Disturbed Survival , Growth and Development of the Desert Locust Schistocerca gregaria by Different Extracts of Azadirachta indica ( Meliaceae ) and Nigella sativa ( Ranunculaceae )

The desert locust Schistocerca gregaria is an economically dangerous pest invading several countries in North Africa and West Asia. The present work aims at assessing the effects of Nigella sativa extracts, compared to Azadirachta indica extract Neemazal, on survival and development of this pest. Treatment of the newly moulted penultimate instar or the newly moulted last instar nymphs with Neemazal leads to the decrease in gained somatic weight. It, also, exhibiteds an inhibitory effect on the development of penultimate instar nymphs and intervenes with the metamorphosis program because that some nymphal-adult intermediates were formed. After treatment of the newly moulted penultimate instar nymphs with N. sativa extracts, the lethal effects of both the methanolic and petroleum ether extracts were exerted early in the same treated nymphs but no mortality rats were detected among the treated last instar nymphs by methanolic extract. Treatments of the same nymphs with N. sativa extracts led to the decrease in the body weight gain. The methanolic or petroleum ether extract significantly inhibited the nymphal development. Treatment with n-butanolic extract resulted in disrupted metamorphosis because some nymphaladult intermediates appeared proportionally to the concentration level. Treatments of the newly moulted last instar nymphs with N. sativa extracts deprived the nymphs to obtain normal somatic weight. Methanolic extract caused a slightly suppressed developmental rate. The n-butanolic extract exhibited a reverse action because significantly accelerated developmental rates, were recorded.


INTRODUCTION
Damage caused by the desert locust Schistocerca gregaria is a consequence of its polyphagous behaviour, high density of the population, and the nature to aggregate and swarm.Each individual gregarious locust is able to consume roughly its own weight (about 2 grams, or 0.7 ounces) in foliage daily (Lindsey, 2002).This partly explains how dense swarms of adults, or marching bands of hoppers, can inflict considerable economic harms during only a short time.
The use of chemical pesticides has been the main insect controlling approach during recent decades, but the widespread use of such chemicals has significant drawbacks, such as the development of strain resistance to insecticides (Garriga and Caballero, 2011), increased costs, handling hazards, concerns about insecticide
The 0-day old 4 th (newly moulted penultimate), 0-day old 5 th (newly moulted last) instar nymphs of S. gregaria were fed on fresh leaves of M. sativa after dipping in different concentration levels of each extract.A day after treatment, all nymphs (treated and control) were provided with untreated food plant.Ten replicates (one individual of nymph per each) were used for each concentration.Each individual nymph was isolated in a glass vial provided with a thin layer of sterilized sand as a floor.All vials were kept in a large cage having a suitable electric bulb.After feeding for 24 hrs on the treated leaves, all physiological criteria were studied.

Criteria studied:
Survival potential of the treated nymphs, or their control congeners, is a reverse ratio of the mortality % in the meaning of more mortalities lesser survival potential.The insect growth is usually predicted by the weight gain.It was calculated as follows: initial weight (before the beginning of experiment) -final weight (at the end of experiment).
The developmental rate of the nymphs can be expressed by the developmental duration.Developmental duration was calculated by the Dempster's equation (1957) and the developmental rate was calculated by Richard's equation (1957).
Nymphal-adult intermediates were observed and calculated in % as disturbed morphogenesis of the desert locust.

Statistical Analysis of Data:
Data obtained were analyzed by the Student's t-distribution, and refined by Bessel correction (Moroney, 1956) for the test significance of difference between means.

A) Mortal Potency of the Plant Extracts Against Nymphs of S. gregaria.
Five concentration levels of methanolic, petroleum ether or n-butanolic extract of each of the cultivated plant Nigella sativa (Ranunculaceae) as well as six concentration levels of the neem extract, Neemazal (Azadirachta indica, Meliaceae) were applied against the early penultimate (4 th ) or last (5 th ) instar gregarious nymphs of Schistocerca gregaria.After 24 h of treatment, all mortalities were observed for nymphs.Also, the nymphal mortality was recorded along each of the nymphal instars.
After treatment of penultimate instar nymphs with the highest concentration level, all insects died while 60.0% mortality was recorded at conc.level 3.7% of Neemazal.However, other mortalities were recorded in the resulted 5 th instar nymphs (40.0 and 20.0 % mortalities at conc.levels 3.7 and 1.8 %) (Table1).After treatment of last instar nymphs, all insects died at the highest conc.level while 70.0%mortalities was recorded at conc.levels 3.7 and 1.8% (Table 2).
Data of the mortal potency of the N. sativa extracts are arranged in Table (3).After treatment of penultimate instar nymphs, the lethal effects of both the methanolic and petroleum ether extracts were exerted early in the same treated nymphs but the lethal effects of n-butanolic extract lately appeared during the next nymphal instar.Some different results of toxicity were obtained for the N. sativa extracts after treatment of the last instar nymphs (see Table 4).No mortality %s were observed among the treated last instar nymphs by the methanolic extract.According to the data, the lethal action of petroleum ether extract increased as the concentration level was increased (20 and 30 mortality %s at concentration levels 15 and 30 %).A similar dose-dependent mortality could not be observed after treatment of the last instar nymphs with n-butanolic extract which caused the maximal % (30%) at concentration level 7.5%.B) Influenced Growth and Development of S. gregaria by the Plant Extracts: 1-Effects of Neemazal: As summarized in Table (1), penultimate instar nymphs gained somatic weight less than that of control congeners (as for examples: 245.3±50.0mg at concentration level 3.7% vs. 358.5±69.4mg of control congeners).Also, the successfully moulted last instar nymphs were prohibited to gain normal somatic growth, i.e. the weight gain decreased, albeit insignificantly, by the action of Neemazal.Such decreasing weight gain was in a dose-dependent course.Depending on the data of the same table, Neemazal exhibited an inhibitory effect on the development of both penultimate and last instar nymphs since the nymphal duration in penultimate instar was highly significantly prolonged (especially at the concentration level: 3.7, 1.8, 0.9 and 0.4%: 19.0±2.8,17.7±3.2,13.2±2.8and 15.5±3.9 vs. 09.6±2.6 days days of control nymphs).A similar inhibitory effect of this neem extract on the development of last instar nymphs was calculated (especially at the concentration levels 1.8 and 0.9%: 15.8±4.0 and 15.9±3.9days vs. 12.3±1.2days of control nymphs).Another calculated parameter may substantiate this finding where the developmental rate of penultimate instar nymphs was conspicuously regressed by the action of Neemazal parallely to the concentration level.On the other hand, less suppressing action of the extract could be detected in the last instar nymphs.
Also, the program of development and metamorphosis was disrupted because some nymphal-adult intermediate creatures appeared (Plate 1).However, no certain trend of such disrupted program was recorded.2), show a slight depressing effect of Neemazal on the weight gain.Also, Neemazal exhibited pronouncedly inhibitory effect on the developmental duration of nymphs nearly in a dose-dependent manner.The most detrimental effect (18.1±2.1 vs. 12.9±2.9days of control congeners) was recorded at the concentration level 0.9%.Subsequently, the developmental rate decreased as the concentration level was increased.Neemazal, at these three concentration levels, intervened with the metamorphosis program since some nymphal-adult intermediates were formed (20, 10 and 10% at concentration levels 3.7, 1.8 and 0.9%, respectively) (Plate 1).

1) Effects of the N. sativa extracts:
Table (3) contains data of the most important growth and development parameters of S. gregaria after treatment of penultimate instar nymphs with the N. sativa extracts.With regard to the somatic growth of penultimate instar nymphs, depressed weight gain was generally recorded as an effect of all N. sativa extracts.The most dramatically depressed weight gain was observed at the highest concentration level of methanolic extract and n-butanolic extract (197.6±76.3 vs. 417.6±47.0mg of control nymphs and 269.7±50.2 vs. 361.3±61.9mg of control nymphs, respectively) but at concentration level 7.5% of petroleum ether extract (337.3±51.6 vs. 417.6±47.0mg of control nymphs).
The data in the same table show a significant inhibitory effect on the developmental duration of penultimate instar nymphs, unexceptionally, by the methanolic extract (10.61.4,10.7±1.5, 10.1±1.3 and 10.1±1.2 days at concentration levels 15.0, 7.5, 3.7 and 1.8 % of methanolic extract, compared with 8.3±2.1 days of control nymphs) and petroleum ether extract (10.9±1.9, 10.9±2.1, 11.0±1.5 and 10.9±1.9 days at concentration levels 15.0, 7.5, 3.7 and 1.8 %, compared with 8.3±2.1 days of control nymphs).The n-butanolic extract exhibited remarkably inhibitory effect or slightly enhancing one (11.1±1.0 at concentration level 30.0 % vs. 9.2±1.9days of control nymphs) on such duration.An odd datum of the developmental duration after treatment with methanolic extract was 3.6±1.2days (in comparison with 8.3±2.1 days of control nymphs) i.e., such extract enhanced the development at the highest concentration level.However, no certain trend could be observed for the enhancing effect of the methanolic extract and petroleum ether extract.Furthermore, the developmental duration was prolonged or shortened in no certain trend after treatment with n-butanolic extract.10.0 5.5 18.1 ± 2.1 d 644.1 ± 107.1 a 10.0 0.9 00.0 7.2 13.8 ± 2.7 a 634.1 ± 110.0 a 10.0 0.4 00.0 7.5 13.3 ± 2.2 a 662.2 ± 114.5 a 10.0 0.2 00.0 7.8 12.9 ± 2.9 674.0 ± 165.4 10.0 Controls Also, the growth and developmental criteria of the next instar nymphs were affected by these N. sativa extracts as clearly shown in the same table.Depending on the available data, the successfully moulted last instar nymphs appeared with depressed weight gain, irrespective of the N. sativa extract or its concentration level.However, the most drastic depressing effect was observed for only the two higher concentration levels of methanolic extract (518.1±109.3 and 550.0±117.5 mg at concentration levels 30.0 and 15.0%, respectively, vs. 688.9±110.3mg of control nymphs).It is important to mention that the treatment with only n-butanolic extract resulted in disrupted metamorphosis because some nymphal-adult intermediates appeared proportionally to the concentration level (Plate 1).
Just a look at the data of Table (4) reveals some insignificant effects of N. sativa extracts on growth and development of S. gregaria after treatment of last instar nymphs.Also, these last instar nymphs were deprived to obtain normal somatic weight but their calculated weight gain slightly decreased, irrespective of the extract.For some details, treatment with methanolic extract resulted in a slight prolongation of the developmental duration and subsequently slightly depressed developmental rate.The n-butanolic extract exhibited a reverse action because insignificantly shortened durations, and subsequently slightly fastened developmental rates, were recorded.
In addition, no effect was observed on the metamorphosis program by methanolic or n-butanolic extract.Only the petroleum ether extract exerted a drastic effect on such program because some intermediates appeared (40% of nymphal-adult intermediates at 15.0%).

1) Insecticidal Efficiency of the Plant Extracts against S. gregaria:
So many institutions have been engaged with the search for some environmentally safe control agents in order to avoid the disadvantages and hazards of the synthetic insecticides.A great part of efforts have been achieved for the investigation and re-examination of plant sources to obtain natural compounds which may have toxic , repellent , anti-feedant or anti-hormonal characteristics (Thomas and Callaghan, 1999).The most famous plant species for several decades ago is the neem tree Azadirachta indica from which hundreds of products and preparations were extracted and assessed against different insect pests for protecting the health and agronomical systems.As a contribution in this context, in the present study, Nigella sativa (Ranunculaceae) was extracted by methanol, petroleum ether and n-butanol for investigating its potential effects against the economically destructive desert locust S. gregaria.Also, Neemazal (with 20 % azadirachtin content) was assessed as a comparative parameter for these extracts.
Despite of the plenty of literature about the bioactivity of the azadirachtin (Azt.) and other neem products and preparations against several insect species, it is sufficient to look on the following few examples.High mortality rates of the brown plant hopper Nilaparvata lugens (Homoptera) were caused by higher concentrations of Azt.(Saxena and Khan, 1985).Some products of Az. indica exhibited a larvicidal activity in the horn fly Haematobia irritans, stable fly Stomoxys calcitrans and house fly Musca domestica (Miller and Chamberlain, 1989).The oils pressed from seeds of Az. indica achieved mortality rates of 65-100 % in S. gregaria (Schmutterer and Freres, 1990;Nicol and Schmutterer, 1991).On the other hand, no acute toxic effect of azadirachtin applied against the 5 th instar larvae of Spodoptera mauritia, was observed (Jagannadh and Nair, 1992).Osman (1993) observed some different mortalities of Pieris brassicae after treatment of 1-day old 5 th instar larvae with 5.0 and 2.5 % azadirachtin.Also, high mortality of S. gregaria, red locust Nomadacris septemfasciata and variegated grasshopper Zonocerus variegates was caused by the neem oil (Schmutterer et al., 1993).The neem seed and kernel powder applied directly, or as aqueous extract, killed Clavigralla tomentosicollis (Mitchell et al., 2004).Azadirachtin, also caused complete mortality of N. lugens nymphs at 1.0 ppm azt.(Senthil Nathan et al., 2007).Mortality of N. lugens was associated mainly with failure to moult and the nymphs died after several days (Senthil Nathan et al., 2007).Azadirachtin caused increasing mortality of Spodoptera exigua (Yoshida and Toscano, 1994), Trialeurodes vaporariorum (von Elling et al., 2002) and Cnaphalocrocis medinalis (Senthil Nathan et al., 2006 a).Recently, Azadirachtin exerted a lethal action increasingly with the age of pupae after treatment of the prepupae of Rhynchophorus ferrugineus (Abdel-Ghaffar et al., 2008).Also, a significant reduction of the larval and pupal survival of the blowfly Chrysoma megacephala and M. domestica after mixing the fresh beef (as a food) with a neem product (0.24 % Azt.content) (Siriwattanarungsee et al., 2008).Some other neem seed extracts and preparations were assessed against several insect pests, such as Margosan-O (0.2 % Azt.content) and Neemazal (20 % Azt.content).After treatment of larvae with Margosan-O, various degrees of mortality of S. littoralis (Meisner and Nemny, 1992), of Earias insulana (Meisner et al., 1981), of Ostrinia nubilalis (Meisner et al., 1991), of the European leafroller Archips rosanus (AliNiazee et al., 1997), of the false stable fly Muscina stabulans was caused after continuous feeding of larvae on Margosan-O treated diet (Ghoneim and Al-Dali, 2002), of M. domestica (Amer et al., 2004) were recorded.Referring to another famous neem seed extract, Neemazal, the lethal effects were reported for several insect pests, such as S. littoralis (Ghoneim et al., 2000), M. domestica (Mohamed et al., 2000), Tribolium castaneum (Athanassiou et al., 2005).
In the light of all these aforementioned results for the neem products against the survival of different insect pests, and as a contribution for searching alternative control agents to the desert locust S. gregaria, the lethal action of Neemazal was investigated in the present study.The newly moulted nymphs of the later instars (4 th and 5 th ) of S. gregaria were treated (through the fresh food plant) with Neemazal (20 % Azt.content) for assessing its mortal potency because the toxicity of plant extracts depends on the physiological age of larvae (Adeyeye and Blum, 1989).After treatment of penultimate or last instar nymphs with the highest concentration level, all insects died.However, the present results of Neemazal toxicity on S. gregaria agree, to a great extent, with other results on different insect species.The partial or complete mortality of S. gregaria, in the present study, may be attributed to the feeding inhibition which usually leads to continuous starvation and subsequently death (Ghoneim et al., 2000).Specifically, the deaths of botanical-treated penultimate instar nymphs of S. gregaria in the present study may be due to the inability of the moulting bodies to swallow sufficient volumes of air to split the old cuticle and expand the new one during ecdysis (Mordue and Evans, 1987;Linton et al., 1997).In addition, the deaths of last instar nymphs of S. gregaria may be due to a metamorphosis inhibiting effect of the plant extract, which is possibly based on the disturbance of the hormonal regulation (Al-Sharook et al., 1991) because the prevention of the metamorphosing ecdysis, and subsequently death, could be attributed to the reduction in ecdysteroid peak or interference with the release of eclosion hormone (Sieber and Rembold, 1983).
The present results of toxicity caused by N. sativa come in an agreement with those results reported by several authorities using different plant species against various insect pests.Just a look on the following examples may be sufficient, Chiu et al. (1985) reported that at 400 ppm toosendanin (extract from Melia toosendan) caused 80 % mortality to 3 rd instar and 580 ppm caused 75 % mortality to 5 th instar Pieris rapae.Water based extracts from the fruits and leaves of Melia azadirach yielded mortality rates between 93 and 100 % in nymphs of Locusta migratoria migratorioides (Wen and Schmutterer, 1991).The aqueous extract of Koelreuteria paniculata (Laxm.)(0.15%).causing a significant increase in the larval mortality (68.3%) of Anticarsia gemmatalis (Huebner) (Martins et al., 2012).Application of the palm oil on S. gregaria induced mortality rate that increased with dosage (Wilps et al., 1993).Against the same acridid species, topical application of Melia volkensii extracts caused 32.5 % mortality in the laboratory-reared nymphs and 27.8 % mortality in the field-collected nymphs (Nasseh et al., 1993).Feng et al. (1995) observed no mortality of Spodoptera litura larvae even at 600 or 3000 ppm toosendanin.Methanolic extracts from the leaves of Chukrasia tabularis var velutina and Swietenia macrophylla caused high mortality among the Chinese rice grasshopper Oxya chinesis (Xiao Dong et al., 1997).Pascual-Villalobos and Robledo (1998) reported higher mortalities in larvae of T. castaneum by the extract from Ajuga iva.Topical application of leaf and whole plant extracts of Ageratum conyzoides (Asteraceae) to the penultimate instar nymphs of S. gregaria resulted in nymphal mortality (Sharda et al., 2000).Crude ethanolic extracts of A. iva or Ajuga pseudoiva have insecticide activity against some Lepidoptera (Simmonds and Blaney, 1992 ;Benjannet et al., 2001).Topical application of ethanolic extracts from Cyprus rotendus (Cryperaceae) to penultimate or last instar nymphs of S. gregaria caused increasing nymphal mortality parallely to the dose level (El-Sokkary, 2003).However, the present plant extracts may contain certain ingredients affecting the homeostasis leading to increased body water loss and subsequently the death (Amer et al., 2004).Because the plant species, Peganum harmala, as for example, is a rich source of β-carboline alkaloids which, and other secondary metabolites, may explain the toxic effects on S. gregaria (Kartal et al., 2003).Further investigation should be conducted in future for exploring the secondary metabolites, alkaloids or other active components, in the extracts of the present tested plant N. sativa which cause the disturbance or imbalance of the enzymatic pattern or hormonal hierarchy responsible for the maintenance of life and regulation of different physiological processes (Dorn et al., 1986).

1) Inhibited Growth, Retarded Development and Disturbed Metamorphosis of S. gregaria by the Plant Extracts: a) Inhibited Growth of S. gregaria:
Because the body weight, and hence the weight gain, is one of the valuable indicators for evaluating growth (Armbruster and Hutchinson, 2002), the weight gain of nymphs was determined in the present study.After treatment of the penultimate instar nymphs of S. gregaria with Neemazal, the somatic weight gain was less than of control nymphs.Also, the treatment of the last instar nymphs with Neemazal resulted in a slight decreased body weight gain.These results are, however, in accordance with several results using the azadirachtin or other neem preparations.Growth inhibition was recorded for the migratory locust L. migratoria after treatment with a compound from the neem tree Az. indica (Sieber and Rembold, 1983), the lepidopteran Spodoptera mauritia larvae after treatment with azadirachtin (Jagannadh and Nair, 1992), the stable fly S. calcitrans and house fly M. domestica by azadirachtin (Miller and Chamberlain, 1989), the desert locust S. gregaria by azadirachtin (Annadurai and Rembold, 1993), the cotton leaf worm S. litoralis after treatment of larvae with the neem preparation, Neemazal (Ghoneim et al., 2000) or Margosan-O (Mohamed et al., 2000), the false stable fly Muscina stabulans after treatment of larvae with Margosan-O (Al-Dali et al., 2003), the house fly M. domestica after larval treatment with Margosan-O (Amer et al., 2004), the brown plant hopper Nilaparvata lugens after treatment the nymphs with different neem extracts (Senthil Nathan et al., 2007), the blowfly Chrysoma megacephalala and house fly M. domestica after mixing a neem product (0.24 % Azt.content) with beef (as a food) (Siriwattanarungsee et al., 2008), and the red palm weevil Rh. ferrugineus after treatment of prepupae with azadirachtin (Abdel-Ghaffar et al., 2008).In contrast, no significant effect of a neem extract on the body weight gain of Pieris brassicae larvae was observed (Osman, 1993).
In addition to the neem seed extract, Neemazal, different extracts from N. sativa were assayed in the present study to investigate possible effects on growth of S. gregaria in the present study.Concerning the growth inhibition by the N. sativa extracts, treatment of penultimate instar nymphs resulted in suppressed body weight gain.However, the most drastic suppressing effect on the weight gain was exhibited at the highest concentration level (30%) of the methanolic and n-butanolic extracts.After treatment of the last instar nymphs, the normal somatic growth was prohibited when compared with that of the control congeners.
As clearly seen in the present study, methanolic, petroleum ether and nbutanolic extracts from N. sativa prohibited the growth of S. gregaria nymphs.These results agree with several reported results for other insect species using other plant extracts.Essential oils of garlic significantly suppressed the growth rate of the coleopterans Sitophilus zeamais and T. castaneum (Huang et al., 2000).Acetonic and ethanolic extracts from tubercula and various compounds of Aristolochia pubescensi inhibited the larval growth of T. castaneum (Nascimento et al., 2004).Melia volkensii (Meliaceae) extract exhibited a potent growth inhibitor effect on the cabbage looper Trichoplusia ni (Lepidoptera) (Akhtar and Isman, 2004).A methanolic extract from the roots and aerial parts of Myrtillocactus geometrizans (Cactaceae) disturbed the growth of Spodoptera frugiperda and Tenebrio molitor (Cespedes et al., 2005).Similar growth inhibition was reported for Trichilia americana extract in S. littoralis larvae and for Melia.azedarach extract in the rice leaffolder Cnaphalocrocis medinalis (Lepidoptera) (Senthil Nathan, 2006).Jojoba oil prohibited the pupal growth of the red palm weevil Rh. ferrugineus (Abdel-Ghaffar et al., 2008) but did not affect the growth of larval growth of M. domestica (Amer et al., 2004), etc.
The growth inhibition in S. gregaria , by the action of azadirachtin or other plant extracts in the present study, may however be caused as a result from the blocked release of morphogenic peptides, causing alteration in ecdysteroid and juvenoid titers as suggested by Sieber and Rembold, 1983 ;Barnby andKlocke, 1990 andLinton et al., 1997.Also, some possible direct effects of azadirachtin (as represented by Neemazal, in the present study) , N. sativa extracts may affect the tissues and cells undergoing mitosis (Nasiruddin and Mordue, 1994) .a) Retarded development of S. gregaria: In the present study on S. gregaria, the treatment of penultimate instar nymphs with Neemazal, resulted in retarded development since the developmental duration was prolonged and developmental rate was regressed parallelly to the concentration level.Also, a similar inhibitory effect of Neemazal was exerted on the development after treatment of the last instar nymphs nearly in a dose-dependent fashion… More or less, prolonged developmental duration was a good indicator to the inhibited development of the migratory locust L. migratoria after treatment with azadirachtin (Urishalom et al., 1988), of the desert locust S. gregaria after treatment with the seed oil from Az. indica (Nicol and Schmutterer, 1991), of S. mauritia after treatment with azadriachtin (Jagannadh and Nair, 1992), of the lepidopteran S. exigua after treatment with a neem extracts (Yoshida and Toscano, 1994), of the hemipteran Spilostethus ponchrus after treatment with azadirachtin (El-Sherief, 1998), of the orthopteran Euprepocnemis plorans after treatment with the neem preparation, Margosan-O (Mohamed, 1998), of the dipteran M. domestica after treatment with the neem preparation, Neemazal (Mohamed et al., 2000), of the lepidopteran S. littoralis after treatment with the neem preparation, Neemazal (Ghoneim et al., 2000), of the homopteran Trialeurodes vaporariorum after treatment with Azt.(von Elling et al., 2002), of the dipteran M. stabulans after treatment with the neem preparation, Margosan-O (Al-Dali et al., 2003), of the coleopteran Rh. ferrugineus by azadirachtin (Abdel-Ghaffar et al., 2008)., etc… On the contrary, shortened developmental duration indicating an induced development had not observed for S. gregaria after treatment the nymphs with Neemazal, but reported for other insect species such as: M. domestica (Amer et al., 2004) In the present study, treatment of the penultimate instar nymphs with N. sativa extracts resulted in changed development of treated nymphs by exhibited a remarkable inhibitory effect (significantly prolonged developmental duration).Also, slightly retarded development by methanolic extract but slightly enhanced development by n-butanolic extract was recorded after treatment of the last instar nymphs.Shortly, N. sativa caused a significant retardation or enhancement of the development of S. gregaria depending on the extracted ingredients because the butanolic extract (after treatment of the penultimate instar nymphs) and methanolic extract (after treatment of the last instar nymphs) caused a retarded development while other extracts promoted this serious physiological process.However, the retarded development of S. gregaria by some extracts of the present two plant species (neem and N. sativa) agree with some results obtained for several insect species by the action of extracts from different plant species as reported herein.
Extracts from M. volkensii (Meliaceae) caused a conspicuous prolongation of larval development in the orthopteran S. gregaria and the mosquito Aedes aegypti (Mwangi and Rembold, 1988 ;Wilps et al., 1993).Also, Amr et al. (1995) observed a significant prolongation in the larval duration of S. littoralis by the ethanolic extract from Nerium oleander which, also, caused similar prolongation in the developmental duration of M. stabulans (El-Shazly et al., 1996).Similar effects were observed for hormone) causing the inhibition or delay of a number of physiological processes, such as metamorphosis (Josephrajkumar et al., 1999).Extracts of different species of Rutaceae interfered with neuronal as well as neuroendocrine and endocrine components of moult regulation (cf.Richter et al., 1997).Hence, the neem extract Neemazal , N. sativa extracts affected the hormonal events essential to the nymphaladult transformation in S. gregaria, in the present study (moulting, juvenile and eclosion hormone, in particular).Also, the suggestion of Senthil Nathan et al., (2007) may be appreciated because the feeding of N. lugens nymphs on neem-treated plants for some days resulted in damage to physiological processes essential to the development.However, further investigation should be conducted in the future to disclose this questionable issue to point out the mode of action of the active components contained in the present plant extracts.
Plate 1: Nymphal-adult intermediates of Schistocerca gregaria as a disturbed metamorphosis program after the nymphal treatments with the present plant extracts.(A) Normal adult.(B) Normal last instar nymph.(C) a nymphal-adult intermediate.

Table 1 :
Survival, growth and developmental effects of the neem extract, Neemazal, on the desert locust Schistocerca gregaria after treatment of the early penultimate instar nymphs.

Table 2 :
Survival, growth and developmental effects of the neem extract, Neemazal on the desert locust Schistocerca gregaria after treatment of early last instar nymphs.Conc., Develop.rate, Inter., a, d: See the footnote of Table (1).

Table 3 :
Survival, growth and developmental effects of Nigella sativa extracts on the desert locust Schistocerca gregaria after treatment of the early penultimate instar nymphs.Develop.rate, Inter., a, b, c, d: See the footnote of Table (1).*: One nymph only could survive.

Table 4 :
Survival, growth and developmental eefcts of Nigella sativa extracts on the desert locust Schistocerca gregaria after treatment of the early last instar nymphs.