Preference For Eggs Research Articles

An Evaluation of Spodoptera littoralis and Spodoptera exigua as Natural Prey for the Generalist Predator Chrysoperla carnea

Chrysoperla carnea (Stephens) is a common generalist predator in agroecosystems, frequently used for the control of soft-bodied pests in augmentative releases. Better knowledge of its interactions with secondary natural prey is necessary to optimize field biocontrol performance. This work evaluates the eggs and early larvae of Spodoptera exigua (Hübner) and Spodoptera littoralis (Boisduval) as natural prey for the third larval instar of C. carnea, and the predator preferences for different prey stages under varying conditions, assessing the impact on its life cycle and reproduction, in comparison with commercial diets based on Ephestia kuehniella Zeller eggs. Prey choice results were uniform for each dual prey combination irrespective of previous predator conditions (larvae number or fasting). Chrysoperla carnea did not show preference for Ephestia or Spodoptera eggs, but preferred eggs prior to larvae of the natural prey. Diets based on the frozen eggs of natural and factitious prey species showed similar effects on the development and reproduction of predator, but when C. carnea fed on S. exigua larvae, several negative effects were assessed, such as longer preimaginal development, lower adult emergence, and a reduced fecundity. These results are helpful for improving the use of lacewings as biocontrol agents in pest control programs.

Research on Chinese consumers' shell egg consumption preferences and the egg quality of functional eggs

The purpose of this study is to investigate the characteristics of egg consumption in China and the production of functional eggs, and finally enrich the types of shell egg products. Trial 1 explored the influence of egg quality on Chinese consumers' willingness to purchase eggs through a questionnaire, which investigated 1,317 consumers' preferences for egg appearance, factors influencing egg purchase, and purchase of functional eggs. The results showed that about 65% of respondents ate more than 4 eggs per wk, pink eggs were the most popular in China, about 65% of consumers preferred eggs with an egg weight of 48 to 58 grams. For functional eggs, 75.32% of consumers have never heard of them. Preferences for eggshell color and yolk color varied by geographic region, with darker colors preferred in Northeast China. Based on the survey results of functional eggs consumption in Trial 1, the dwarf layers of China Agricultural University were used in Trial 2 to produce functional eggs. The eggs are small and pink in color, which is in line with the preferences of Chinese consumers. Three hundred dwarf layers were divided into 4 groups, using the linseed oil added, marigold extract added, and yeast selenium added diets to produce normal, n-3 fatty acid-enriched, lutein-enriched and selenium-enriched eggs by feeding for 28 d, determined the eggs' nutrient content and egg quality. The results showed that the n-3 fatty acid, lutein and selenium contents of the eggs of dwarf layers were significantly increased by changing the diets and did not affect the egg weight, eggshell strength, Haugh units or the proportion of egg parts. The results of this study are helpful to understand the trend of egg consumption preferences in China, and on this basis to produce functional eggs that meet the consumers' expectations.

No adverse effects of symbiotic control on the parasitism of Halyomorpha halys by egg parasitoids

The brown marmorated stink bug Halyomorpha halys is a polyphagous insect, which has a devastating impact on agricultural production in many countries. The alteration of symbiont vertical transmission, by removing symbionts from stink bug eggs (symbiotic control), has been recently introduced in control programmes against this insect. A major advantage of this strategy is the compatibility with natural enemies, since it allows an insecticide-free approach that is not harmful to other agroecosystem components. However, the effect of anti-symbiont products on parasitism by egg parasitoids is still unexplored. Here, we investigated the impact on parasitism by native (Anastatus bifasciatus, Ooencyrtus telenomicida and Trissolcus kozlovi) and exotic (Trissolcus japonicus and Trissolcus mitsukurii) parasitoids that attack H. halys eggs, after treatment with the micronutrient biocomplex Dentamet®, used for symbiotic control. The native wasp species were tested in no-choice bioassays, showing that treatment of the egg masses did not affect emergence percentages, but the non-reproductive effects were often reduced by the biocomplex. The exotic species T. japonicus and T. mitsukurii were used in no-choice and paired choice bioassays, showing an opposite influence of Dentamet® on emergence percentage and preference in the two species. No-choice tests indicated the highest successful parasitoid emergence on biocomplex-treated egg masses for T. japonicus, while no preference in the paired comparison with eggs treated with water or untreated. In contrast, T. mitsukurii displayed the lowest parasitism after Dentamet® treatment in no-choice tests, and preferred egg masses without Dentamet® in paired choice tests. We did not record any natural symbiont acquisition by the parasitoids emerged from H. halys egg masses, indicating that the wasp fitness is very unlikely to be altered by dysbiotic effects resulting from treatments. Therefore, our results support a further implementation of symbiotic control in different crops in combination with biological control, as sustainable options for H. halys integrated pest management.

Selection of suitable predatory mites against, Panonychus citri (McGregor) (Acari: Tetranychidae) using relative control potential metrics and functional response

BackgroundSelection of suitable predators for the control of the spider mite, Panonychus citri is always a challenge due to the lack of their reliable predicted efficacy. In this laboratory study, biological control potential of Neoseiulus californicus, N. cucumeris and Scapulaseius newsami, against P. citri using the “Relative Control Potential” (RCP) metric to compare their efficacies was evaluated. The functional response type was determined at different prey densities (after 24 h).ResultsThe type II functional responses were observed from all the tested predators feeding on 3 different life stages of P. citri, except N. cucumeris, which was fed only on eggs. All predatory mites preferred eggs of P. citri with a higher attack rate (1.397) in N. cucumeris, followed by N. californicus (1.238) and S. newsami (0.975). Handling time was also lower in N. cucumeris than other mites, with a trend as: for N. cucumeris, eggs > adults > immature stages; for N. californicus, immature stages > eggs > adults, while for S. newsami, eggs > immature stages > adults. The integration of greenhouse abundance and fecundity (%) data resulted in a higher RCP for N. cucumeris than other predators.ConclusionNeoseiulus cucumeris was selected as the most suitable predatory mite for the control of P. citri with a higher RCP and potential to maximum reproduction. S. newsami, which was used for the first time, gave almost similar results compared to N. californicus but with lower efficacy.

English

A study was conducted in different agro-ecologies of Ethiopia with the objective of understanding the farmers’ preferences towards breeding objectives in indigenous chickens. For the interview, 245 households (60 from lowland, 100 from midland and 85 from highland) were randomly selected. Farmers in lowland had significantly (p<0.05) lower chicken populations while comparing with the remaining agro-ecologies. The average age of village pullets at first egg was 6.54±0.063 months. There was significantly (p<0.05) higher egg production in midland. There was significant difference (p<0.05) in clutch number among the three agro-ecologies. Among the three agro-ecologies; midland showed significantly (p<0.05) higher number of eggs set/hen. Effective population size of village chickens per household was calculated as 4.43, 7.8 and 7.18 in lowland, midland and highland respectively. Most of the farmers (91%) were practicing culling their chickens for getting old, sickness, brooding frequency and low production for hens and getting old, sickness and fighting each other for cocks. Comparing the preferences of traits, female farmers preferred egg production, unlike the male farmers who gave equal emphasis both for egg and meat. Egg production for sale was prioritized by the farmers, especially for women, followed by live chicken sale. Body weight is the most considered trait to select male chickens for breeding, followed by plumage color, across thee agro-ecologies. For female chickens, brooding frequency is most considered in lowland (48.3%) and midland (37%) unlike in highland where age at first egg (47.1%) is prioritized. This study can be the base to design the breeding strategy of the chicken population in the study sites and beyond. Key words: Agro-ecology, breeding objectives, effective population, farmer preference, inbreeding coefficient, local chickens.

A predatory mite as potential biological control agent of Diaphorina citri

Diaphorina citri Kuwayama (Hemiptera: Liviidae) is a vector of the bacteria that cause Huanglongbing, the fatal disease threatening citriculture worldwide. One of the most important management methods is the control of D. citri with pesticides, but their intensive use causes development of resistance and pollution. An alternative method is therefore necessary to manage this vector-pathogen system. The generalist predatory mite Amblyseius herbicolus Chant (Acari: Phytoseiidae) can be found on citrus and orange jasmine plants, important hosts of D. citri in Brazil. Here we show that this phytoseiid can reproduce and develop on D. citri eggs. The predation rate was higher on D. citri eggs collected from plants in the field than on eggs from small plants from a laboratory rearing. Yet the predator preferred eggs from the laboratory. This may indicate that the higher predation rate of eggs from the field served to compensate for these eggs being of lower nutritional quality. This was confirmed with a series of experiments with limited numbers of eggs. We conclude that Amblyseius herbicolus is a potential biological control agent of D. citri, and its performance and control may be affected by the quality of the host plant.

Evaluation of a philic egg-consumption predatory thrips Scolothrips takahashii for control of the citrus red mite Panonychus citri

Panonychus citri is a major pest mite that is of great economic importance in most citrus orchards in China. Utilizing native predatory natural enemies is one of the useful biological control strategies to maintain pest population below the level where damage occurs for an extended period of time. Although a handful of pesticides and predatory natural enemy species have proven effective on the integrated control of the citrus red mite, they are not hard-hitting tactics for control of the P. citri eggs due to the protection of egg-shell. This study evaluated the potential of a native species of philic egg-consumption predatory thrips, Scolothrips takahashii, for control of P. citri in southwestern Chinese citrus orchards. An age-stage, two sex life table of S. takahashii was constructed, showing this predatory thrips could develop and reproduce successfully when fed on all stages of P. citri. All the functional responses of S. takahashii adult males and females on different stages of P. citri fit the Holling II disc equation, whereas this predatory thrips preferred eggs of P. citri significantly more than their larvae or nymph. Mutual interference results indicated that the searching efficiency and predation rate of S. takahashii decreased significantly with increased predator densities when supplied with sufficient P. citri eggs. Overall, this study indicated the potential of S. takahashii as a biological control agent of P. citri and helped to characterize the role of native predatory thrips in pest mite management.

Schistosome migration in the definitive host.

Schistosomes are parasitic blood flukes that infect >200 million people around the world. Free-swimming larval stages penetrate the skin, invade a blood vessel, and migrate through the heart and lungs to the vasculature of the liver, where maturation and mating occurs. From here, the parasite couples migrate to their preferred egg laying sites. Here, we compare and contrast what is known about the migration patterns within the definitive host of the three major species of human schistosome: Schistosoma mansoni, S. japonicum, and S. haematobium. We conclude that intravascular schistosomes are inexorable colonizers whose migration and egg laying strategy is profligate; all three species (and their eggs) can be found throughout the mesenteric venules, the rectal venous plexus, and, to a greater or lesser extent, the urogenital venous plexuses. In addition, it is common for parasite eggs to be deposited in locations that lack easy access to the exterior, further demonstrating the relentless exploratory nature of these intravascular worms.

Biologi, neraca hayati, dan pemangsaan Cryptolaemus montrouzieri Mulsant (Coleoptera: Coccinellidae) pada Paracoccus marginatus Williams & Granara de Willink (Hemiptera: Pseudococcidae)

Kutu putih pepaya, Paracoccus marginatus Williams & Granara de Willink (Hemiptera: Pseudococcidae), adalah hama asing invasif yang terdeteksi untuk pertama kalinya di Indonesia pada tahun 2008. Salah satu musuh alami yang umum ditemukan adalah kumbang predator Cryptolaemus montrouzieri Mulsant (Coleoptera: Coccinellidae). Penelitian ini bertujuan untuk menentukan parameter biologi dan neraca hayati serta pemangsaan C. montrouzieri pada P. marginatus. Pengamatan biologi dan neraca hayati serta pemangsaan dilakukan dengan menempatkan predator C. montrouzieri di dalam cawan Petri yang berisi kutu putih. P. marginatus. Hasil penelitian menunjukkan bahwa rataan masa inkubasi telur C. montrouzieri adalah 4,35 hari. Perkembangan larva instar-1, instar-2, instar-3, dan instar-4 secara berurutan berlangsung 4,23; 4,21; 5,84; dan 5,93 hari. Prapupa berlangsung 1,95 hari dan pupa 7,55 hari. Masa hidup imago jantan adalah 51,34 hari, sedangkan betina 83,39 hari. Jumlah telur yang diletakkan oleh satu imago betina rata-rata 198,49 butir. Laju reproduksi bersih (Ro) 117,11 individu/betina/generasi, laju pertambahan intrinsik (rm) 0,073 individu/betina/hari, rataan masa generasi (T) 64,776 hari, masa penggandaan (Dt) 9,426 hari, dan laju pertambahan terbatas (λ) adalah 1,076 per hari. Larva instar-4 C. montrouzieri merupakan fase yang paling rakus, dengan rataan jumlah telur, nimfa instar-1, instar-2, instar-3, dan imago betina kutu putih yang dimangsa per hari berturut-turut 188,0 butir; 53,4; 44,0; 26,8; dan 15,6 individu. Indeks preferensi Manly menunjukkan bahwa larva dan imago C. montrouzieri lebih memilih telur dan nimfa instar-1 P. marginatus dibandingkan dengan fase mangsa lainnya. Hasil penelitian mengindikasikan potensi yang tinggi dari C. montrouzieri dalam pengendalian hayati P. marginatus.

Host Preferences of Telenomus podisi (Hymenoptera: Scelionidae): Parasitism on Eggs of Dichelops melacanthus, Euschistus heros, and Podisus nigrispinus (Hemiptera: Pentatomidae).

Successful biological control requires detailed knowledge about host preferences of the released parasitoid, because the presence of alternative hosts may affect the control of the target pest. The objective of this work was therefore to evaluate host preferences of Telenomus podisi Ashmead among the eggs of three stink bug species: Dichelops melacanthus Dallas, Euschistus heros Fabricius, and Podisus nigrispinus Dallas (Heteroptera: Pentatomidae). Three independent experiments were carried out to study host preferences among the following: (1) E. heros, D. melacanthus dallas, and P. nigrispinus (bioassay 1); (2) E. heros and D. melacanthus (bioassay 2); and (3) D. melacanthus and P. nigrispinus (bioassay 3). A single bioassay (bioassay 4) was carried out to evaluate the egg size of E. heros, D. melacanthus, and P. nigrispinus. Two more bioassays were carried out: bioassay 5 to study the biological characteristics of T. podisi reared on E. heros, D. melacanthus, and P. nigrispinus eggs, and bioassay 6 to study the morphological characters of T. podisi reared on those different host eggs. Overall, T. podisi consistently preferred eggs of D. melacanthus to those of the other studied hosts, due to probably their better nutritional value; hypothesis that is supported by the fast T. podisi development and bigger parasitoids when reared on D. melacanthus and P. nigrispinus eggs. This allows suggesting that neither pre-imaginal conditioning nor associative learning nor α-conditioning are relevant to T. podisi parasitism. Thus, E. heros eggs could be successfully used for mass rearing of this parasitoid for successive generations since it would not affect its parasitism on other species of the Pentatomidae family in the field.

Patterns and causes of oviposition in monarch butterflies: Implications for milkweed restoration

Effective habitat restoration requires an understanding of species habitat preferences and the associated mechanisms driving those preferences. We examined the patterns and causes of oviposition preference in the monarch butterfly, a rapidly declining species, in southwestern Ontario at both landscape and milkweed patch spatial scales. Additionally, we measured the abundance of invertebrate predators, parasitoids and parasites across these same spatial scales. Oviposition preference was dependent on both the size of the milkweed patch and the density of milkweed within the patch, as well as landscape type. Small (<16m2), low-density (0.1–2 milkweed per m2) milkweed patches in agricultural landscape had the highest egg density compared to all types of milkweed patches in non-agricultural and roadside landscapes. Medium-sized patches had the highest predator abundance. Variation in the abundance of parasitoids, and occurrence of parasites of monarch eggs and larvae did not appear to coincide with preferred egg laying habitats. Our results suggest that investing heavily in milkweed restoration in roadside habitats should be done cautiously. Instead, a better strategy may be for managers to develop incentive programs with landowners to plant and maintain milkweeds in agricultural landscapes, which could complement other pollinator initiatives or ecosystem service programs in agricultural landscapes that focus on increasing nectar availability. Our results have important implications for restoring milkweed as an approach to counteract monarch butterflies declines.

&lt;strong&gt;Effects of &lt;em&gt;Wolbachia&lt;/em&gt; infection in &lt;em&gt;Tetranychus urticae&lt;/em&gt; (Acari: Tetranychidae) on predation by &lt;em&gt;Neoseiulus cucumeris&lt;/em&gt; (Acari: Phytoseiidae)&lt;/strong&gt;

Abstract Wolbachia are endosymbiotic bacteria that are widely distributed in arthropods. The bacteria cause reproductive disorders and affect fitness-related traits of their hosts. The generalist predatory mite Neoseiulus cucumeris(Oudemans) (Acari: Phytoseiidae) is a cosmopolitan species commonly used as a biological control agent for mites. Here we investigated the effect of Wolbachia infection in the prey, Tetranychus urticae, on predation by N. cucumeris by using both functional response tests (effect of prey egg density on predation) and choice and no-choice tests. The rate of egg consumption decreased with increasing egg density for both infected and uninfected eggs (Type II responses). In a no-choice test, N. cucumeris consumed approximately equal numbers of infected and uninfected eggs, nymphs and adults but consumed fewer infected larvae than uninfected larvae. In the first choice test, different developmental stages of T. urticae were provided, N. cucumeris preferred eggs and larvae over nymphs ...

Predation of calanoid copepods on their own and other copepods’ offspring

Predation of eggs and nauplii by adult copepods is often used to explain unexpected death rates in population dynamics studies, but the phenomenon has been rarely investigated or quantified. Therefore, we studied the predatory feeding of adult females (Acartia clausi, Centropages hamatus, Centropages typicus, and Temora longicornis) on their own and other species’ eggs and young nauplii with different densities of single animal-prey, mixtures of animal-prey and in the presence of diatoms. All species preyed on eggs and nauplii of their own and all other species. Maximal egg predation varied between 7 and 64 eggs fem−1 day−1. Ingestion of Centropages spp. eggs was lowest, potentially due to the spiny egg surface. Maximal feeding rates on nauplii ranged from 5 to 45 nauplii fem−1 day−1. T. longicornis preferred eggs, when eggs and nauplii were offered together at the same densities, and the other predators selected for nauplii. At a diatom concentration of 60 μg C l−1 predation on eggs by C. typicus was higher than without algae, whereas A. clausi and T. longicornis did not change their uptake of eggs. Feeding on nauplii in the presence of diatoms was again enhanced in C. typicus, and unaffected in A. clausi and C. hamatus. T. longicornis reduced its feeding on nauplii in the presence of diatoms. Calculated predation rates, using field abundances of predators and prey, suggest that predation of copepods on their own young stages may account for ca. 30 % of total mortality of young stages in North Sea copepod populations.

Indonesia

Kanzawa spider mite (KSM), Tetranychus kanzawai Kishida (Acari: Tetranychidae) is an important pest on many crops in Indonesia. Generally, farmers use acaricide to control this mite, which may cause negative side effects. One of the alternative control methods is the use of predatory mite. This research was done to determine prey preference and functional response of predatory mite Neoseiulus californicus (Acari: Phytoseiidae) on several life stages of KSM. Experiments were conducted under laboratory conditions. N. californicus were supplied with nymphs and adults of KSM to know its preference. N. californicus were also supplied with KSM eggs at several densities to know its functional response. Adult females and deutonymphs of N. californicus preferred KSM eggs than nymphs as their prey. The number of eggs consumed by adult females and deutonymphs N. californicus increased with the increase of prey density. The number of eggs laid by adult females of N. californicus increased with the increase of prey density. Searching time of the predator became faster with the increase of prey density. N. californicus showed cannibalism under low density of prey. Key words: Neoseiulus californicus , functional response, prey preference

Amazon poison frogs (Ranitomeya amazonica) use different phytotelm characteristics to determine their suitability for egg and tadpole deposition

Parents have to assess the multivariate characteristics of their reproductive sites to maximize their reproductive success through offspring performance. In addition, they may provide care to ensure optimal performance of their offspring. In poison frogs it has been identified that ecological characteristics of reproductive sites may underlie transitions in the involvement of parental sexes in care for offspring. To elucidate the ecological factors that may drive these transitions, it is important to understand which characteristics poison frogs use to assess the quality of their reproductive site. We studied the use of small water bodies in leaf axils of bromeliads, phytotelmata, for egg and tadpole deposition by Amazon poison frogs (Ranitomeya amazonica). We compared phytotelm quality characteristics for preferred egg and tadpole deposition sites and used two choice tests with plastic cups to study the causal relationship with tadpole deposition for the identified characteristics. The differences among quality characteristics of deposition sites were largest among bromeliad species, and for egg or tadpole deposition different bromeliad species were preferred. However, males were also selective in the leaf axils within a bromeliad species that they used for egg or tadpole deposition. Eggs were deposited in small, resource limited water bodies that were close to the forest floor. Tadpoles were deposited in leaf axils holding resource-rich phytotelmata with larger water volumes. Preference of detritus containing water over clear water in choice tests confirmed that Amazon poison frogs assess quality of their tadpole deposition sites on food availability. We conclude that preference for large water volume and resource rich phytotelmata plays an important role in determining male involvement in parental care and speculate that distribution of preferred resources may bring about selection on female involvement in parental care.

Life table and some feeding features of Nephus kreissli fed on Planococcus ficus

In this study certain biological and prey consumption features of the predator of mealybug, namely Nephus kreissli Fursch & Uygun (Coleoptera: Coccinellidae), fed on vine mealybug Planococcus ficus (Signoret) (Hemiptera: Pseudococcidae), were determined under the laboratory conditions. Experiments were performed in the acclimatized room under 28 ± 1°C, 60 ± 10% r.h. and a photoperiod of 16:8 h(L:D) conditions. To determine the biological features of the coccinellid, predator individuals were continuously observed from egg stage to end of adult stage. The development, survival and fecundity of N. kreissli were determined and all the measured data were recorded daily. The total development time from egg to the eclosion of adult stage was determined as 31.6 ± 0.4 days. The lifespan of males and females was 66.0 ± 3.8 and 65.8 ± 3.5 days, respectively; and a single female laid 122.6 eggs. The raw data related to life history were analyzed by using the age-stage, two-sex life table. The intrinsic rate of increase, the net reproductive rate, and the mean generation time were 0.0709 ± 0.0036 d−1, 53.1 ± 9.5 offspring and 55.8 ± 1.3 days, respectively. The first and second instars of N. kreissli preferred egg stages of P. ficus to other stages of mealybug. On the other hand, third and fourth instars and adult predators preferred the second and third instar nymphs and adult females of the prey. It was determined that the egg consumption of N. kreissli increased with the development of larval stages, and that the highest consumption was recorded in its fourth instar.

A quantified ethogram for oviposition behavior and oviposition preference in the hemipterophagous butterfly Spalgis epius (Westwood) (Lepidoptera: Lycaenidae)

In this study, we examined the oviposition behavior and preference of Spalgis epius, a potential predator of mealybug crop pests. An ethogram of oviposition behavior was constructed based on observations made in an oviposition cage. Ovipositional behavioral acts were catalogued and separated into two behavioral repertoires: searching and egg laying. Gravid females of S. epius oviposited similar numbers of eggs on three mealybug species. Females preferred eggs and adults to nymphs of mealybugs for oviposition. Among three species of mealybugs attended by ants, females laid fewer eggs in the mealybug mass attended by Oecophylla smaragdina than on mealybugs attended by Tapinoma melanocephalum and Camponotus variegatus. Females preferred mealybug masses already containing conspecific eggs to mealybug masses containing conspecific larvae or Cryptolaemus montrouzieri larvae for egg deposition. Gravid females laid larger numbers of eggs under bright sunlight than in diffused sunlight or shade. The results of this study showed that S. epius can effectively attack any species of mealybugs, avoid intra- and interspecific competition, and co-exist with some species of ants attending mealybugs. With the knowledge of these behaviors, this predator can be effectively utilized as a major biological control agent of mealybugs.

Egg Laying Decisions in Drosophila Are Consistent with Foraging Costs of Larval Progeny

Decision-making is defined as selection amongst options based on their utility, in a flexible and context-dependent manner. Oviposition site selection by the female fly, Drosophila melanogaster, has been suggested to be a simple and genetically tractable model for understanding the biological mechanisms that implement decisions [1]. Paradoxically, female Drosophila have been found to avoid oviposition on sugar which contrasts with known Drosophila feeding preferences [1]. Here we demonstrate that female Drosophila prefer egg laying on sugar, but this preference is sensitive to the size of the egg laying substrate. With larger experimental substrates, females preferred to lay eggs directly on sugar containing media over other (plain, bitter or salty) media. This was in contrast to smaller substrates with closely spaced choices where females preferred non-sweetened media. We show that in small egg laying chambers newly hatched first instar larvae are able to migrate along a diffusion gradient to the sugar side. In contrast, in contexts where females preferred egg laying directly on sugar, larvae were unable to migrate to find the sucrose if released on the sugar free side of the chamber. Thus, where larval foraging costs are high, female Drosophila choose to lay their eggs directly upon the nutritious sugar substrate. Our results offer a powerful model for female decision-making.

Evidence for an African cluster of human head and body lice with variable colors and interbreeding of lice between continents.

BackgroundHuman head lice and body lice have been classified based on phenotypic characteristics, including geographical source, ecotype (preferred egg laying site hair or clothes), shape and color. More recently, genotypic studies have been based on mitochondrial genes, nuclear genes and intergenic spacers. Mitochondrial genetic analysis reclassified lice into three genotypes (A, B and C). However, no previous study has attempted to correlate both genotypic and phenotypic data.Materials and MethodsLice were collected in four African countries: Senegal, Burundi, Rwanda and Ethiopia and were photographed to compare their colors. The Multi-Spacer-Typing (MST) method was used to genotype lice belonging to the worldwide Clade A, allowing a comparison of phenotypic and genotypic data.ResultsNo congruence between louse color and genotype has been identified. Phylogenetic analysis of the spacer PM2, performed including lice from other sources, showed the existence of an African cluster of human lice. However, the analysis of other spacers suggested that lice from different areas are interbreeding.ConclusionsWe identified two geotypes of Clade A head and body lice including one that is specifically African, that can be either black or grey and can live on the head or in clothing. We also hypothesized that lice from different areas are interbreeding.

Application of a Gene-Based Population Dynamics Model to the Optimal Egg Size Problem: Why Do Bivalve Planktotrophic Eggs Vary in Size?

ABSTRACT The presumption is that egg quality influences larval survival and that egg size influences egg quality. Thus, larger eggs should be favored by selection. Counterweighing the tendency for egg size to increase is the number of eggs that can be produced if egg size remains small. We examine how egg size and egg number counterbalance in Crassostrea oysters, resulting in an average egg size near 50 µm. Simulations imposing a diversity of ranges in larval survivorship—from little advantage for large eggs relative to small eggs to a great advantage—yield some anticipated outcomes in which genotypes generating larger eggs are favored. In other simulations, however, genotypes generating smaller eggs became increasingly common. In these cases, egg size declines, as does the likelihood of survival of individual larvae: the antithesis of expectation. Few simulations identify preferred egg sizes near the size typically observed, suggesting that, under most field conditions, a selective advantage exists for s...