Life Table Studies Research Articles

Role of Life Table in Insect Pest Management--A Review

Life table study is very useful to analyse the mortality of insect population, to determine key factors responsible for the highest mortality within population. It is determined by two types viz., Age Specific (or Horizontal) and Stage Specific (or Vertical) Life Table. Moreover, various mathematical formulas also indicated for the appropriate evaluation of life fecundity tables, stable age distribution and life expectancy. Life expectancy of beneficial insects can be calculated and used for biological control program by predicting natural things in particular instar within which the maximum mortality of the pests is obtained and plan for managing pests in time.

Natural biological control of green scale (Hemiptera: Coccidae): a field life-table study

Understanding how the biotic and abiotic factors influence pest-population dynamics is important to implement sound pest management strategies in biological control and integrated pest management (IPM) programmes. Coccus viridis (Green) is an important indirect pest of coffee plants, but very little has been done to understand the factors that contribute most for its biological control in the field. In the present study, we examined the critical life stage and the key factors associated with the mortality of C. viridis in coffee plantations in Brazil by conducting field-based life table studies. Predators, parasitoids, fungi, infested leaf abscission and rainfall were collectively responsible for a total C. viridis mortality of 96.08%. Predation by coccinellids was the key factor governing the mortality of C. viridis. The parasitism of early instars by parasitoids was the second most important factor contributing to C. viridis mortality. Unlike the parasitoids, the fungus Lecanicillium lecanii caused mortality of scales in more advanced life stages. The abscission of infested leaves from the trees, and rainfall also contributed to the mortality of C. viridis. The nymph stage was considered the critical stage for mortality of C. viridis in the field. The results suggest that predators (Coccinellidae) are the most important factors controlling C. viridis, and thus should be the target of conservation measures in coffee plantations infested with this pest.

Food stoichiometry affects the outcome of Daphnia–parasite interaction

Phosphorus (P) is an essential nutrient for growth in consumers. P-limitation and parasite infection comprise one of the most common stressor pairs consumers confront in nature. We conducted a life-table study using a Daphnia–microsporidian parasite model, feeding uninfected or infected Daphnia with either P-sufficient or P-limited algae, and assessed the impact of the two stressors on life-history traits of the host. Both infection and P-limitation negatively affected some life-history traits tested. However, under P-limitation, infected animals had higher juvenile growth rate as compared with uninfected animals. All P-limited individuals died before maturation, regardless of infection. The numbers of spore clusters of the microsporidian parasite did not differ in P-limited or P-sufficient hosts. P-limitation, but not infection, decreased body phosphorus content and ingestion rates of Daphnia tested in separate experiments. As parasite spore production did not suffer even under extreme P-limitation, our results suggest that parasite was less limited by P than the host. We discuss possible interpretations concerning the stoichiometrical demands of parasite and suggest that our results are explained by parasite-driven changes in carbon (C) allocation of the hosts. We conclude that the impact of nutrient starvation and parasite infection on consumers depends not only on the stoichiometric demands of host but also those of the parasite.

Article Retraction

The paper, ‘Life Table Studies of Elasmopalpus lignosellus (Lepidoptera: Pyralidae) on Sugarcane,’ by Hardev S. Sandhu, Gregg S. Nuessly, Susan E. Webb, Ronald H. Cherry, and Robert A. Gilbert, Environmental Entomology (2010) 39(6): 2025–2032, is withdrawn at the request of the authors due to numerous errors that cannot readily be corrected by publishing an erratum. I acknowledge the valuable input of Prof. Hsin Chi, Department of Entomology, National Chung Hsing University, Taichung, Taiwan, in raising significant questions about the published paper. — E. Alan Cameron, Editor-in-Chief

Stage-specific mortality, fecundity, and population changes in Cassida rubiginosa (Coleoptera: Chrysomelidae) on wild thistle

Cassida rubiginosa Müller (Coleoptera: Chrysomelidae), one of the most conspicuous defoliators of thistle weeds, is capable of severely damaging thistle leaves; however, populations rarely reach sufficient density for effective thistle control under natural conditions. To investigate the impact of natural mortality factors on C. rubiginosa populations, life table studies were conducted between 1996 and 1998 in Kanazawa, Japan. Egg mortality, mortality in early larvae, and lost fertility contributed strongly to total generational mortality in every year studied. Egg mortality was primarily attributable to parasitism by wasps of the genus Anaphes, and the impact of predation and egg inviability was small. Mortality factors that affected the larval and pupal stages were largely unknown. Under field conditions, females only realized approximately 8.1–13.7 % of their potential fecundity, varying from 36.0 to 61.4 eggs per individual. Since annual changes in lost fertility exhibited a similar pattern to those in generational mortality, fertility loss might be the key factor driving C. rubiginosa populations. These results suggest that reproduction is the most important process that determines the level and fluctuation of the C. rubiginosa population.

A Comparison of Artificial Diet and Hybrid Sweet Corn for the Rearing of Helicoverpa armigera (Hübner) (Lepidoptera: Noctuidae) Based on Life Table Characteristics

The demographic characteristics of Helicoverpa armigera (Hübner) reared on hybrid sweet corn (Zea mays L. variety saccharata) (hybrid super sweet corn KY bright jean) and on an artificial diet were compared by using the age-stage, two-sex life table. Because the hatch rate of eggs varies with maternal age, age-specific fecundity was calculated based on the numbers of hatched eggs to reveal the biological characteristics of H. armigera accurately. The intrinsic rate of increase (r), finite rate (λ) and mean generation time (T) of H. armigera were 0.0853 d(-1), 1.0890 d(-1), and 46.6 d, respectively, on Z. mays and 0.1015 d(-1), 1.1068 d(-1), and 46.3 d, respectively, on the artificial diet. There were significant differences in the intrinsic rate of increase and finite rate between two treatments. The age-stage life expectancy and reproductive value also were calculated. The relationships among the net reproductive rate, the mean female fecundity, the number of emerged females, and the total number of individuals used in the life table study are consistent with theoretical expectations. We recommend the age-stage, two-sex life table for use in insect demographic studies to incorporate both sexes and the variation in developmental rate among individuals and to obtain accurate population parameters. The artificial diet is more suitable for the mass rearing of H. armigera.

Effects of host plants on distribution, abundance, developmental time and life table parameters of Oligonychus afrasiaticus (McGregor) (Acari: Tetranychidae)

The biology and ecology of the date palm mite O. afrasiaticus have been studied through regular inspection in Tunisian oases and laboratory observations. Results indicate that the start date of fruit infestation varied between years and by date palm variety. Start dates ranged from the first week to the third week of July. The period spent by the mite on fruits varied from one variety to another; lasting 8 weeks on the Deglet Noor variety, 2 to 5 weeks on Alig, 2 to 4 weeks on Kentichi dates, and 2 to 4 weeks on Bessr fruits. The Deglet Noor variety was the most susceptible to O. afrasiaticus. Mite populations on the pinnae remained low from May through December. During autumn and spring, O. afrasiaticus was found on sorghum leaves in the orchard ground-cover. A life table study in the laboratory at 27°C on six host plants (fruits of date palms varieties Deglet Noor, Alig, Kentichi, Bessr, and Deglet Noor pinnae and sorghum leaves) showed that the life cycle of O. afrasiaticus differed among host plants with average values ranging between 13 on Alig fruits and 10.9 days on sorghum leaves. Relatively high fecundity was found on sorghum leaves (2 eggs/female/day) during 5.2 oviposition days, while low fecundity values occurred on Deglet Noor pinnae and Alig fruits with 0.7 eggs/female/day during 5.4 days. Average longevity of O. afrasiaticus females ranged from 13.4 to 7.5 days on Deglet Noor fruits and sorghum leaves, respectively. Intrinsic rate of increase (r m) was highest on sorghum leaves (0.171) and Deglet Noor fruits (0.166), and lowest on Alig fruits (0.103). Greater knowledge of life history traits and seasonal abundance of this species is needed in order to design appropriate control strategies.

Impacts of transgenic Bt cotton on a non-target pest, Apolygus lucorum (Meyer-Dür) (Hemiptera: Miridae), in northern China

Transgenic Bt ( Bacillus thuringiensis) cotton has been effectively used to control the cotton bollworm, Helicoverpa armigera (Hübner) in China. However, in recent years, following the wide commercialization of Bt cotton in northern China there have been frequent outbreaks of the non-target pest Apolygus lucorum (Meyer-Dür). To clarify how transgenic cotton contributes to these outbreaks, a four-year field investigation of population dynamics and laboratory life table studies were carried out from 2007 to 2010 to evaluate the impact of two transgenic cotton cultivars (SGK321 expressing Cry1Ac + CpTI and GK12 expressing Cry1Ac) and their corresponding parental non-transgenic lines (Shiyuan321 and Simian3) on A. lucorum. There were no significant differences in the population densities of A. lucorum found in Bt cotton and non-Bt cotton plots, whether one compared those that had received insecticide treatments or those that had not. However, population densities of A. lucorum were significantly lower in pesticide treated plots than in controls. Furthermore, there were no significant differences in the net reproductive rates, generation times or intrinsic rates of increase of A. lucorum when reared on either Bt or non-Bt cotton cultivars. These results suggest that Bt cotton has no direct positive or negative effects on the biology of A. lucorum, so the most logical explanation for the observed outbreaks is the decrease in pesticide applications following the commercial release of Bt cotton.

Effect of fenvalerate on the reproduction and fitness costs of the brown planthopper, Nilaparvata lugens and its resistance mechanism

The brown planthopper (BPH), Nilaparvata lugens Stål, is a primary insect pest of cultivated rice, and its effective control is essential for crop production. However, in recent years, outbreaks of the brown planthopper have occurred more frequently in China. In order to determine the causes and mechanisms of insecticide-induced BPH resurgence and perform population management, we conducted the following studies. By the topical application method, our results showed that, fenvalerate acted as stimulus of fecundity from 3.50 × 10 −3 to 2.02 × 10 −2 μg/female in the BPH. Apart from 7.00 × 10 −3 μg/female, the number of hatched nymphs was increased gradually with an increase in application dose from 3.50 × 10 −3 to 1.74 × 10 −2 μg/female. After continuous selection with fenvalerate for 11 generations by the rice-stem dipping method, a resistant strain was achieved with medium resistance to fenvalerate (RR 39.22). Life table study indicated that the resistant strain (G4 and G8) showed reproductive advantages, including increased female ratio, copulation rate and fecundity. But the hatchability of resistant strain was lower. The survival rate and emergence rate were significantly lower in G4 and G8 resistant strain. Resistant strains in G4 and G8 showed a fitness advantage (1.04 and 1.11), and the number of offspring in G8 generation was higher than that in G4 generation. The significant difference detected between resistant insects (G4, G5, G8 and G9) and S-strain contains not only the effect of resistant selection but also the effect of continuous rearing itself. Hence it was concluded that the BPH had the potential to develop high resistance against fenvalerate and the induction of the nymphs by sublethal doses of fenvalerate was of importance in the BPH population management, particularly in the predicting. Further studies demonstrated that triphenyl phosphate (TPP) and diethyl maleate (DEM) had no synergism on fenvalerate. However, piperonyl butoxide (PBO) displayed significant synergism in susceptible strain (1.97) and resistant strain (2.73). We concluded that esterase and glutathione S-transferase play little role in fenvalerate detoxification. The increase of the P450-monooxygenases detoxification is an important mechanism for fenvalerate resistance. Because their resistant populations had a fitness advantage, we should pay close attention to the occurrence of BPH and use other functionally different insecticides to control the BPH.

Two-sex life table and predation rate of Cybocephalus flavocapitis Smith (Coleoptera: Cybocephalidae) reared on Aulacaspis yasumatsui Takagi (Hemiptera: Diaspididae), in Taiwan

Development, survival, and fecundity of the predator, Cybocephalus flavocapitis Smith, reared on its host Aulacaspis yasumatsui Takagi, were studied at 24 °C, 70 ± 10% RH, and photoperiod of 12:12 (L:D) h under laboratory conditions. Developmental periods for egg, larval, and pupal stages were 6.4, 12.1 and 14.3 d, respectively. The mean longevity of adults was 85.1 d. Raw life history data of all individuals were pooled and analyzed according to the age-stage, two-sex life table theory. The intrinsic rate of increase ( r) was 0.05 d − 1 , the finite rate of increase ( λ) was 1.05 d − 1 , the net reproductive rate ( R 0) was 29.1 offspring, and the mean generation time ( T) was 63.3 d. When we incorporated the age-stage variability of predation rate with the two-sex life table, our results indicated that the predation rates of larvae and adults were 743 eggs and 1595 scales, respectively. The net predation rate of C. flavocapitis is 1874 scales. Additionally, we compared life table results of C. flavocapitis with those of a previous life table study on Cybocephalus nipponicus because both species are currently used for the biological control of A. yasumatsui in Taiwan.

Providing insights into browntail moth local outbreaks by combining life table data and semi-parametric statistics

1. Life table studies have been an essential tool for the comprehension of insect population dynamics, although their use has been methodologically biased by a primary focus on mortality factors, especially natural enemies. Thus, studies in natural populations may relegate important mortality sources to the ‘unknown’ or ‘residual’ mortality categories. To overcome this limitation, life tables may be complemented by combining them with other approaches. 2. The aim of the present study was to provide insights into browntail moth Euproctis chrysorrhoea L. (Lepidoptera: Lymantriidae) local outbreaks by combining life table data and statistical modelling. First, E. chrysorrhoea population density, mortality dynamics, net reproductive rate, and reproductive potential were compared in two different Mediterranean habitats (i.e. coastal and inland). Second, we investigated the relationship of reproductive potential as well as residual mortality (i.e. not associated to any specific mortality agent) with several variables likely to play an important role in E. chrysorrhoea population dynamics. As an innovative approach, the relationship was modelled by means of generalised additive modelling (GAM models) in a multi-model inference framework. 3. The present results on E. chrysorrhoea density and life table analyses suggest that local outbreaks are more likely in coastal habitats where higher mortality was compensated by higher reproductive potential. GAMs turned out to be an effective way to gain a deep understanding of this pattern. Residual mortality was positively and non-linearly related to population density, whereas reproductive potential was not significantly related to any of the variables studied. 4. The present study was an attempt to gain a deep understanding of the information derived from descriptive life tables.

Preference and performance of Plutella xylostella (L.) (Lepidoptera: Plutellidae) on canola cultivars

The diamondback moth, Plutella xylostella (L.) (Lepidoptera: Plutellidae), is an important insect pest of canola, Brassica napus L., in Ardabil, Iran. Host plant resistance is an essential component of integrated management of P. xylostella. We investigated the preferences and performance of P. xylostella on nine commercial cultivars of canola, namely Zarfam, RGS003, Adder, Okapi, Opera, Hyola401, Ebonite Option500 and Elite under greenhouse conditions at 23 ± 1°C, 50 ± 5% RH and 14L:10D. In free-choice situation, oviposition was lowest on Opera (23.5) and highest on Zarfam (44.7). In the life table study, fecundity of new generation female moths was lowest on Opera (95.4) and highest on Adder (145.7). Survival from egg to adult was significantly lower on Opera, Option500 and Hyola401 than on other tested cultivars. The intrinsic rate of natural increase (r m) and population growth rate (λ) were lowest on Opera and highest on Zarfam. The generation time (T) was shortest on Zarfam (17.2 days) and longest on Hyola401 (19.9 days) whereas doubling time (DT) was longest on Opera (3.9 days) and shortest on Zarfam (3.0 days). Our results clearly suggest that Opera was the most resistant host among the tested cultivars and has the potential to be used in the integrated management of P. xylostella.

Life tables for sunn pest,Eurygaster integriceps(Heteroptera: Scutelleridae) in northern Iran

Life table studies of sunn pest were carried out in Varamin, Iran, from 1998-2001 in order to determine stage-specific mortalities and the impact of specific natural enemies on population dynamics. Populations were sampled 2-3 times weekly in agricultural fields during the growing season and monthly during the period of dormancy at resting sites in nearby mountains some 30 km away from cereal fields. Adults spend a period of 9-10 months in diapause and suffered overcompensatory, density-dependent mortality during this period. Variation in adult overwintering survival was inferred to be largely a function of the physiological condition of bugs that is reduced in a density-dependent manner by intraspecific competition for food among newly molted adults prior to migration to resting sites. Adult mortality emerged as the primary factor in key factor analysis, contributing 73% of the total variance in mortality. Other important factors were egg parasitism by Trissolcus vassilievi Mayr and adult parasitism by several species of Tachinidae. Although T. vassilievi made only a minor contribution to overall variance in total mortality, it had a significant effect on the number of newly molted adults, the life stage that is most damaging to cereal crops. The equilibrium level of the pest population in wheat fields was inferred to be ca. 72.6 adults m(-2), a number that substantially exceeds the economic threshold that ranges from 3-5 adults m(-2).

Mortality factors affecting the cabbage seedpod weevil, Ceutorhynchus obstrictus (Marsham), in its area of origin: A life table analysis

The cabbage seedpod weevil, Ceutorhynchus obstrictus (Marsham) (Coleoptera: Curculionidae), is a widely distributed invasive pest of cruciferous crops in North America. Control measures rely mostly on the application of insecticides but alternative control strategies such as classical biological control are under evaluation. To investigate the impact of parasitoids and other mortality factors on C. obstrictus populations, life table studies were conducted between 2005 and 2007 in 13 winter oilseed rape fields in Switzerland, part of the native range. Under field conditions females only realized approximately 50% of their potential lifetime fecundity, varying between 96 and 631 eggs per individual. Total generational mortality was higher than 99.6% in each year. Overwintering mortality of adults was the major population limiting factor, contributing approximately 50% to the overall generational mortality of C. obstrictus, whereas factors acting on the immature stages were responsible for the remaining 50%. Among the mortality factors of the immature stages, egg, larval and pupal mortality contributed 9–12%, 25–28% and 4–6% to the generational mortality, respectively. Larval ecto-parasitism on its own accounted for 7–15% of the generational mortality. Comparison of life table data presented here with that from North America will be invaluable for elucidating the mortality factors that regulate C. obstrictus populations in Europe, the region of origin.

Parasitism of a Hawaiian Endemic Moth by Invasive and Purposely Introduced Hymenoptera Species

The impact of invasive alien species on native organisms is a cause for serious concern. This concern is especially relevant in the Hawaiian archipelago because of its high level of endemicity, severe impacts of accidental introductions of invasive species, and long history of purposeful biological control introductions. Results from a previous study showed that the parasitoid assemblage associated with an endemic moth Udea stellata (Butler) comprised seven species: three adventive species, two purposely introduced species, and two of unknown origin. The objectives of this study were to assess the parasitism levels of alien wasps on populations of U. stellata at different sites and to determine the specific stages that were used by the spectrum of parasitoid species that attack U. stellata. Standardized collections of wild larvae were conducted at eight sites located on the islands of Kauai, Oahu, and Hawaii. In total, 3,531 larvae were collected in a 2-yr survey. Of these, 8.0% were collected as first instar, 23.0% as second instar, 39.0% as third instar, 21.0% as fourth instar, 7.1% as fifth instar, and 1.8% as sixth instar. Of the larvae that survived laboratory rearing, 43.0% were parasitized. Information collected in the surveys was complemented with data from life-table studies to determine stage-specific parasitism. All larval stages were susceptible to parasitism by at least one parasitoid species; second and third instars were susceptible to attack by all seven parasitoid species. Adventive parasitoids rather than purposely introduced ones were responsible for the greater part of the apparent mortality observed. At low and low-medium elevations, the parasitoid assemblage was dominated by adventive species. The two purposely introduced parasitoids were present in remote relatively undisturbed sites on the islands Kauai and Hawaii. The sometimes high parasitism rates by adventive species found in this study were shown to have minimal effect at the population level in our life table study; therefore, care should be taken when interpreting field parasitism data. Carefully addressing current ecological impacts of alien parasitoids on native species is of particular importance for developing more efficient means to quantify the risks of future biological control introductions.

Effects of cyanobacteria on fitness components of the herbivore Daphnia

Cyanobacteria are known to negatively affect their herbivores either by being of low nutritional value, by clogging the feeding apparatus or by producing toxins, and specifically, the role of toxins has been debated. Hence, in order to assess to what extent cyanobacterial toxins affect a major herbivore (Daphnia magna) that has had previous experience of cyanobacterial toxins, we conducted a life-table study using two otherwise-similar strains of Microcystis aeruginosa, one producing and one not producing the toxin microcystin. In contrast to previous studies, we found that Daphnia population growth was positive (r > 0.1 day(-1)) on a diet containing toxic Microcystis. However, we also found that the presence of the toxin negatively affected early survival and population growth of a microcystin-tolerant D. magna clone. Although there was no effect of toxin presence on per-capita fecundity of surviving adults, Daphnia produced smaller neonates when fed toxin-containing M. aeruginosa than when fed the non-toxic mutant. Hence, although Daphnia survival, population growth and neonate size were negatively affected by microcystin presence, Daphnia populations that have prior experience with toxic cyanobacteria may show positive population growth even at high concentrations of cyanobacterial toxins. This conclusion may have considerable implications for interactions between toxic cyanobacteria and herbivores in natural systems. (Less)

Resistance of some canola cultivars to Myzus persicae (Hemiptera: Aphididae)

The green peach aphid, Myzus persicae (Sulzer) (Hemiptera: Aphididae), is an important insect pest of a canola crop Brassica napus L., in Ardabil, Iran. Host plant resistance is an essential component of the integrated management of M. persicae. In field experiments, the population density of M. persicae was higher on Zarfam and lower on Ebonite, Elite, Okapi, RGS003, and Opera among the 19 canola cultivars during 2008 and 2009. In a free-choice situation, the numbers of attracted aphids per plant was lowest on Opera (1.2). In the life table study, aphids reared on Opera had the shortest adult longevity (8.3 days), lowest numbers of progeny per female (15.4) and the lowest survival rate (62.5%) compared to the other five cultivars. The intrinsic rate of the natural increase (rm) and population growth rate (λ) were lowest on Opera and highest on Zarfam. The generation time (T) was shortest on Opera (11.7 d) and longest on RGS003 (13.1 d), whereas the doubling time (DT) was longest on Opera (3.58 d) and shortest on Zarfam (2.26 d). Our results clearly suggest that Opera was the highest resistant host among the tested cultivars and has the potential to be used in the integrated management of M. persicae.

Using classification tree analysis to reveal causes of mortality in an insect population

Invasive species pose significant threats to native and managed ecosystems. How- ever, it may not always be possible to perform rigorous, long-term studies on invaders to determine the factors that influence their population dynamics, particu- larly when time and resources are limited. We applied a novel approach to determine factors associated with mortality in larvae of the sawfly Profenusa thomsoni Konow, a leafminer of birch, and a relatively recent invader of urban and rural birch forests in Alaska. Classification tree analysis was applied to reveal relationships between qualitative and quantitative predictor variables and categorical response variables in a large data set of larval mortality observations. 2 We determined the state (living or dead) of sawfly larvae in samples of individual leaves. Each leaf was scored for variables reflecting the intensity of intra-specific competition and leaf quality for leafminers, year of collection and degree-days accumulated were recorded for each sample. We explored the association of these variables with larval state using classification tree analysis. 3 Leafminer mortality was best explained by a combination of competition and resource exhaustion and our analysis revealed a possible advantage to group feeding in young larvae that may explain previously observed patterns of resource over- exploitation in this species. Dead larvae were disproportionately found in smaller leaves, which highlights the potential effect of competition on mortality and suggests that smaller-leaved species of birch will better able to resist leafminer damage. 4 We show that classification tree analysis may be useful in situations where urgency and/or limited resources prohibit traditional life-table studies.

Epigenetic gambling and epigenetic drift as an antagonistic pleiotropic mechanism of aging

Generations of biogerontologists have been puzzled by the marked intraspecific variations in lifespan of their experimental model organisms despite all efforts to control both genotype and environment. The most cogent example comes from life table studies of wild-type Caenorhabditis elegans when grown in suspension cultures using axenic media. While nuclear and mitochondrial somatic mutations and 'thermodynamic noise' likely contribute to such lifespan variegations, I raise an additional hypothetical mechanism, one that may have evolved as a mechanism of phenotypic variation which could have preceded the evolution of meiotic recombination. I suggest that random changes in cellular gene expression (cellular epigenetic gambling or bet hedging) evolved as an adaptive mechanism to ensure survival of members of a group in the face of unpredictable environmental challenges. Once activated, it could lead to progressive epigenetic variegation (epigenetic drift) amongst all members of the group. Thus, while particular patterns of gene expression would be adaptive for a subset of reproductive individuals within a population early in life, once initiated, I predict that continued epigenetic drift will result in variable onsets and patterns of pathophysiology--perhaps yet another example of antagonistic pleiotropic gene action in the genesis of senescent phenotypes. The weakness of this hypothesis is that we do not currently have a plausible molecular mechanism for the putative genetic 'randomizer' of epigenetic expression, particularly one whose 'setting' may be responsive to the ecology in which a given species evolves. I offer experimental approaches, however, to search for the elusive epigenetic gambler(s).

Life Table and Population Parameter of Sogatella furcifera (Horvath) (Homoptera: Delphacidae) on Rice

Survivorship and fertility of the White Backed Plant Hopper (WBPH), Sogatella furcifera were assessed under laboratory conditions in Myanmar. A pair of five days old WBPH was released into a wooden cage covered with wire mesh sieve. Thirty days old rice plant in a pot was placed on the floor of the wooden cage. The single sex method was applied in the life table study. Life tables and population parameters were constructed based on unlimited food supply and a natural enemies-free environment. Results showed that the highest mortality occurred in the immature stages, especially in the first and second instars. The life table analysis showed that population densities of S. furcifera decreased gradually. The proportion of male to female observed was 1:0.88. The females could live for a maximum of 12 days. The trend of oviposition showed a peak at about the 10th day of the female life span. The mean number of eggs produced per female was 8.75. The intrinsic rate of increase (rm) was 0.06999 per female per day and daily finite of increase (λ) was 1.0255 per female per day, with a mean generation time (T) of 34.97 days. The net reproductive rate (Ro) of the population was 9.2732. The population Doubling Time (DT) was within 10.88 days. It could be concluded that the survivorship curve reflected a modest rate of mortality during the early life stages and a gradual reduction when approaching adulthood. All the surviving nymphs underwent four moults. The life table showed that about 37.26% of S. furcifera eggs successfully emerged as adults and high mortality occurred during the early immature stages. This type of survivorship is commonly classified as type II.