Nymph Production Research Articles

Alfalfa (Medicago sativaL.) shoot saponins: identification and bio-activity by the assessment of aphid feeding

Biochemical components in alfalfa (Medicago sativa L.), such as saponins, can act as protecting factors against bio-stresses. Saponins are also antifeedants and show oral toxicity towards higher and lower animals. Changes in saponins, such as variation in the carbon skeleton, or hydrolysis of saponin glycosides and other conjugates, may change their biological effects. The aims of this research were to study saponin variation in different growth stages of alfalfa and to investigate the biological role of saponins in the spotted alfalfa aphid, Therioaphis maculata. Saponins from alfalfa shoots in different growth stages were extracted, chemically purified and analysed by TLC. Specific saponins such as soyasaponin1 from root and shoot and two bisdesmosides of medicagenic acid, one from shoot and another from root tissues, were identified using reference compounds allowing changes in saponin composition during plant development in different shoot tissues of alfalfa to be assessed. The response of the alfalfa aphid to feeding on alfalfa in different growth stages was studied. No significant difference in the survival of aphids, from neonate to adult, was observed, but due to the antibiotic effects of saponins, two differences were found in the onset of nymph production and cumulative nymph production. The results show that the saponin composition in alfalfa changes with plant development and this, in turn, can often negatively affect the development of specific insect pests such as the spotted alfalfa aphid, suggesting a possible biological role of alfalfa saponins.

Biological responses of the Sipha flava (Forbes, 1884) (Hemiptera: Aphididae) fed with different elephant grass genotypes

This work aimed to evaluate the effect of genotypes of elephant grass, Pennisetum purpureum Schum, on some biological aspects of Sipha flava (Forbes). Foliar disks of 15 elephant grass genotypes were used, on which individual nymphs up to 12 hours old were placed in dishes and kept at 25 oC, RH of 70 ± 10% and 12-hour photophase. We evaluated the number of instars, duration and survival of each instar and the entire nymphal period, duration of the pre-reproductive, reproductive and post-reproductive period, daily and total nymph production capacity and longevity of the adults and biological cycle (nymph-adult). The nymphs passed through four instars on all the elephant grass genotypes studied. There were no significant differences in the duration of the first and last nymph stages on the different genotypes, unlike observed for the intermediate instars and nymphal period . The biological parameters of the adult phase of the aphid, such as pre-reproductive, reproductive and post-reproductive period and longevity, were also affected by the genotype. Cameroon de Piracicaba and Guacu IZ2 were the most suitable genotypes for development of the aphids, providing higher values for overall production of nymphs/female, daily production of nymphs/female, reproductive period and adult longevity. On the other hand, the Sem Pelo genotype was the least suitable for the aphids’ development and reproduction according to the biological parameters studied.

The Impact of Temperature on Biological Aspects and Life Table ofRhopalosiphum padi(Hemiptera: Aphididae) Fed with Signal Grass

ABSTRACT The impact of temperature was evaluated on Rhopalosiphum padi (L.) (Hemiptera: Aphididae). Nymphs, 12-h-old, were placed individually in cylindrical plastic dishes (2.5 × 2.5 cm), with a layer of 1% agar in which leaf disks of signal grass had been placed. The nymphs were reared at 12, 16, 20, 24, 28, and 32°C ± 1°C, RH of 70 ± 10% and 12-h photophase. We evaluated number of instars, duration of each instar and the nymphal period, survival of instars, duration of the reproductive period, daily and total production of nymphs, and longevity of the nymphal and adult phases. To construct the life expectancy table and fecundity, daily observations were made of 70 nymphs at each temperature, from birth to death. Development of R. padi was faster with increased temperature, but they did not complete the last nymphal instar at 32°C. The same pattern occurred for the pre-reproductive, reproductive, and post-reproductive periods. The highest fecundity rates were between 16°C and 24°C. The highest fertility...

Resistance of squash cultivars to Aphis gossypii

The Cucurbitaceae plants are damaged by attack of a wide spectrum of insects and microorganisms. Among the sucker insects causing damages on squash Cucurbita pepo (L.), the aphid Aphis gossypii (Glover) (Hemiptera: Aphididae) is pointed as one of the most important, once their nymphs and adults suck the sap of the leaves continuously, besides being potential vector of virus. The present research evaluated different cultivars, aiming to identify the resistance against this aphid. The cultivars Novita, Sandy, Caserta Cac Melhorada, Novita Plus, Samira, AF-2858 and Caserta TS were used in laboratory assays (T= 25±2ºC; RH= 70±10% and fotophase= 12 h). In the immature phase the duration of nymphal instars was evaluated, the total duration and their viability, confining individuals on leaf disks from cultivars. In the adult phase the duration of reproductive period, the fecundity and the biological cycle were observed. The cultivar 'Sandy' expressed high level of antibiosis and feeding non-preference against A. gossypii, increasing the nymphal stage and causing mortality near to 70%. Besides, this cultivar reduced the production of nymphs and the longevity of the insects. The 'Novita Plus' cultivar also induced significant nymphal mortality, however in lower levels than those verified in 'Sandy', indicating a moderate resistance.

The ecological differentiation of asexual lineages of cotton aphids: alate behaviour, sensory physiology, and differential host associations

The cotton aphid (Aphis gossypii Glover) is a cosmopolitan pest species consisting of various host plant-associated lineages that appear to have different patterns of insecticide resistance, electrophoretic banding, and reproductive output across alternative host species. Debate continues as to whether these differences represent intraspecific variation or indicate a complex of cryptic or sibling species. We studied the host plant-related ecology of two asexual lineages of A. gossypii associated with the families Malvaceae and Cucurbitaceae, respectively, in particular the host plant finding and acceptance processes of the alate forms. The two lineages proved to be differentiated across host plants in terms of: (1) their landing and settling behaviour, nymphal production rate, and subsequent colony establishment (i.e. nymphal survival and development) and (2) their sensory abilities in relation to host plant-derived odours. Furthermore, genetic structuring according to host plant type was detected using the gene for elongation factor 1-α. The magnitude of the genetic differentiation across lineages was low, perhaps indicating a relatively recent divergence. The results demonstrate: (1) the presence of (at least) two cryptic species within the current definition of A. gossypii, as anticipated in previous studies, and (2) the practicalities of using a multidisciplinary approach to understanding the 'limits' of asexual species. If sexuals can be generated from each of these lineages, this conclusion will be open to further testing.

The influence of some cabbage cultivars on green peach aphid Myzus persicae Sulz. and the distribution of the parasitoid Diaeretiella rapae (Mcintosh) (Hymenoptera: Aphidiidae)

Laboratory and field studies were undertaken to evaluate the influence of four cabbage cultivars, Kandura, Royal, Dabana and Red, on some biological aspects of green peach aphid Myzus persicae Sulz. (Homoptera: Aphididae) and on the distribution of the parasitoid Diaeretiella rapae Mcintosh. (Hymenoptera: Aphidiidae). Results indicated that production of young nymphs per female varied depending on the cultivar. The highest progeny production was 23.7 nymph/ female recorded on the cultivar Kandura and the lowest number was 7.3 nymphs/ female on Red cabbage. Females produced an average of 4.8 and 1.3 nymph when fed on the two cultivars respectively. The parasitoid D. rapae was found associated with the aphid and varied according to the host cabbage cultivar. The highest percentages of parasitism was 28% on Kandura cultivar and the lowest was 7% recoded on aphid fed on Red cabbage. Field studies showed that there were 8 generations for green peach aphid during the course of this study which lasted from the beginning of December to the end of March. the length of generation decreased with the increasing of temperature and varied according to cabbage cultivar. The activity of the parasitoid also varied with cultivar and temperature. The highest percentage of parasitism was 28% recorded on Kandura in the beginning of January. The red cabbage was the least preferred host plant for the D. rapae being the highest percentage of parasitism 7% observed late in February .Results also indicated that the parasitism increased with the increasing density of aphid. Therefore any control practice should take in consideration all possible means that would lead to conserve and assist this parasitoid in the field.

Desenvolvimento e reprodução de Sipha flava (Forbes) (Hemiptera: Aphididae) em diferentes temperaturas

The aphid Sipha flava (Forbes) is a pest on elephant grass, but little is known about its biology. The objective of this work was to evaluate the temperature effects on the development, survival and reproduction of S. flava fed on Pennisetum purpureum. Twelve-hour-old nymphs were individualized on sections of elephant grass blades and maintained at 12, 16, 20, 24, 28 and 32 degrees C+/-1 degrees C, UR 70+/-10% and 12 h photophase. A total of 150 nymphs were used per treatment divided in 30 replicates, using a totally random design. The lower threshold temperatures (LTT) for first, second, third and fourth instars were 0.83, 1.05, 3.01 and 4.98 degrees C, respectively, indicating a change in thermal requirements as the development progress. The LTT for the whole nymphal stage was 2.08 degrees C, pointing to the tolerance of this species to low temperatures. A significant reduction in survival was observed at high temperatures (28 and 32 degrees C). Although the reproductive periods were longer and insects lived longer at 12 degrees C as compared with those at higher temperatures, the total fecundity was substantially reduced. The overall life cycle duration was almost twice as long at 12 degrees C than at 24 degrees C. The greatest daily production of nymphs and greatest number of nymphs produced overall occurred at 24 degrees C. The temperatures of 20 degrees C and 24 degrees C were more suitable to S. flava development and reproduction.

Life tables and demographic statistics of Russian wheat aphid (Hemiptera: Aphididae) reared at different temperatures and on different host plant growth stages

Laboratory experiments were used to investigate the influences of 25 combinations of temperature and barley plant growth stage (5 × 5 factorial combination of temperature and barley plant growth stage) on the development, survival and reproduction of the Russian wheat aphid (RWA), Diuraphis noxia (Mordvilko). For each of the 25 treatments, the developmental time and nymphal production of 72 RWA individuals were recorded (1800 RWA in total) throughout their entire lifetimes. The collected data were used for analyzing demography, modelling phenology, and simulating population growth of RWA. In this paper, the results of demographic analyses are reported. Specifically, for each treatment, cohort life tables, reproductive heterogeneity tables (parity and birth intervals), and reproductive schedule tables were constructed, and demographic parameters such as intrinsic rate of increase, life-span, fecundity, life table entropy, etc. calculated. Based on these analyses, the most important summary demographic statistics are reported. Using the intrinsic rate of increase (rm) as an example, a procedure is demonstrated that builds a dynamic rm model by applying the Best Subset Regression approach. A more comprehensive (considering reproductive heterogeneity and schedule tables) yet concise (comprising dynamic rm models) demographic model than that based on standard life table analysis alone is presented.

Ciclo de vida de Triatoma dimidiata Latreille, 1811 (Hemiptera, Reduviidae) en condiciones de laboratorio: producción de ninfas para ensayos biológicos

Despite the importance of Triatoma dimidiata as a vector of Chagas disease, little is known of its life cycle and the efficient production of these insects for biological tests. Life cycle characteristics in the laboratory were described and optimum nutritional conditions were established for the efficient production of nymphs V stage for biological tests. We determined the time of development of the nymphal stage under controlled laboratory conditions until reaching the adult stage. In a massive rearing of stage V nymphs, fed and weighted after varying periods of fasting, distributed in weight ranges to obtain the largest proportion of individuals. The time mean from egg to adult was 269 days, with a wide range of duration (174 to 598 days) and the times required for 1st, 2nd, 3rd, 4th and 5th stage development was 33, 37, 41, 61 and 69 days, respectively, with a mortality of 22%. The optimum treatment was 22 days of fasting, in which 76% of the nymphs reached stage V with a weight range from 201 to 300 mg. Triatoma dimidiata presented development time with broad range for some individuals, possibly due to the irregularity in the food availability. A homogenous weight range was attained with a regime of 22 days of fasting with an optimum production of stage V nymphs.

A new modelling approach to insect reproduction with same-shape reproduction distribution and rate summation: with particular reference to Russian wheat aphid

Same-shape distribution model and rate summation approach are widely used to describe the insect developmental process. In this approach, by integrating a nonlinear deterministic developmental rate model and a probabilistic same-shape distribution model, the proportion of the cohort completing development is quantified as a function of accumulating developmental rates, which themselves are temperature dependent. This method is considered to be more accurate in modelling insect phenology because it can address a well-known biological fact, individual variability, that insect individual developmental rates respond to temperature differently, and because rate-summation essentially simulates developmental rates under variable temperatures instead of constant temperatures. By comparing insect development and reproduction with respect to their responses to temperatures, we argue for the extension of the same-shape and rate-summation approaches to modelling insect reproduction process under variable temperatures. We justify our arguments by the fact that individual variation universally exists in almost all biological characteristics, and the phenomenon that insect development and reproduction respond to temperature very similarly, which is supported by some endocrinological evidences reported in literature. In addition, the approach for testing the applicability of the original same-shape developmental modelling, experimentally verifying the sameness of the same-shape curves or that the shape of the curves is invariant with respect to the temperature regimes, equally applies to our extended version for reproduction modelling. We successfully tested the extension and its applicability with our experimental data of 1800 Russian wheat aphids' (RWA) (Diuraphis noxia (Mordvilko)) reproduction under various temperature and plant growth stage regimes. We also extended Taylor's (1981) nonlinear model for insect development to describe RWA mean (median) nymphal production under different temperatures and barley plant growth stages. Three same-shape distribution models, Weibull distribution, Stinner's model and logistic model, are used to construct the same-shape reproduction distribution models for RWA. The extensions performed in this paper contribute a new modelling approach for predicting insect reproduction under field variable temperatures and plant growth stages. The prediction model can be parameterized with data from typical laboratory demography experiments and further integrated into simulation models for insect population dynamics. Finally, we discussed why the sameness test of the same-shape distribution curves is sufficient in validating the approach and proposed a strategy for dealing with exceptional cases where the sameness test fails.

Phenology and Development of the Yellow Rose Aphid, Acythrosiphon porosum (Sanderson), in Northern Florida and Southern Georgia

The yellow rose aphid, Acythrosiphon porosum (Sanderson), is a cosmopolitan pest of roses and strawberries. Acythrosiphon porosum is one of only a few arthropod pests of roses occurring in northern Florida and southern Georgia. Hybrid roses are widely planted around the city of Thomasville, GA, which is known as the Rose City. Three ‘Grandiflora’ rose cultivars ‘Queen Elizabeth’, ‘Roundelay’ and ‘Spartan’ were used to determine cultivar and location effects on A. porosum seasonal abundance and natural enemies. Developmental rate, longevity and nymph production of A. porosum were also investigated at 4 temperatures, 10.0, 15.5, 21.1, and 26.7°C, in environmental chambers using cut leaf discs of ‘Queen Elizabeth’ on agar plates. Acythrosiphon porosum occurred throughout much of the year except for the coldest winter and warmest summer months and reached highest populations during the cooler weather of spring and fall. Cultivar differences were statistically significant at all locations where ‘Queen Elizabeth’ averaged higher aphids per leaf than ‘Roundelay’, which averaged higher aphids than ‘Spartan’. Aphid numbers did not significantly differ in comparisons of leaves sampled from the bottom, middle or top third of the plant's canopy height. Developmental rate calculated as the time from nymph to nymph was most rapid (x̄ = 10.3 d) at 21.1 °C, but no aphid development was observed at 26.7°C. Total egg production was highest (x̄ = 27.5 nymphs per aphid) at 10.0°C as was longevity of 60.1 d. Highest nymph production (1.5 per d) was observed at 21.1 °C. Many generalist predators and two parasitoid species were found in low numbers attacking A. porosum: Syrphophagous aphidovorus (Mayr) (Hymenoptera: Encyrticidae) and Ephedius sp. (Hymenoptera: Aphidiidae).

Temperatura no desenvolvimento e na reprodução de cochonilhas criadas sobre abóboras

O desenvolvimento de insetos é dependente da temperatura. Nesta pesquisa, foi verificada a influência da temperatura no desenvolvimento e na reprodução de Chrysomphalus aonidum (L.) em câmaras climatizadas com UR do ar 70±10%, fotofase de 12h e temperaturas constantes de 17, 19, 21, 23, 25 e 27 ± 1°C, tendo como substrato abóboras "cabotiá" (Curcubita maxima x Curcubita moschata var. Tetsukabuto). Foi observada a influência da temperatura nos parâmetros biológicos da cochonilha, sendo que temperaturas entre 23 e 27°C foram as mais adequadas ao inseto, propiciando menor duração do período ninfal e maior produção diária de ninfas por fêmea. Temperaturas entre 17 e 19°C provocam maior duração na fase ninfal, maior longevidade das fêmeas e menor produção diária de ninfas por fêmea.

Development of methods to evaluate susceptibility of soybean aphid to imidacloprid and thiamethoxam at lethal and sublethal concentrations

AbstractThe soybean aphid, Aphis glycines Matsumura (Homoptera: Aphididae), is a recent introduction (2000) from Asia and has become a serious soybean [Glycine max (L.) Merr. (Fabaceae)] pest in North America. Seed treatments using the neonicotinoid insecticides, imidacloprid and thiamethoxam, have been suggested as a method of control, and the use of these insecticides is becoming widespread. As a consequence, there is increased potential to select for resistance to these compounds. In the case of soybean aphids, baseline susceptibility to neonicotinoid insecticides and standardized methods for bioassay are lacking. A bioassay technique that uses excised soybean leaves immersed in an insecticide solution was developed to determine systemic insecticidal activity at lethal and sublethal concentrations. Mortality and population growth inhibition were evaluated after 7 days. Life table parameters were calculated by exposing 1‐day‐old aphids to three concentrations of thiamethoxam. Aphid mortality and nymph production were recorded daily until the entire cohort collapsed. Soybean aphid age‐specific survivorship, fecundity, net reproductive rate, longevity, intrinsic rate of increase, discrete daily growth rate, and life expectancy were all significantly reduced at higher thiamethoxam concentrations. Soybean aphid response to both insecticides was similar, and both compounds were very toxic with LC50s of 31.3 and 16.9 ng ml−1 and EC50s of 6.3 and 5.4 ng ml−1 for imidacloprid and thiamethoxam, respectively. These results indicate that the methods developed in this study had negligible impact on the life table estimates measured and can be used to develop a baseline of susceptibility as a benchmark for subsequent resistance monitoring. Given the rapid and widespread adoption of this new insecticide class, vigilant monitoring for changes in susceptibility will be essential to its long‐term sustainability.

促成栽培ピーマンに処理された粒剤のモモアカアブラムシに対する残効期間

We examined the residual effects of the granular insecticides applied on sweet pepper plants on the survival of the green peach aphid, Myzus persicae. Sweet pepper seedlings were transplanted in a green house after applying imidacloprid or nitenpyram granules at the recommended dosage of 2 g ⁄ plant. Then, an upper leaf and a lower leaf were taken from each plant at 5, 12, 19 and 26 days after the insecticide treatment and were examined. Each test leaf was set in a Munger cell into which 10 adult female green peach aphids were released. The survival of the aphids and the number of nymphs laid by these insects were determined after 48 hours. The leaves from the plants treated with imidacloprid exhibited high insecticidal activity and suppressed the production of nymphs at 5 and 12 days after the insecticide treatment. The lower leaves retained a high residual effect for 19 days, but the residual effect in the upper leaf was considerably reduced after the same period. The effect of imidacloprid application disappeared at 26 days. The leaves treated with nitenpyram exhibited high insecticidal effect and suppressed the production of nymphs at 5 and 12 days, although the mortality rate of aphids on the upper leaves started to decrease on the 12th day after the insecticide treatment. The effect of nitenpyram application almost disappeared with some residual effect on nymph production on the 19th day. Therefore, it is necessary to initiate other control methods for transplanted seedlings when the effectiveness of the initial treatment is diminished.

Optimal Reproduction Strategies in Two Species of Mound-Building Termites

We formulate a mathematical model for food collection and production of workers and nymphs in 2 species of mound building termites. We maximise the number of nymphs (reproductives) produced by each colony over its lifetime with respect to the proportion of eggs that hatch as nymphs as opposed to workers. The results predict that food storage has a very important influence on the pattern of nymph and worker production. Food storage affects the part of the year that nymph production dominates, whether nymphs and workers are produced at the same time or not, and the existence of a final phase in the colony's life when a very large number of nymphs but no workers are produced.

Beet Leafhopper (Hemiptera: Cicadellidae) Settling Behavior, Survival, and Reproduction on Selected Host Plants

Experiments were conducted to determine the settling behavior, survival, and reproduction of the beet leafhopper, Circulifer tenellus (Baker), when maintained on selected host plants. This leafhopper was recently identified in the Columbia Basin of Washington and Oregon as the probable vector of the beet leafhopper-transmitted virescence agent phytoplasma, causal agent of several vegetable crop diseases, including potato purple top. Plants selected for study were sugar beet, Beta vulgaris L.; radish, Raphanus sativus L.; dry bean, Phaseolus vulgaris L.; potato, Solanum tuberosum L.; carrot, Daucus carota L.; and tomato, Lycopersicon esculentum Mill. Leafhopper adults were confined on caged plants, and settling behavior was observed during a 72-h period and survival was monitored for 40 d. Also, oviposition and nymphal production were investigated by maintaining leafhoppers for approximately 90 d on each of the selected plants. Sixty to 100% of leafhoppers settled on all studied plants during the first 5 h, but settling on bean and tomato declined sharply thereafter. Leafhopper mortality was very high on bean and tomato, with 95 and 65% of the leafhoppers, respectively, dying in about a week. In contrast, 77, 90, and 95% of leafhoppers maintained on potato, sugar beet, and radish, respectively, survived until the end of the 40-d experimental period. Beet leafhopper oviposition and nymphal production and development only occurred on sugar beet, radish, and potato; reproduction was lower on potato.

Beet Leafhopper (Hemiptera: Cicadellidae) Settling Behavior, Survival, and Reproduction on Selected Host Plants

Experiments were conducted to determine the settling behavior, survival, and reproduction of the beet leafhopper, Circulifer tenellus (Baker), when maintained on selected host plants. This leafhopper was recently identified in the Columbia Basin of Washington and Oregon as the probable vector of the beet leafhopper-transmitted virescence agent phytoplasma, causal agent of several vegetable crop diseases, including potato purple top. Plants selected for study were sugar beet, Beta vulgaris L.; radish, Raphanus sativus L.; dry bean, Phaseolus vulgaris L.; potato, Solanum tuberosum L.; carrot, Daucus carota L.; and tomato, Lycopersicon esculentum Mill. Leafhopper adults were confined on caged plants, and settling behavior was observed during a 72-h period and survival was monitored for 40 d. Also, oviposition and nymphal production were investigated by maintaining leafhoppers for ≈90 d on each of the selected plants. Sixty to 100% of leafhoppers settled on all studied plants during the first 5 h, but settling on bean and tomato declined sharply thereafter. Leafhopper mortality was very high on bean and tomato, with 95 and 65% of the leafhoppers, respectively, dying in about a week. In contrast, 77, 90, and 95% of leafhoppers maintained on potato, sugar beet, and radish, respectively, survived until the end of the 40-d experimental period. Beet leafhopper oviposition and nymphal production and development only occurred on sugar beet, radish, and potato; reproduction was lower on potato.

Enhancement of resistance to aphids by introducing the snowdrop lectin genegna into maize plants

In order to enhance the resistance to pests, transgenic maize (Zea mays L.) plants from elite inbred lines containing the gene encoding snowdrop lectin (Galanthus nivalis L. agglutinin; GNA) under control of a phloem-specific promoter were generated through the Agrobacterium tumefaciens-mediated method. The toxicity of GNA-expressing plants to aphids has also been studied. The independently derived plants were subjected to molecular analyses. Polymerase chain reaction (PCR) and Southern blot analyses confirmed that the gna gene was integrated into maize genome and inherited to the following generations. The typical Mendelian patterns of inheritance occurred in most cases. The level of GNA expression at 0.13%-0.28% of total soluble protein was observed in different transgenic plants. The progeny of nine GNA-expressing independent transformants that were derived separately from the elite inbred lines DH4866, DH9942, and 8902, were selected for examination of resistance to aphids. These plants synthesized GNA at levels above 0.22% total soluble protein, and enhanced resistance to aphids was demonstrated by exposing the plants to corn leaf aphid (Rhopalosiphum maidis Fitch) under greenhouse conditions. The nymph production was significantly reduced by 46.9% on GNA-expressing plants. Field evaluation of the transgenic plants supported the results from the inoculation trial. After a series of artificial self-crosses, some homozygous transgenic maize lines expressing GNA were obtained. In the present study, we have obtained new insect-resistant maize material for further breeding work.

Virulence, horizontal transmission, and sublethal reproductive effects of Metarhizium anisopliae (Anamorphic fungi) on the German cockroach (Blattodea: Blattellidae)

Virulence of Metarhizium anisopliae (Metschnikoff) Sorokin strain EAMa 01/121-Su against the German Cockroach, Blatella germanica (L.), was determined using four concentrations ranging from 4.2 × 10 6 to 4.2 × 10 9 spores per milliliter. The LD 50 value was 1.4 × 10 7 spores per milliliter (56,000 spores per cockroach) and LT 50 values were 14.8 days and 5.3 days for 4.2 × 10 8 and 4.2 × 10 9 spores per milliliter, respectively. An experiment was conducted to evaluate whether a fungal transmission could exist among infected and healthy cockroaches. Percentage mortality at a ratio of 1:10 of infected to unexposed cockroaches was 87.5% and LT 50 was 12.2 days, which indicated the potential of this strain to be horizontally transmitted and to rapidly spread the infection in the insect population. The effect of a sublethal dose (ca. LD 60) of M. anisopliae EAMa 01/121-Su strain, applied topically on German cockroaches, was studied by reciprocal crossing. Othecal production, oothecal hatchability, and nymphal production declined upon exposure to M. anisopliae EAMa 01/121-Su strain. The mean number of oothecae laid by female was progressively and significantly reduced by fungal treatment from second oviposition period onwards. Oothecal hatch of fungally challenged females was reduced by 46–49%, oothecal viability by 48–85%, and nymphal production by 22–35%. Only treated females showed an effect on oothecal production, oothecal hatch, and nymphal production, although oothecal hatch was also governed by treated males at a higher significance level. Our results on virulence and horizontal transmission of fungal conidia of M. anisopliae EAMa 01/121-Su strain and its sublethal reproductive effects on German cockroach females are discussed in terms of its potential to decrease the pest status of B. germanica in the short and long terms.

Nymphs of the Formosan Subterranean Termite (Isoptera: Rhinotermitidae): Aspects of Formation and Transformation

Mature colonies of the Formosan subterranean termite, Coptotermes formosanus Shiraki, like most other termite species, produce a reproductive caste in the form of nymphs that subsequently give rise to alates. Temporal production of nymphs in C. formosanus was monitored in monthly collections from four field traps in New Orleans, LA. Nymphs were present throughout the year with peak numbers observed during October/November and May. Large nymphs first occurred in December and peaked in March. Fewer than 1.5% workers formed nymphs within 3 months after collection from the field and after removal of the preexisting nymphs. Collections from other colonies, kept in the laboratory for >2 yr, did not produce any nymphs. It is speculated that a nymph induction factor (NIF), possibly coming from a mature physogastric queen, elicits nymph formation. The same or a similar factor may also be responsible for further development of nymphs and their transformation to alates. In the absence of this latter factor, the nymphs, except those in the most advanced stage of development, are either cannibalized or transform into brachypteroid neotenics. A scheme for the formation and transformation of various developmental stages within each caste of C. formosanus is presented.