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Crop Protection 38 (2012) 7e14

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Crop Protection

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Effect of neemarin on life table indices of Plutella xylostella (L.)

Nadeem Ahmad, M. Shafiq Ansari*, NazrussalamDepartment of Plant Protection, Faculty of Agricultural Sciences, Aligarh Muslim University, Aligarh-202 002, India

a r t i c l e i n f o

Article history:Received 15 October 2011Received in revised form4 March 2012Accepted 14 March 2012

Keywords:Plutella xylostellaPotential fecundityNet reproductive rateIntrinsic rate of increaseDoubling time

* Corresponding author. Tel.: þ91 9412133609.E-mail address: mohdsansari@yahoo.com (M.S. An

0261-2194/$ e see front matter � 2012 Elsevier Ltd.doi:10.1016/j.cropro.2012.03.006

a b s t r a c t

The effects of neemarin at 5, 10, 15 and 20 mg l�1 on the life table indices of Plutella xylostella (L.) werestudied on cauliflower in the laboratory. Survivorship was increased with increasing concentrations. Atotal of 69% eggs hatched at 20 mg l�1 compared 85% in the control. Mortality (dx) of 1st instars washigher than the other instars in both exposed and unexposed individuals. Life expectancy (ex) was high inthe untreated control and reduced at 20 mg l�1. Development times of immatures were prolonged to 32days at 20 mg l�1 as compared to 18.6 days in the untreated control. Neemarin significantly reduced theemergence of adults. Potential fecundity (Pf) was 34 females/female/generation at 20 mg l�1 and 92 inthe control. The net reproductive rate (R0) was significantly reduced with the increase in concentration.The intrinsic rate of increase (rm) and finite rate of increase (l) were significantly decreased at 20 mg l�1

as compared to other concentrations tested and in the control. Mean generation time (Tc) and correctedgeneration time (s) were prolonged at 20 mg l�1 and significantly differed to those of the untreatedcontrol. Doubling time (DT) was significantly extended to 28.4 days at 20 mg l�1 as compared to 6.1 daysin the control.

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1. Introduction

The diamondback moth (DBM), Plutella xylostella (L.) (Lepidop-tera, Yponomeutidae) is a cosmopolitan and oligophagous pest ofcruciferous crops (Thorsteinson, 1953). It is present wherever itshost plants exist and is considered to be the most widely distrib-uted among all the Lepidoptera (Shelton, 2004; Zalucki andFurlong, 2008) because of the diversity and abundance of hostplants (Fathi et al., 2011; Soufbaf et al., 2011), lack or distribution ofits natural enemies, and high reproduction potential with up to 20generation per year (Hui et al., 2010) and has an ability to rapidlyevolve resistance to insecticides (Sayyed et al., 2004; Shelton,2004). P. xylostella attacks the crop from the nursery stageonwards and can cause 52% loss in marketable yield in cabbage(Krishnakumar et al., 1984; Liang et al., 2003; Shelton, 2004) whileSrinivasan (1984) reported 90e92% losses could occur if cabbage isleft unprotected. Lingappa et al. (2000) reported that losses couldvary from 30 to 100%. In India, the losses due to diamondback mothare estimated to be US$ 16 million annually in a cultivated area ofcabbage of 0.51 million ha (Mohan and Gujar, 2003). Outbreaks ofthe diamondback moth in South-East Asia sometimes have causedmore than 90% crop loss (Verkerk and Wright, 1996; Ahmad et al.,2009) and its infestation has forced growers to plough down the

sari).

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standing crop in spite of multiple insecticide applications (Abroet al., 2004; Ahmad et al., 2009). Development of high toleranceto most of the insecticides and destruction of natural enemies aswell as associated environmental problems (Kfir, 2002; Liang et al.,2003; Xu et al., 2004) have increased the interest of consumers andgrower in natural insecticides originated from the plants and theirusage has increased in recent years (Isman, 2006). Therefore,botanical products are useful and desirable tools in most of the pestmanagement programmes because they are effective and often nontoxic to natural enemies with low environmental impact(Schmutterer, 1990, 1995; Haseeb et al., 2004; Xu et al., 2004).

Azadirachtin (a tetranortriterpenoids) is the predominant activeinsecticidal component found in neem seeds and leaves(Butterworth and Morgan, 1968) and is best known derivative(Broughton et al., 1986) that has been effectively used against morethan 400 species of insects, including many key crop pests, and hasproved to be one of the most promising plant ingredients forintegrated pest management (Schmutterer and Rembold, 1980;Schmutterer, 1990; Deling et al., 2005; Hasan et al., 2011). Thiscompound displays an array of effects on insects, acting as a phag-ostimulant and oviposition deterrent, and preventing insect larvaefrom developing into adults (Schmutterer, 1995; Mordue andBlackwell, 1993). Azadirachtin affects feeding, through chemore-ception (primary antifeedancy) by the blocking of input fromreceptors that normally respond to phagostimulants (Mordue andBlackwell, 1993).

N. Ahmad et al. / Crop Protection 38 (2012) 7e148

Stark and Wennergren (1995) have proposed demographictoxicological analysis that incorporates life table parameters inthe context of toxicology. It is a process that allows one tocompare life table parameters for unexposed populations withthose populations exposed to various concentrations of a toxicant.Therefore, it is an appropriate approach that takes into account allthe biological parameter effects that a toxicant might have at thelevels of organization higher than the individual (Stark et al., 1997,1998, 2004). Life table response experiments (LTREs) are beingincreased to measure multiple end points of the effect and havebeen recommended as a superior laboratory toxicologicalendpoint (Stark et al., 1997). Estimating toxicant effects on pop-ulations is complicated by the fact that exposures can result ina part of population dying while surviving individuals may beimpaired (Stark and Wennergren, 1995). Furthermore, somespecies can withstand a high level of mortality and recoverquickly because they have a high population growth rate, shortgeneration time, early onset of reproductive activity or a combi-nation of these attributes, other species may become extinct afterexposure to a toxicant at a concentration that does not kill allindividuals because sub lethal effects severely impact individuals(Stark et al., 2007).

Few studies have been published on the use of demographicalanalysis and similar measures of population growth rate wereevaluated on the effect of pesticides on insects (Stark et al., 1997;Stark and Banks, 2003; Rezaei et al., 2007). These results wouldfinally provide a better understanding and prediction of the totaleffect of insecticide at the population level of a species (Kareivaet al., 1996; Forbes and Calow, 1999). Stark and Banks (2003) havealso suggested that demographic toxicological data are superior toother types of toxicity data. The aim of the present study is todetermine the effects of neemarin on life table indices ofP. xylostella in order to gain understanding and valuable insightregarding the mortality and development, reproduction rate,intrinsic rate of increase and generation time so that amanagementprogram may be formulated for P. xylostella on cauliflower.

2. Materials and methods

2.1. Insect rearing and experimental condition

More than 200 larvae of P. xylostellawere collected in September2009 from the cultivated field of cauliflower, Brassica olearaceabotrytis Var. Pusa Bahar at the Department of Plant Protection,Faculty of Agricultural Sciences, Aligarh Muslim University, Aligarh,India. They were kept in plastic cups (250 ml) on filter paper andeach cup containing 5 larvae and then placed at 25 � 2 �C with70 � 5% relative humidity and a photoperiod of 12L:12D. Freshcauliflower leaves were provided as food for the larvae and changeddaily until pupation. Pupae were collected and kept in another jar(10 � 15 cm) for emergence. Emerged adults were then transferredin to glass jars (25� 25 cm) each containing five pairs of adults andprovided with 10% sugar solution soaked in cotton wick as a foodfor adults. A fresh cauliflower leaf was kept in each jar for ovipo-sition. Freshness of leaf was maintained by wrapping moist soil onto the leaf petiole which was then covered over with aluminum foiltied with light polythene sheet. They were reared under theseconditions for up to three generations to acclimatize the DBM andthe 4th generation was used for bioassay.

2.2. Preparation of neemarin concentration

Neemarin� (0.15% EC azadirachtin) was obtained from M/SBiotech International Ltd. New Delhi, India. Four concentrations(20, 15, 10 and 5mg l�1) were prepared separately by slowly adding

the material in 100 ml of distilled water stirring consistently for30 min at room temperature. Distilled water was used as a control.

2.3. Bioassay

Leaf discs (2.5 cm) of cauliflower var. Pusa Bahar were dipped in20, 15, 10 and 5 mg l�1 of neemarin for 2 min and air dried at roomtemperature for 30 min. For the experimental control, leaf discs(2.5 cm) of cauliflower were dipped into distilled water. Animpregnated leaf disc was then kept in a plastic jar (100 ml) in towhich five newly moulted 4th instars taken from the stock cultureand released. The year was then covered with muslin cloth fixedwith rubber band for aeration. Each treatment was replicated sixtimes. A parallel control was also run for each treatment. Leaf discswere removed after 24-hr and the fresh untreated leaves wereprovided to the surviving larvae until pupation. Dead larvae andmalformed pupae were discarded. Pupae were sorted by sex andkept for emergence.

2.4. Effect of neemarin on life table indices

Freshly emerged male and female adults from the abovebioassay experiment were paired and kept in a glass jar(20 � 15 cm) provided with 10% sugar solution soaked in cottonwick as food along with a fresh leaf of cauliflower for oviposition.Freshness of leaf was maintained by wrapping moist soil on to theleaf petiole and covered over by aluminum foil tied with thinpolythene sheet as indicated previously. Freshly laid eggs werecounted and kept in batches of 10 to make a cohort of 300 eggs foreach concentration of Neemarin for construction of life table anda parallel untreated control was also run with the same number ofeggs (cohort). Hatched and unhatched eggs were counted. Aliveand dead larvae were recorded daily. Pupae were sorted fromdifferent treatments and kept for emergence in separate glass jars(10 � 10 cm).

2.5. Effect of neemarin on female fertility

Freshly emerged females andmales of P. xylostella obtained fromabove experiment were paired and each pair was kept in a separateglass jar (25 � 15 cm). A batch of 10 pairs replicated three times forall treated and untreated control experiments were used. Theywere provided with 10% sugar solutions soaked in cotton wick asfood along with a fresh leaf of cauliflower for oviposition as above.A newmale was released into glass jars whenever male died. Thus,each female had a male available for mating during its life time.Eggs laid by each female were recorded daily from the day afteremergence till death of each female. The number of eggs wasdivided on the basis of a sex ratio of 1:1 to get the number of femalebirths (mx). Life table was constructed followed themethod of Birch(1948) and Southwood (1978). Expectancy of life was calculated byex ¼ Tx/Ix. For adults, survival rate from birth to age x (Ix), fecundity(mx, total number of offspring produced at age x) was measuredaccording to Birch (1948). From these data, potential fecundity(Pf ¼ P

mx), reproduction rate (R0 ¼ Ix$mx), the intrinsic rate ofincrease (rm ¼ e�rmx$ Ix$mx ¼ females/female/day) and finite rate ofincrease (l ¼ ermfemales/female/day) were determined. Meangeneration time (Tc) is the mean period over which progeny areproduced and is estimated by the formula, Tc ¼ P

[Ix$mx$x]/P(Ix$mx), while corrected generation time (s) is defined as the

period from the birth of individuals to the birth of offspring whichis calculated by the formula, s ¼ loge R0/rm. Doubling time (DT) isdefined as the time required for the population to double itsnumber and is calculated by DT ¼ ln2/rm. The differences in rm andother life table parameters were tested for significance by using the

N. Ahmad et al. / Crop Protection 38 (2012) 7e14 9

Jackknife method (Meyer et al., 1986; Maia De et al., 2000). Jack-knife pseudo-values were calculated with a computer program (LaRossa and Kahn, 2003).

2.6. Effect of neemarin on development of P. xylostella

Thirty pairs of freshly emerged adults of P. xylostella obtainedfrom 4th instars that had ingested 5, 10, 15 and 20 mg l�1 of nee-marin were selected and each pair was kept in a separate glass jar(20 � 15 cm). They were provided with 10% sugar solution soakedin cottonwick as food for adult alongwith a fresh leaf of cauliflowerfor oviposition. Freshness of leaf was maintained by wrappingmoist soil on to the petiole and covered over by aluminum foil tiedwith thin polythene sheet. Freshly laid eggs were counted and keptin a batch of 10 and replicated 10 times for each concentration andthe control. Total duration of incubation was recorded for eachconcentration and the control. After hatching, development timesof 1st, 2nd, 3rd and 4th instars, prepupa and pupawere ascertainedfor each concentration of neemarin and for the control. Survival ofimmatures (larva and pupa) was also determined.

2.7. Statistical analysis

The data obtained from all treatments were subjected to oneway analysis of variance (ANOVA) using Minitab-11 for Windows.Mean values were compared using Duncan’s multiple range test(DMRT).

3. Results

3.1. Effect of neemarin on life table and life indices of P. xylostella

Neemarin exhibited a significant (P < 0.05) effect on survivaland development of immature and adult stages of P. xylostella.Survivorship (Ix) increases from 33, 35, 38 and 40 days whenexposed to 5,10,15 and 20mg l�1 as compared to 29 days in control(Fig. 1). Egg hatching was considerably (F4, 14 ¼ 2.68; P ¼ 0.05)affected with increase of concentrations from 5 to 20 mg l�1. A totalof 15% unhatched eggs were obtained in the untreated control,while 31% at 20 mg l�1. Mortality (dx) was found to be variable inrelation to concentration of neemarin (Fig. 2). Mortality of 1stinstars was higher (F4, 14 ¼ 1.06; P ¼ 0.05) at 20 mg l�1 than that of15, 10 and 5 mg l�1 and other instars. Pupal mortality was signifi-cantly (F4, 14 ¼ 5.03; P ¼ 0.05) higher at 20 mg l�1 in comparison to

Fig. 1. Effect of various concentrations of neemarin o

15 mg l�1. The life expectancy (ex) decreases with advancing age inboth exposed and unexposed individuals (Fig. 3).

The life indices of P. xylostella varied significantly (P < 0.05) inexposed and unexposed individuals (Table 1). Females ofP. xylostella started laying eggs 1-day after emergence and the peakoccurred on day 3, then decreased with advancing age in bothexposed and unexposed females. Unexposed females continued tolay the eggs for up to 9 days while for 7 days in females exposed to20 mg l�1 of neemarin. Daily fecundity rate (mx) was significantly(F4, 14 ¼ 0.03; P¼ 0.05) greater (31 offspring/day) than 13 offspring/day when treated with 20 mg l�1 (Fig. 4). Oviposition period wasreduced to 6 days when treated with 20 mg l�1 at 8 days in theuntreated control. However, post oviposition period was 2 days inboth exposed and unexposed individuals. Untreated femalessignificantly (F4, 14 ¼13.85; P¼ 0.05) lived longer (11 days) than thefemales (9 days) when exposed to 20mg l�1. Potential fecundity (Pf)was significantly lower (34 females/female/generation) at20 mg l�1 as compared to the control (92 females/female/genera-tion) (F4, 14 ¼ 0.07; P ¼ 0.05). Reproduction rates (R0) were alsogreatly reduced at 20 mg l�1 as compared to 25.18 females/female/generation in the unexposed individuals (F4, 14 ¼ 0.22; P ¼ 0.05).Smallest intrinsic rate of increase (rm) occurred at 20 mg l�1 andhighest (0.049 females/female/day) in the untreated control (F4,14 ¼ 26.00; P ¼ 0.05). 1.111 females/female/day produced by theunexposed P. xylostella and considerably lower birth (1.024 females/female/day) was observed by exposure at 20 mg l�1 (F4, 14 ¼ 2.29;P¼ 0.05). P. xylostella can be able to complete one generation (Tc) in33.98 days under the influence of 20 mg l�1 of neemarin and 21.07days required in the control (F4, 14 ¼ 1.79; P ¼ 0.05). Correctedgeneration (s) was significantly prolonged to 39.50 days at20 mg l�1 and decreased down gradually at 15, 10, 5 mg l�1 ofneemarin (F4, 14 ¼ 2.73; P ¼ 0.05). P. xylostella was multiplied tobecome double in 6.12 days in untreated control and significantlydelayed to 28.42 days at 20 mg l�1 (F4, 14 ¼ 1.65; P ¼ 0.05).

3.2. Effect of neemarin on development and survival of P. xylostella

Development of immature stage of P. xylostellawas significantly(P < 0.05) prolonged to 32 days at 20 mg l�1 of neemarin ascompared to 18.60 days in the untreated control (Table 2). Incu-bation period is significantly (F4, 14 ¼ 12.74; P ¼ 0.05) delayed to5.09 days at 20 mg l�1 while, 3.02 days in the untreated control andsignificantly differed at 15,10 and 5mg l�1. Larval development wascompleted in 19.07 days at 20 mg l�1. This value was significantly

n survivorship of various stages of P. xylostella.

Fig. 2. Effect of various concentrations of neemarin on mortality of P. xylostella through one generation.

N. Ahmad et al. / Crop Protection 38 (2012) 7e1410

greater than those which were found at 5 mg l�1 (14.36 days) andthe control (11.58 days) (F4, 14 ¼ 4.19; P ¼ 0.05). Pupal developmentwas not significant (P > 0.05) at 15, 10 and 5 mg l�1, while differedsignificantly at 20 mg l�1 and the untreated control. Survival ofimmature stages (larva and pupa) were significantly (P < 0.05)reduced at 20mg l�1 as compared to control (Table 3). A substantialreduction in survival of immature was also observed at 5, 10 and15 mg l�1. Survival of early instars was significantly lowest at20 mg l�1 and the highest at 5 mg l�1 and the control (F4, 14 ¼ 0.08;P ¼ 0.05). Emergence of adult was significantly (F4, 14 ¼ 16.06;P ¼ 0.05) affected by neemarin and considerably reduced at20 mg l�1 as compared to unexposed population.

4. Discussion

Neemarin significantly affected the immature and adult stagesof P. xylostella. Survivorship increases with increase of concentra-tions from 5, 10, 15 and 20 mg l�1 in the present study. However,survivorship of nymphs and adults of Acyrthosiphon pisum (Harris)treated with Morgosan-O was reduced in a concentration depen-dent manner (Stark and Wennergren, 1995). Maximum survivor-ship of adults was 23 days at 100 mg l�1 as compared to 32 day incontrol. They also reported that survivorship of exposed adult was

Fig. 3. Effect of various concentrations of neemarin on lif

reduced; reduction was much less than individuals exposed asyoung. Reduction in survivorship is also obtained by Lashkari et al.(2007) on Brevicoryne brassicae (Linn.) by imidacloprid, Ansari et al.(2008) on P. xylostella by imidacloprid, Yin et al. (2009) onP. xylostella by spinosad, Santos et al. (2004) on Aphis gossypei byneem and neem seed extract, respectively.

In the present study, egg hatch was considerably decreased to31% at 20 mg l�1 of neemarin as compared to 15% in the unexposedcontrol. While, sub lethal concentrations of indoxacarb had nosignificant effect on the hatchability of eggs of P. xylostella(Mahmoudvand et al., 2011a). It may have been due to inappro-priate incorporation of yolk so that the embryo failed to completethe development phase (Kaur et al., 1993). However, Kumar andChapman (1984) suggested that reduction in hatching may bedue to inability to the embryos to perforate surrounding vitellinemembrane, and probably due to weakened chitinous mouth hookassembly required for hatching (Wilson and Cryan, 1997).

Mortality of larval and pupal stages was variable in relation toconcentration and higher at 20 mg l�1 of neemarin than to otherconcentrations tested and in the untreated control. Highestmortality occurred at 1st instar as compared to other instars.Similarly, Stark and Wennergren (1995) found a concentrationdependent death rate where A. pisum was treated with Morgosan-

e expectancy of P. xylostella through one generation.

Table 1Effect of various concentrations of neemarin on the life indices of immature stages of P. xylostella.

Conc. (mg l�1) Pf R0 rm l Tc s DT

Mean SE Mean SE Mean SE Mean SE Mean SE Mean SE Mean SE

20 34 1.56e 2.62 0.057e 0.010 5.77e-4e 1.024 0.012b 33.98 1.16a 39.50 1.44a 28.42 1.183a

15 45 1.84d 4.88 0.096d 0.018 6.89e-4d 1.043 0.020b 31.90 1.09a 37.50 1.35a 16.39 0.931b

10 53 2.05c 6.72 0.107c 0.024 7.67e-4c 1.056 0.028b 27.94 1.02b 34.50 1.29b 12.55 0.748c

5 66 2.33b 10.33 0.216b 0.031 8.84e-4b 1.074 0.037b 24.95 0.987b 32.50 1.16b 9.64 0.523c

Control 92 2.87a 25.18 0.864a 0.049 9.96e-4a 1.111 0.041a 21.07 0.916c 28.50 1.05c 6.12 0.416d

Within column, means followed by different letters are significantly different according to Duncan’s multiple range tests (P < 0.05).

N. Ahmad et al. / Crop Protection 38 (2012) 7e14 11

O. Jaglan et al. (1997) observed a progressive increase in themortality and life period of Helicoverpa armigera (Hubner) larvaewith the increase in concentration of neem extracts. However,Liang et al. (2003) observed that the larvae died slowly by appli-cation of neem insecticides. Rezaei et al. (2007) also showed thatmortality caused by pesticides was significantly different from thecontrol. Kraiss and Cullen (2008) found that azadirachtin and neemseed oil significantly increased the nymphal mortality (80 and 77%respectively) and increased the development time of survivingadults of Aphis glycines (Glover).

Survival of immatures was high in unexposed individuals ascompared to neemarin exposed P. xylostella in the present study.Survival of 1st instars was more affected than other instars at20 mg l�1 of neemarin. Identical result obtained by Weathersbeeand Tang (2002) who showed that survival rate of Diaprepesabbreviatus larvae were reduced after ingesting neemix treated

Fig. 4. Effect of various concentrations of neemarin on natal

foodmost notably among those exposed as neonates. Developmentof immature stages was considerably affected by neemarin in thepresent study. Duration of development of immature was signifi-cantly prolonged at 20 mg l�1 of neemarin and decreased corre-spondingly with concentration. Similar observations were reportedby Charleston (2004) who found that the development ofP. xylostella was significantly prolonged when fed on neem treatedplants which resulted in P. xylostella being available to naturalenemies on the treated plants for a longer period. El-Hawary andAbd El-Salam (2008) observed a prolonged development periodwhen nymphal stages of Aphis craccivora (Koch) exposed to nim-becidine treated plants. A contrary result was obtained by Seljasenand Meadow (2006) who observed depressed development oflarvae in Mamestra brassicae (Linn.) treated with neem extract, asthey failed to develop from 1st to 2nd instars and died after 14 days.Survival rate of pre-adult stages of P. xylostella declined significantly

ity rate (mx) and female survivorship (lx) of P. xylostella.

Table 2Effect of various concentrations of neemarin on the developmental time of immature stages of P. xylostella.

Conc. (mg l�1) Development (days)

Egg incubation I instar II instar III instar IV instar Prepupa Pupa Total

Mean SE Mean SE Mean SE Mean SE Mean SE Mean SE Mean SE Mean SE

20 5.09 0.289a 3.91 0.230a 5.13 0.346a 4.17 0.276a 5.86 0.327a 1.32 0.064a 6.68 0.358a 32.16 1.23a

15 4.18 0.231b 3.57 0.202a 4.64 0.289a 4.02 0.224b 5.47 0.281b 1.23 0.041a 6.26 0.331b 29.37 1.15b

10 3.43 0.173c 3.16 0.170b 3.75 0.206b 3.87 0.198c 5.16 0.239c 1.11 0.032a 5.69 0.246b 26.17 1.06b

5 3.14 0.158d 2.91 0.115c 3.18 0.175c 3.59 0.136d 4.68 0.187d 0.94 0.020a 5.07 0.214b 23.51 0.927b

Control 3.02 0.118d 2.57 0.087c 2.79 0.114c 2.94 0.098e 3.28 0.113e 0.76 0.014a 3.21 0.109c 18.57 0.627c

Within column, means followed by different letters are significantly different according to Duncan’s multiple range tests (P < 0.05).

N. Ahmad et al. / Crop Protection 38 (2012) 7e1412

at LC25 concentration of hexaflumuron (Mahmoudvand et al.,2011b).

Fecundity of P. xylostella was reduced in a concentrationdependent manner from 5 to 20 mg l�1 of neemarin in the presentstudy. Karnavar (1987) also reported that azadirachtin affectedovarian development, fecundity and fertility. Fecundity progres-sively decreased with increasing concentrations of azadirachtin(Pineda et al., 2009). Fecundity of the untreated population wassignificantly greater than those exposed to imidacloprid (Lashkariet al., 2007; Ansari et al., 2008). Fecundity of A. glycines wassignificantly affected by application of azadirachtin and neem seedoil (Kraiss and Cullen, 2008). A. pisum exposed to Morgosan-O asneonates underwent a huge decrease in the fecundity rates andbecame zero after exposure to higher than 40 mg l�1. For aphidsexposed as adults, the fecundity was reduced in a concentrationdependent manner and greatly reduced to 20% for an exposure of100 mg l�1 compared with a maximum fecundity of 90% for thecontrol (Stark and Wennergren, 1995). Reduction in fecundity ofP. xylostella was also observed when exposed to sub lethalconcentrations of hexaflumuron and indoxacarb (Mahmoudvandet al., 2011a, 2011b). While, spinosad caused an increased fecun-dity in Orious insidiosus (Linn.) (Elzen, 2001). One possible expla-nation for this finding was that the surviving individualsmaintained high reproductive rates which allowed them tocompensate for the losses and act as reservoirs for future repro-duction (Walthall and Stark, 1996).

Reproduction rate (R0) is significantly reduced with increasingthe concentration of neemarin on P. xylostella in the present study.Mahmoudvand et al. (2011a,b) reported that R0 was greatly reduced(R< 0.05) when P. xylostella exposed to sub lethal concentrations ofindoxacarb and hexaflumuron. Kaur et al. (2001) suggested thatnumber of females per generation (R0) declined as a function ofpesticide concentration and it was confirmed by Stark andWennergren (1995) that number of females per generation (R0)was as a function of pesticide.

The intrinsic rate of increase (rm) is a measure of the ability ofa population to increase exponentially in an unlimited environ-ment. Dixon (1987) has also suggested that the rm provides aneffective summary of an insect’s life history traits. Therefore, Starket al. (2007) have strongly advocated that the mostly usedmeasures of effect in LTREs is the rm because a total measure of the

Table 3Effect of various concentrations of neemarin on the survival rate of various stages of P. x

Conc. (mg l�1) I instar II instar III instar IV

Mean SE Mean SE Mean SE M

20 72.46 1.73c 78.00 2.47b 74.36 2.06b 615 75.68 2.02c 69.64 1.53c 74.36 2.11b 710 76.62 2.30b 77.97 2.38b 73.91 1.96b 75 80.25 2.86a 81.54 2.67a 79.25 2.54a 7Control 81.18 3.01a 79.71 2.52b 80.00 2.71a 7

Within column, means followed by different letters are significantly different according

population-level effect can be determined with one number. Whenrm is zero, the population is stable (unchanging). When the rm ispositive number the population increases exponentially. When rmis negative, the population declines exponentially towards extinc-tion. rm has also been recommended together with toxicityassessment to provide amore accurate estimate of population-leveleffect of toxic compounds (Stark et al., 1997; Walthall and Stark,1996; Forbes and Calow, 1999). Most pesticides have an ability todecrease the intrinsic rate of increase (rm) for some insects(Lashkari et al., 2007). In our study, rm reduced considerably at20 mg l�1 of neemarin. When neonates of A. pisumwere exposed todifferent concentration of Margosan-O, rm was reduced ina concentration dependent manner and become negative at60 mg l�1 of Morgosan-O showing that population would be at theverge of extinction (Stark and Wennergren, 1995). A significantlyreduced rmwas obtained by Imidacloprid for population of A. pisum(Walthall and Stark, 1996) for B. brassicae (Lashkari et al., 2007) andP. xylostella (Ansari et al., 2008). It was also reported by Saber et al.(2004) that the rm for control and neemazal exposed populationswas 0.340 and 0.335 female offspring/female/day, respectivelybecause some of the post emergence life table parameters of adultsof Trichogramma cacoeciae were significantly reduced by theinsecticide treatment. Sub lethal concentrations of indoxacarbsignificantly decreased the rm of P. xylostella (Mahmoudvand et al.,2011a,b,c).

Mean length of generation (Tc) and corrected generation time (s)of P. xylostella was significantly prolonged when exposed to20 mg l�1 of neemarin as compared to unexposed in the presentstudy. The Tc was also decreased as Morgosan-O concentrationincreased and the population of A. pisum exposed from birth wasmore affected than the population exposed as adult (Stark andWennergren, 1995). Doubling time of populations may reflect onincrease in the time it took for survivors to compensate for loss ofindividual. Doubling time of P. xylostella was prolonged to 28.42days at 20 mg l�1 of neemarin as compared to 6.12 days in unex-posed population. Population of B. brassicae exposed to imidaclo-prid had more time to compensate for lost of individuals (Lashkariet al., 2007) and same result reported by Ansari et al. (2008) onP. xylostella by application of imidacloprid and Mahmoudvand et al.(2011a,b) on P. xylostella by sub lethal concentrations of hexa-flumuron and indoxacarb.

ylostella.

instar Prepupa Pupa Adult

ean SE Mean SE Mean SE Mean SE

8.97 1.79c 85.00 2.81c 47.06 1.16d 8.0 0.431d

5.86 2.17b 90.91 2.94b 55.00 1.24c 11.0 0.745c

0.59 1.98c 91.67 2.99b 59.09 1.38b 13.0 0.924c

8.57 2.32b 84.85 2.74c 57.14 1.28c 16.0 1.13b

9.55 2.44a 97.14 2.86a 85.29 2.58a 29.0 1.48a

to Duncan’s multiple range tests (P < 0.05).

N. Ahmad et al. / Crop Protection 38 (2012) 7e14 13

It is concluded that application of neemarin has increased themortality of larval and pupal stages and considerably affected theemergence of adult as well as significantly reduced the fecundity,reproduction rate and intrinsic rate of increase of P. xylostella.Survival, development time and generation time is prolonged thusthe larvae and pupae of P. xylostella will be made available tonatural enemies for longer time, when cauliflower is treated withneemarin. Therefore, It may be incorporated in the integratedmanagement of P. xylostella on cauliflower because neem basedinsecticides have been found to have little impact on beneficialparasites and predators of P. xylostella (Walter, 1999; Charleston,2004).

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