rows indicate significant differences among the different prey species within the same temperature at p≤5% (Two-factor analysis of variance) | |
1.75, 0.80 and 0.40 individuals at 22-33°C from B. tabaci, T. ricini, T. urticae, A. gossypii and L. huidobrensis, respectively. In contrast, the predatory adults preferred significantly the whiteflies tested more than mite and aphid and the later two species were significantly preferred to leafminer at both temperatures (Table 2). The predatory adults at 25 and 22-33°C, respectively consumed daily means of 9.40 and 9.05 B. tabaci as well as 9.75 and 8.65 T. ricini. On the other hand, means of 1.95 and 1.65 T. urticae as well as 1.55 and 1.40 A. gossypii were consumed at 25°C and 22-33°C, respectively. However, a very little predation rate of 0.40 and 0.50 L. huidobrensis was recorded for S. parcesetosum adults at 25 and 22-33°C, respectively. Moreover, there were no significant differences in the mean daily predation rate by both larvae and adults of S. parcesetosum between the two different temperatures within the same prey species, except that one for T. ricini, in which both tested stages of the predator were significantly consumed more T. ricini at 25°C than 22-33°C (Table 1 and 2).
The predatory larvae (Table 3) at 25°C had significantly a general tendency in the prey preference toward the whitefly species used, but with greater preference for T. ricini than B. tabaci with a mean of 8.45 vs. 7.65, respectively. From the other three prey species, very few individuals were consumed, where daily means of 0.90, 0.35 and 0.05 were consumed from T. urticae, A. gossypii and L. huidobrensis, respectively. While at 22-33°C, the predatory larvae preferred significantly B. tabaci and T. ricini rather than mite, aphid and leafminer, also, with more preference to the mite than aphid and leafminer. The predation rates were means of 7.25, 7.90, 1.30, 0.40 and 0.05 individuals of B. tabaci, T. ricini, T. urticae, A. gossypii and L. huidobrensis, respectively.
| Table 3: | Predation rate of Serangium parcesetosum fourth larval instars by feeding on five different prey species offered together on cucumber leaf discs at two different temperatures |
| Different capital letter(s) in columns indicate significant differences between the different temperatures within the same prey species, while different small letter(s) in rows indicate significant differences among the different prey species within the same temperature at p≤5% (Two-factor analysis of variance) | |
| Table 4: | Predation rate of Serangium parcesetosum adults by feeding on five different prey species offered together on cucumber leaf discs at two different temperatures |
| Different capital letter(s) in columns indicate significant differences between the different temperatures within the same prey species, while different small letter(s) in rows indicate significant differences among the different prey species within the same temperature at p≤5% (Two-factor analysis of variance) | |
The predatory adults (Table 4) at both temperatures preferred significantly B. tabaci and T. ricini rather than mite and the later to aphid and leafminer. The predation rates were means of 8.75, 9.00, 1.40, 0.25 and 0.10 at 25°C as well as 7.15, 7.70, 1.35, 0.45 and 0.05 at 22-33°C from B. tabaci, T. ricini, T. urticae, A. gossypii and L. huidobrensis, respectively. In addition, the results indicated that there were no significant differences in the daily predation rate by both larvae and adults of the predator between the two different temperatures within the same prey species, except that the larvae consumed significantly more T. urticae at 22-33°C than at 25°C (Table 3) and the adults more B. tabaci and T. ricini at 25°C than at 22-33°C (Table 4).
Further statistical analysis on the data in Table 1 to 4 was conducted in order to find if there are significant differences when the 5 prey species were offered separately or together. The statistical analysis indicated that at 25°C the predatory larvae consumed significantly more individuals from all prey species when they offered separately rather than together. While the predatory adults consumed significantly more from the non-whitefly species when they were offered separately. On the other hand, at 22-33°C, both S. parcesetosum larvae and adults consumed significantly more B. tabaci, A. gossypii and L. huidobrensis when they offered separately and no significant differences in the predation rate from T. ricini and T. urticae were recorded when they offered separately or together.
The results in Table 5 indicated that there were no significant differences in the preference by both larvae and adults of the predator for any whitefly species. The predation rates of S. parcesetosum larvae were means of 7.70 and 8.55 at 25°C as well as 7.60 and 8.15 at 22-33°C from B. tabaci and T. ricini, respectively.
| Table 5: | Predation rate by fourth larval instars and adults of Serangium parcesetosum by feeding on Bemisia tabaci and Trialeurodes ricini offered together on cucumber leaf discs at two different temperatures |
| Similar letter(s) in columns indicate no significant differences between the two whitefly species within the same S. parcesetosum stage and temperature at p≤5% (One-factor analysis of variance) | |
| Table 6: | Comparison of mean daily number of consumed unparasitized and parasitized puparia of Bemisia tabaci by Eretmocerus mundus kept together with Serangium parcesetosum fourth larval instars or adults on cucumber leaf discs at two different temperatures |
| Different letter(s) in columns indicate significant differences between unparasitized and parasitized puparia of B. tabaci within the same S. parcesetosum stage and temperature at p≤5% (One-factor analysis of variance) | |
While for S. parcesetosum adults, the predation rates were means of 8.75 and 9.25 at 25°C as well as 7.25 and 7.80 at 22-33°C from B. tabaci and T. ricini, respectively.
The results in Table 6 clearly showed that at both temperatures, both S. parcesetosum stages tested were significantly tended to avoid parasitized puparia and fed instead on unparasitized puparia of B. tabaci. The predation rates of S. parcesetosum larvae were means of 8.30 and 1.30 at 25°C as well as 7.35 and 1.15 at 22-33°C from unparasitized and parasitized puparia, respectively. While the predation rates of S. parcesetosum adults were means of 8.45 and 1.25 at 25°C as well as 7.05 and 1.05 at 22-33°C from unparasitized and parasitized puparia, respectively.
DISCUSSION
Due to pesticides resistance, which have been developed by agricultural pests (Kranthi et al., 2001), natural enemies could be an alternative method to suppress their populations (Al-Zyoud and Sengonca, 2004). Therefore, this study was set up to record new possible prey species for S. parcesetosum and to investigate its discrimination ability to the whiteflies’ parasitoid, E. mundus. However, the results of the present study on S. parcesetosum preference when the different prey species offered either separately or together showed that S. parcesetosum larvae and adults had significantly a general tendency in the prey preference toward the whitefly species tested, B. tabaci and T. ricini, consuming very few individuals from the mite, aphid and leafminer. However, Al-Zyoud and Sengonca (2004) reported that S. parcesetosum preferred significantly B. tabaci and T. vaporariorum rather than thrips, Frankliniella occidentalis (Pergande) (Thys., Thripidae); aphid, A. gossypii and mite, T. urticae when the prey species offered together. While, Legaspi et al. (1996) mentioned that when S. parcesetosum offered eggs of the corn earworm, Helicoverpa zea (Boddie) (Lep., Noctuidae); eggs of the tobacco hornworm, Manduca sexta (L.) (Lep., Sphingidae) and eggs and early instars of B. argentifolii together, S. parcesetosum did not feed on the eggs of H. zea and M. sexta presented, indicating a preference for B. argentifolii. Further more, according to Legaspi et al. (2001), S. parcesetosum is not as voracious on citrus blackfly, Aleurocanthus woglumi Ashby eggs as on B. argentifolii nymphs. However, it might be that nutrient differences among the different prey species could have a substantial impact on predator choice. The present results are in agreement with the previous ones, in which S. parcesetosum has a preference toward the whitefly species.
The way of offering the prey species has affected the predation rate by S. parcesetosum. In general, at both temperatures, S. parcesetosum larvae and adults consumed more individuals from all prey species when they offered separately rather than together. At 25°C, the predatory larvae consumed significantly more from all prey species when they offered separately rather than together and the predatory adults consumed significantly more from the non-whitefly species when they offered separately rather than together. Also, at 22-33°C, both S. parcesetosum larvae and adults consumed significantly more B. tabaci, A. gossypii and L. huidobrensis when they offered separately. It might be that S. parcesetosum had no alternative source of food, but to feed on more individuals from the different prey species when it was kept with them separately. This may be an advantage character for this predator in order to survive for some time in case of scarcity of the main prey (whiteflies).
The results of the current work on the preference of S. parcesetosum for the whiteflies, B. tabaci and T. ricini indicated that there were no significant differences in the preference by both larvae and adults of the predator for any whitefly species. To the best of our knowledge, this is the first record that S. parcesetosum could feed on the castor bean whitefly, T. ricini. However, Al-Zyoud and Sengonca (2004) stated that S. parcesetosum preferred significantly B. tabaci to T. vaporariorum. Abboud and Ahmad (1998) tested different species of whiteflies as possible prey for S. parcesetosum and they found that the whitefly, Paraleyrodes minei Laccarino is not suitable for the development of S. parcesetosum, while B. tabaci, D. citri and A. floccosus were suitable for the predator’ development. S. parcesetosum was developed faster on B. tabaci than on D. citri and A. floccosus, indicating that B. tabaci might be preferential to the other two-whitefly species (Abboud and Ahmad, 1998). From this study and the previous ones, it seems that S. parcesetosum is a specialist predator of many whitefly species. However, the degree of preference of S. parcesetosum for one whitefly species upon another might be due to size of the whitefly, thickness and hardness of the cuticle as well as many other physical and chemical characters of the different whitefly species. Moreover, in this regard, Patel et al. (1996) reported that this predator has been observed to be highly specific and feeding voraciously on the different stages of A. barodensis. According to Ahmad and Abboud (2001) as well as Al-Zyoud and Sengonca (2004), S. parcesetosum could feed on all B. tabaci developmental stages. Both larvae and adults of the predator are voracious feeders, capable of consuming large number of immature stages of B. argentifolii (Ellis et al., 2001). Regardless of the whitefly species used in the different studies, the results of the present study are in agreement with the previous ones, in which S. parcesetosum could feed on most of the whiteflies offered.
The present results on S. parcesetosum preference for parasitized prey demonstrated that S. parcesetosum larvae and adults tested were tended to avoid parasitized puparia of B. tabaci by E. mundus and fed instead on unparasitized puparia. In this regard, Al-Zyoud and Sengonca (2004) reported that the second and fourth larval instars as well as adult females and males of S. parcesetosum were tended to avoid parasitized puparia of B. tabaci by the parasitoid, Encarsia formosa Gahan (Hym., Aphelinidae) and fed instead on unparasitized ones. While, according to Hoelmer et al. (1994), the fourth larval instar and adult female of the whitefly predator, Delphastus pusillus (LeConte) (Col., Coccinellidae) showed a marked tendency to avoid B. tabaci puparia parasitized by the two aphelinid parasitoids, Encarsia tranvena (Timberlake) and Eretmocerus sp. nr californicus Howard in favor of unparasitized whitefly. The present study is agreed with the previous ones, in which the coccinellid predators are tended to avoid parasitized prey by the different parasitoids. Also, since the predator, S. parcesetosum tended to avoid feeding on parasitized prey, there is a feasible potential for integration of S. parcesetosum and the well-known whiteflies' parasitoid, E. mundus into a biological control program in order to provide a great level of B. tabaci suppression in Jordan and worldwide as well.