Leaf-dip Bioassay Research Articles

Bioassay Evaluation of Closer SC for Control of Harlequin Bug and Kudzu Bug, 2013: Table 1

The new sulfoximine insecticide Closer SC (sulfoxaflor) has demonstrated a high level of activity against sucking insects such as aphids and whiteflies, but there is considerably less known about the activity of this insecticide on heteropteran pests. The objective of this experiment was to evaluate the toxicity of sulfoxaflor against two heteropteran pests of agricultural importance, harlequin bug (HB), and kudzu bug (KB). Leaf-dip bioassays were conducted at Virginia Tech in Blacksburg, VA during the summer and fall of 2013. Insecticide solutions were prepared with …

Monitoring of insecticide resistance in Spodoptera litura (Lepidoptera: Noctuidae) from four districts of Punjab, Pakistan to conventional and new chemistry insecticides

Studies were carried out to evaluate the resistance of Pakistani populations of the beet armyworm, Spodoptera litura (F) to several commonly used insecticides. Different field populations of S. litura from four districts of the Punjab were monitored from 2009 to 2011 for resistance to insecticides using a standard leaf dip bioassay method. For organophosphates and pyrethroids, resistance ratios compared with a susceptible Lab-Pk population were in the range of 8–109 fold for deltamethrin, 11–139 fold for cypermethrin, 19–143 fold for chlorpyrifos and 39–162 fold for profenofos. For new chemistry insecticides, resistance levels were 2–74 fold for spinosad, 4–216 fold for abamectin, 7–87 fold for indoxacarb, 2–77 fold for emamectin benzoate, 1.9–58 fold for lufenuron and 4–43 fold for methoxyfenozide. Pairwise correlation coefficients of LC50 values showed a positive correlation with cross-resistance among deltamethrin, cypermethrin and chlorpyrifos, while resistance to profenofos showed correlations with resistances to other insecticides except chlorpyrifos. New chemistry insecticides showed no correlations between any of the tested insecticides. There were high to very high levels of resistance to organophosphates in most of the population, which suggested that the use of these should be avoided against this pest. Selective use of pyrethroids in several areas, including Bahawalpur and Lodhran, where the pest showed a low level of resistance, would appear to be acceptable, the new chemistry insecticides, lufenuron, methoxyfenozide, emamectin and indoxacarb had no, very low, low and moderate resistance levels against populations, respectively. These are considered to be safe to the environment and safer to natural enemies.

Evaluation of Sublethal Effects of Sulfoxaflor on the Green Peach Aphid (Hemiptera: Aphididae) Using Life Table Parameters.

The green peach aphid, Myzus persicae (Sulzer), is an important insect pest of many crops around the world. Pesticide-induced hormesis may be an alternative mechanism for pest resurgence. In this study, life table parameters were applied to the estimation of sulfoxaflor-induced hormesis of adult M. persicae following 2-d LC25 concentration exposure. Leaf-dip bioassays showed that the sulfoxaflor possessed high toxicity against M. persicae, with an LC50 of 0.059 mg/liter. The results indicated that the exposure of the parent generation of M. persicae to sublethal sulfoxaflor induced increase in reproduction and prolongation of immature development duration in the first progeny generation. Both R0 and GRR of aphids for treatment group were significantly higher than for the control in F1 generation, and the mean generation time was significantly postponed in treated group. These results suggest a hormesis induced by lower concentration of sulfoxaflor in M. persicae. It would be useful for assessing the overall effects of sulfoxaflor on M. persicae.

Monitoring of Resistance to New Chemistry Insecticides in Spodoptera litura (Lepidoptera: Noctuidae) in Pakistan.

The armyworm Spodoptera litura (F.) is a very serious pest of many crops, vegetables, and ornamentals. Due to persistent application of insecticides, this pest has developed resistance to conventional as well as new chemistries. The present studies investigated the level of resistance to new chemistry insecticides, having novel modes of action, in the Pakistani field populations of S. litura during 1997-2010 by using a leaf-dip bioassay. Generally, a low to moderate resistance was recorded to indoxacarb, abamectin, fipronil, and methoxyfenozide; along with a very low resistance to spinosad. Resistance to emamectin benzoate, chlorfenapyr, and lufenuron was none or very low, in spite of their intensive use against S. litura. The insecticides, showing no or very low resistance, can be used in rotation in conjunction with other integrated pest management tactics to manage insecticide resistance in S. litura.

Field resistance of Spodoptera litura (lepidoptera : noctuidae) to newer chemistry insecticide indoxicarb in Vidarbha

The present studies were carried out to evaluate resistance in the population of Spodoptera litura Fab. (Lepidoptera, Noctuidae) from eight districts of Vidarbha region in India to indoxicarb from 2011-2013 using standard leaf dip bioassay method. For indoxicarb, resistance ratio compared with a susceptible strain were in range of 2.66 to 6.14 fold. However, relatively low level of resistance to indoxicarb was observed in all eight populations.

Studies on time-mortality response of diamondback moth, Plutela xylostella L. larvae to different insecticides and in combination with streptocycline

The toxicity of insecticides with bactericide and individual insecticides to test insect was quantified by adopting leaf dip bioassay method and the compatibility was assessed based on the median lethal concentrations(LC 50 ). The results clearly revealed that in some combinations toxicity was enhanced while in others the toxicity was lowered. Among seven insecticides in combination with bactericide, streptocycline tested for efficacy, four insecticides (chlorantraniliprole, flubendiamide, Proton and profenophos) showed synergistic effect (SF 1.18, 1.07, 1.03 and 1.01, respectively), whereas three insecticides (indoxcarb, novaluron and Hamla) were antagonistic (SF 0.83, 0.89 and 0.93, respectively) against P. xylostella larvae. How to view point the article : Siddartha, D, Revannavar, Revanna and Somu, R. (2014). Studies on dosage-mortality response of diamondback moth, Plutelaxylostella L. larvae to different insecticides and in combination with Streptocycline. Internat. J. Plant Protec., 7(2) : 354-359.

Bioefficacy of three insecticides against tobacco caterpillar,Spodoptera litura(Fab.)

The bioefficacy of three insecticides viz. monocrotophos, indoxacarb, and chlorpyriphos was determined against 9 day old larvae of Spodoptera litura by leaf dip bioassay method. The mortality data recorded at 18, 24, 36, 48 and 72 hours after exposure (HAE) did not meet the basic requirements to go for probit analysis, therefore LC values have not been computed at these exposure periods for indoxacarb. At 24 HAE, the LC50 values of monocrotophos & chlorpyriphos were 220 & 170 ppm respectively. Chlorpyriphos showed 1.29 times more toxicity than monocrotophos at LC50 while at 34 HAE, monocrotophos showed 1.11 times more toxicity than chlorpyriphos against S. litura. In leaf dip bioassay, indoxacarb could cause 50% mortality in a shortest span of 16.64 h at 50 ppm followed by chlorpyriphos (18.06 h) at 400 ppm and monocrotophos (30.39 h) at 200 ppm.

Effects of Pyriproxyfen on Life Table Indices ofPlutella xylostellain Multigenerations

The diamondback moth (DBM),Plutella xylostella(L.) (Lepidoptera: Plutellidae), is a major pest of Brassicaceae family in Iran. This study investigated the sublethal effects of pyriproxyfen, a juvenile hormone analogue, on DBM, for two subsequent generations. The leaf dip bioassay method was adopted in conducting this experiment. Sublethal concentrations resulted in a significant decrease in fecundity, oviposition period, and pupal weight of parents and offspring generations. Also, the development time of DBM was prolonged after exposure to pyriproxyfen. The biological parameters such as net reproductive rate (R0) and intrinsic (rm) and finite (λ) rate of increase were lower than control in treatment groups, significantly. From our investigations, pyriproxyfen is a good choice for control of the diamondback moth population through continuous generations.

Studies on dosage-mortality response of diamondback moth, Plutelaxylostella L. larvae to different insecticides in combination with Streptocycli

The toxicity of insecticides with bactericide and individual insecticides to test insect was quantified by adopting leaf dip bioassay method and the compatibility was assessed based on the median lethal concentrations(LC50). The results clearly revealed that in some combinations toxicity was enhanced while in others the toxicity was lowered. Among seven insecticides in combination with bactericide, streptocycline tested for efficacy, four insecticides (chlorantraniliprole, flubendiamide, Proton® and profenophos) showed synergistic effect (SF 1.18, 1.07, 1.03 and 1.01, respectively), whereas three insecticides (indoxcarb, novaluron and Hamla®) were antagonistic (SF 0.83, 0.89 and 0.93, respectively) against P. xylostella larvae.

EVALUATION OF TOXICITY AND COTOXICITY OF BIOPESTICIDES AGAINSTDIAMONDBACK MOTH, PLUTELLA XYLOSTELLA (L.)

ABSTRACT In India, the diamondback moth, Plutella xylostella (L.) (Lepidoptera: Plutellidae), is an important pest of cruciferous vegetables and causes severe economic losses. This pest has ability to evolveresistance in laboratory and field to almost all groups of synthetic insecticides. Despite of these, management with synthetic insecticides has been considered to be the easy and favorable option byfarmers in India which indeed increase the cost of cultivation and obviously reduction in the actual net profit. The use of microbial and botanicals pesticides are also available in the market and theyare relatively cheap. These pesticides are eco-friendly and the residual toxicity is extremely low. Inthis study, we have evaluated the in vitro toxicity and co-toxicity of different groups of microbial and botanicals pesticides on the field derived population of P. xylostella using leaf dip bioassay. Among microbial pesticides Lipe (Bacillus thuringiensis subsp. kurstaki)) was found to be veryeffective than MVP II (Cry1Ac) and XenTari® (Bacillus thuringiensis subsp. aizawai). Anosom®(1% EC) was found to be most effective against P. xylostella among botanicals as evidenced fromlowest LC50 value of only 0.1ppm. Being a botanical pesticide, Anosom® (1% EC) could be usedas a substitute to synthetic insecticides in integrated management of P. xylostella. Co-toxicity of pesticides against second instars larvae of P. xylostella was assessed using binary mixture of twobotanical pesticides at three different combinations (1:1, 1:2 and 2:1 ratio) and found that all thecombinations show synergistic effect against diamondback moth. Objective of present research is toinvestigate toxicity and co-toxicity of botanical and microbial pesticides against diamondback mothso that it could be used as substitute to chemical pesticide for integrated management of diamondback moth.

Laboratory evaluation of toxicity of <i>Bacillus thuringiensis</i>, neem oil and methamidophos against <i>Plutella xylostella</i> L. (Lepidoptera: Plutellidae) larvae

Diamondback moth (DBM), Plutella xylostella (L.), remains a major pest of brassica crops worldwide. Chemical control of this pest remains difficult due to the rapid development of resistance to insecticides and to their effect on natural enemies. The objective of this study was to assess the toxicity of Bacillus thuringiensis (Bt), neem oil and methamidophos on larvae of P. xylostella under laboratory conditions. Leaf-dip bioassay for DBM larvae was used to assess mortality. For each treatment, three doses (low, medium and high) were applied on cabbage leaves and presented to third instar larvae. Larval mortality was performed every 24 hours for a period of eight days. The application of the three dosages of Biobit was more effective against P. xylostella larvae when compared to the other treatments. However, there was no significant difference in larval mortality when all three doses of Biobit were tested compared to the control. Methamidophos was the least toxic treatments with high dosage recording the lowest mortality rate of 52.5%. These results showed that Btbased biopesticides and neem extracts could be of help, but their deployment should be part of an integrated pest management package, which recognizes the constraints of farmers while addressing the requirement to control of P. xylostella populations.Keywords: Diamondback moth, biopesticide, Azadirachta indica, cabbage, bioassay.

Baseline toxicity of chloronicotinyls against cotton leafhopper, Amrasca biguttula biguttula, and detection of insecticide resistance

The populations of cotton leafhopper, Amrasca biguttula biguttula were collected from two different locations, viz. Coimbatore and Salem, and the identified susceptible Salem population was cultured continuously for four generations without exposure to insecticides and the baseline toxicity data were established by leaf dip bioassay method (IRAC method No. 8). The tentative discriminating doses fixed, based on the susceptible A. biguttula biguttula population, were 1.10, 0.10, 0.02 and 1.0 ppm for imidacloprid, thiamethoxam, acetamiprid and thiacloprid, respectively. Insecticide resistance was then monitored using the above doses against leafhoppers collected from Coimbatore, Bhavanisagar, Salem and Srivilliputhur. The level of resistance in A. biguttula biguttula, as revealed by per cent survival, varied from 6.67 (Salem) to 15.38 (Srivilliiputhur) for imidacloprid; 3.33 (Salem) to 15.09 (Srivilliputhur) for thiamethoxam; 5.00 (Bhavanisagar) to 20.00 (Srivilliputhur) for acetamiprid; and 5.00 (Bhavanisagar) to 9.09 (Srivilliputhur) for thiacloprid.

Monitoring Insecticide Resistance in Biotype B ofBemisia tabaci(Hemiptera: Aleyrodidae) in Florida

Biotype B of the sweetpotato whitefly (SPWF), Bemisia tabaci (Gennadius) (also known as the silverleaf whitefly, B. argentifolii Bellows & Perring), is the key pest of tomatoes in south Florida, primarily as a vector of the begomovirus Tomato yellow leaf curl virus (TYLCV). Insecticides are most often used to manage the SPWF and TYLCV. A resistance monitoring program that was initiated in Florida in 2000 was continued from 2008 to 2010 and included 4 neonicotinoid insecticides (imidacloprid, thiamethoxam, dinotefuran, and acetamiprid), the insect growth regulator buprofezin, the pyrethroid bifenthrin, and the organochlorine endosulfan. Ten field populations in 2008 and 9 each in 2009 and 2010 were established with nymphal infested foliage and were tested for susceptibility using a systemic uptake, cut-leaf petiole bioassay with adults for the neonicotinoids; a leaf-dip bioassay with 2nd instars for buprofezin; and a vial bioassay with adults for bifenthrin and endosulfan. Each field population was exposed to the LC50 and LC95 of a known susceptible laboratory colony for each respective insecticide and mortality was compared with that at the same doses predicted from probit analyses of field populations tested in 2007. T-tests were used to determine the significance of differences between the mean mortality at the LC values of each field collected colony compared to the respective LC values of the laboratory susceptible strain. T-tests were also used to determine the significance of differences between the mean of the predicted mortality at the LC values of field collected populations in 2007 and the means of the LC values of field collected populations in 2008–2010 for each insecticide. Results indicated that, based on mortality averaged over all populations evaluated, all of the neonicotinoids indicated decreases in average susceptibility in 2008 and 2009 compared with the 2007 values, although the differences were less for dinotefuran and acetamiprid. The lowest average of mortality at both the LC50 and LC95 in 2008 and 2009 occurred for imidacloprid and thiamethoxam. These neonicotinoids had been in use longer than either of the other two. Mortality values for bifenthrin suggested an overall increase in field susceptibility in 2008 and 2009 while values for endosulfan suggested no change. There were no data predicted for buprofezin in 2007, but the 2008 average mortalities at the LC50 and LC95 were 0.438 and 0.802, respectively, indicating that field susceptibility was at an acceptable level. In 2010 the average susceptibility to the neonicotinoids appeared to have increased compared with previous years; however, the field populations tended to be evaluated after they had been reared in the laboratory without exposure to insecticides for more generations than in previous years. Despite this, average susceptibility to endosulfan appeared to decrease. The results showed the utility of using predicted LC50 and LC95 values, over the use of full dose range, for monitoring changes in susceptibility in field populations thru time. The data presented here provide important information aid to growers and producers in making decisions on insecticide usage.

Physiological and Population Responses of Armyworm <I>Mythimna separata</I> (Lepidoptera: Noctuidae) to a Sublethal Dose of Cantharidin-AC

The oriental armyworm Mythimna separata Walker is a serious threat to the production of cereals. Its control has largely relied on synthetic insecticides, which led to the decrease in their effectiveness. In China, cantharidin, a natural compound of insect origin with a mode of action different from a conventional insecticide, is being developed as a bio-insecticide for the control of lepidopteran pests. Its toxicological effects have already been studied in M. separata. However, its sublethal effects on physiological and population parameters have not yet been studied. The leaf dip bioassay results showed that cantharidin-AC (cantharidin acetone solution) had a high level of toxicity against M. separata and the 96 h LC50 value was 223 microg/ml. The sublethal effects of cantharidin exposure for 72 h at LC10 (77 microg/ml) on physiological and population parameters of M. sepatata were also investigated, and data were subjected to an age-stage two-sex life-table. The sublethal effects of cantharidin indicated reduction in survival rates of larval, pupal, and adult stages. In addition, both male and female moths were observed with crippled wings in the cantharidin-treated cohort. The mean values of the finite rate of increase (lambda), the intrinsic rate of increase (gamma), and the net reproductive rate (R(o)) were significantly lower in the treatment than in the control. The fecundity was also strongly affected by a sublethal cantharidin concentration. A sublethal concentration of cantharidin may reduce the population growth of M. separata by decreasing its survival and reproduction and by increasing its generation time.

Susceptibility ofMicrotheca ochroloma(Coleoptera: Chrysomelidae) to Botanical and Microbial Insecticide Formulations

ABSTRACT The yellowmargined leaf beetle, Microtheca ochroloma Stal (Coleoptera: Chrysomelidae), is a key pest of organic crucifer production in the southern United States. The susceptibility of larvae and adults of M. ochroloma to some botanical and microbial insecticide formulations was evaluated using laboratory leaf-dip bioassays. Insecticides evaluated included OMRI (Organic Material Review Institute) approved formulations of PyGanic® (pyrethrum), Entrust® (spinosad), Mycotrol O® (Beauveria bassiana strain GHA), and NOFLY® (Isaria fumosoroseus strain FE 9901). Others were MBI-203 (experimental organic formulation of Chromobacterium subtsugae) and BotaniGard® 22WP (conventional formulation of Beauveria bassiana strain GHA). The insecticides were first evaluated at the field recommended rate against M. ochroloma larvae and adults, followed by multiple-concentration assays to determine the LC50 and LT50 for promising formulations. At the field recommended rates, all tested formulations were toxic to the ...

Field resistance of Spodoptera litura (Lepidoptera: Noctuidae) to organophosphates, pyrethroids, carbamates and four newer chemistry insecticides in Hunan, China

The present studies were carried out to evaluate resistance in the populations of Spodoptera litura Fab. (Lepidoptera, Noctuidae) from five districts of Hunan Province in China to various insecticides from 2010 to 2012 using a standard leaf dip bioassay method. For organophosphates and pyrethroids, resistance ratios compared with a susceptible Lab-BJ strain were in the range of 14–229-fold for organophosphates and 12–227-fold for pyrethroids. Similarly, relative low levels of resistance to emamectin, indoxacarb, and chlorfenapyr were observed in all five populations. In contrast, the resistance to carbamates (thiodicarb or methomyl) was significantly higher than that of organophosphates, pyrethroids and newer chemistry insecticides. The pairwise correlation coefficients of LC50 values indicated that the newer chemistry insecticides and old generation insecticides were not significant except abamectin, which was negatively significantly correlated with methomyl. A significant correlation was observed between thiodicarb, methomyl, and deltamethrin, whereas resistance to bifenthrin showed no correlations with resistance to other insecticides except deltamethrin. The results are discussed in relation to integrated pest management for S. litura with special reference to management of field evolved resistance to insecticides.

Induced resistance against the Asian citrus psyllid, Diaphorina citri, by β-aminobutyric acid in citrus

β-Aminobutyric acid (BABA) is known to induce resistance to microbial pathogens, nematodes and insects in several host plant/pest systems. The present study was undertaken to determine whether a similar effect of BABA occurred against the Asian citrus psyllid, Diaphorina citri Kuwayama, in citrus. A 25 mM drench application of BABA significantly reduced the number of eggs/plant as compared with a water control, whereas 200 and 100 mM applications of BABA reduced the numbers of nymphs/plant and adults/plants, respectively. A 5 mM foliar application of BABA significantly reduced the number of adults but not eggs or nymphs when compared with a water control treatment. In addition, leaf-dip bioassays using various concentrations (25–500 mM) of BABA indicated no direct toxic effect on 2nd and 5th instar nymphs or adult D. citri. BABA-treated plants were characterized by significantly lower levels of iron, magnesium, phosphorus, sodium, sulfur and zinc as compared with control plants. The expression level of the PR-2 gene (β-1,3-glucanase) in BABA-treated plants that were also damaged by D. citri adult feeding was significantly higher than in plants exposed to BABA, D. citri feeding alone or control plants. Our results indicate the potential for using BABA as a systemic acquired resistance management tool for D. citri.

Chlorpyrifos ethyl-oxon sensitive and insensitive acetylcholinesterase variants of greenhouse whitefly Trialeurodes vaporariorum (Westw.) (Hemiptera:Aleyrodidae) from Turkey

Resistance to the organophosphate chlorpyrifos ethyl was investigated in greenhouse populations of Trialeurodes vaporariorum from Turkey using both bioassay and biochemical studies. These populations were collected from Antalya, Izmir, and Mersin. LC50 values to chlorpyrifos ethyl were determined for all populations using leaf dip bioassay. Resistance ratios (RRs) were calculated from these LC50 values relative to the susceptible BCP population. Bioassay results from all populations revealed varying levels of resistance to chlorpyrifos ethyl with resistance ratios between 7.16- and 12.89-fold in the greenhouse whitefly populations from Turkey. Results revealed the first documented cases of insecticide resistance in this species in Turkey.Biochemical assays on acetylcholinesterase (AChE) sensitivity in individual greenhouse whitefly were conducted to explore the role of this enzyme in conferring resistance to this insecticide. AChE insensitivity in individual greenhouse whitefly was determined. This is believed to be the first record of sensitive and insensitive AChE variants to be identified according to their sensitivities to chlorpyrifos ethyl-oxon and pirimicarb.

Insecticidal activity of chitosans of different molecular weights and chitosan-metal complexes against cotton leafworm Spodoptera littoralis and oleander aphid Aphis nerii

As an alternative to synthetic pesticides, chitosan has received much attention as a biopolymer active against some agricultural pests. The, insecticidal activity of chitosans of four molecular weights (2.27 × 10<sup>5</sup>,3.60 × 10<sup>5</sup>,5.97 × 10<sup>5</sup>,and9.47 × 10<sup>5 </sup>g/mol) was investigated against two species of arthropod pests: oleander aphid Aphis nerii and cotton leafworm Spodoptera littoralis. In addition, the most active chitosan of 2.27 × 10<sup>5 </sup>g/mol was chemically modified with metals of Ag(I), Cu(II), Ni(II), and Hg(II) to give corresponding chitosan-metal complexes. Larval mortality, growth inhibition, and antifeedant activities for third instar larvae of S. littoralis were evaluated at 4 g (a.i.) chitosan/kg diet. Chitosan of 2.27 × 10<sup>5 </sup>g/mol and its complexes with Ni and Hg were the most active compounds. The results against A. nerii indicated that chitosans of 3.60 × 10<sup>5</sup> and 5.97 × 10<sup>5 </sup>g/mol showed high activity among the different molecular weights in leaf-dip bioassay after 24 h of treatment with 48 and 49% mortalities, respectively, at 1000 mg/l. All compounds had a systemic effect against A. nerii. Chitosans of 2.27 × 10<sup>5</sup>,3.60 × 10<sup>5</sup>,and5.97 × 10<sup>5 </sup>g/mol showed the highest efficacy at all concentrations tested; however, chitosan-Cu was significantly the most active among the complexes.

Residual toxicity and sublethal effects of chlorantraniliprole on Plutella xylostella (Lepidoptera: Plutellidae)

The diamondback moth (DBM), Plutella xylostella (L.), is the most important pest of cruciferous vegetables in the world. Chlorantraniliprole is a novel anthranilic diamide insecticide registered for the control of lepidopteran pests. The dose response, residual toxicity and sublethal effects of chlorantraniliprole applied for 48 h at LC₁₀ (0.02 mg L(-1) ) and LC₂₅ (0.06 mg L(-1) ) on P. xylostella were investigated. Leaf-dip bioassays showed that chlorantraniliprole had a high level of toxicity against larvae of P. xylostella, and the 48 h LC₅₀ values were 0.23 and 0.25 mg L(-1) for a susceptible and field strain respectively. Chlorantraniliprole also had a long-lasting effect when the larvae were exposed to chlorantraniliprole field sprayed on radish seedlings. Sublethal effects of chlorantraniliprole were indicated by reduced pupation, pupal weight and adult emergence rates. There was also an increase in the duration of female preoviposition period, decreased fecundity and egg hatch and decreased survival rates of the offspring. The mean values of the net reproductive rate (R₀), intrinsic rate of increase (r(m)), finite rate of increase (λ) were significantly lower in the treatment than in control groups. These results indicate that chlorantraniliprole is effective against P. xylostella. The sublethal concentrations of chlorantraniliprole may reduce the population growth of P. xylostella by decreasing its survival and reproduction, and by delaying its development.