Oviposition Patterns Research Articles

An entomocentric view of the Janzen–Connell hypothesis

In 1987, in the first issue of Conservation Biology, Edward O. Wilson wrote about the “little things that run the world” – the importance and conservation of insects (Wilson, 1987). Readers of Insect Conservation and Diversity will no doubt be very familiar with the concept. Sadly, however, this perception is not as widely shared among the rest of the scientific community as it should be, and insects are still comparatively neglected as a prime focus of scientific investigations.

Tetranychus urticae changes its oviposition pattern in the presence of the predatory mites, Phytoseiulus persimilis and Typhlodromus bagdasarjani

Oviposition behaviors in herbivorous mites are affected by several factors i.e. food availability for juveniles and reduced predation risks. We used the twospotted spider mite, Tetranychus urticae Koch (Tetranychidae) to find out whether the previous presence of specialist/ generalist phytoseiid predator individuals, Phytoseiulus persimilis Athias-Henriot/ Typhlodromus bagdasarjani Wainstein & Arutunjan (here, direct effect) or their previous odour perception by prey (here, indirect effect) would affect T. urticae oviposition strategies. Tetranychus urticae female individuals were placed on a leaf disc in a plastic container with predators either on the same disc (direct presence of predator) or on the second disc (receiving odours related to a predator) in the same container. Getting experienced, the prey individuals transferred to the oviposition container to their oviposition pattern parameters get recorded. The ovipositing T. urticae were monitored in two experimental situations: 1. Receiving odours related to the predator- prey interaction from the second leaf disc in the same oviposition container during their oviposition period, and 2. Receiving no odour. Our results showed that when T. urticae females perceived the predator presence in their first container (with either predator species, both direct and indirect effect), they reduced their total egg distances, oviposition rates and oviposition periods significantly regardless of receiving odours related to prey-predator interactions during experiment. Receiving odours during oviposition, T. urticae females decreased their pairwise egg distances in at least 4 and at most 6 pairs of eggs, while when odours were absent during oviposition, the distances decreased in at least 2 and at most 3 pairs of eggs. The direct presence of P. persimilis reduced the prey oviposition period significantly more than that when T. bagdasarjani was present. The spider mites oviposition rate reduction was obviousely more than that in the presence of T. bagdasarjani. The different effects of predator species on T. urticae egg distances were discussed.

Multi‐scale oviposition site selection in two mosquito species

1. In organisms characterised by complex life cycles, habitat selection often occurs at multiple spatial scales. For instance, female mosquitoes searching for an appropriate aquatic habitat to oviposit their eggs should also consider the characteristics of the terrestrial landscape in which it is embedded.2. In this study, a field experiment was conducted to test for multi‐scale oviposition site selection in two mosquito species. Artificial pools were placed in two adjacent landscapes, olive plantations and a citrus orchard, mainly differing in their blooming periods and nectar availability. Pools were organised in three pairs: predatory caged fish were present in both pools, in one pool, or in none.3. Early during the season, most of the egg rafts were laid by Culiseta longiareolata females in pools located within the blooming citrus orchard. When blooming shifted to the olive plantation, C. longiareolata become opportunistic. Culex pipiens females appeared later on during the season, when egg rafts of C. longiareolata were scarce, and they exhibited a higher selectivity to the olive plantation, although its blooming ended. In addition, the selectivity of C. pipiens to fish‐free pools was stronger than that of C. longiareolata.4. Culex pipiens was more selective, possibly due to its high dispersal ability, which can lower movement cost and enhance the ability to gather environmental information. A trade‐off among gonotrophic cycles, combined with a shorter breeding season and limited recognition ability of the predatory fish may have reduced C. longiareolata selectivity. These differential oviposition patterns can strongly affect the population and community dynamics of both species.

Termination of Diapause in the Boll Weevil (Coleoptera: Curculionidae).

The boll weevil, Anthonomus grandis grandis Boheman (Coleoptera: Curculionidae), is a major pest of cotton (Gossypium spp. (Malvales: Malvaceae)) in Mexico, South America, and South Texas in the United States. The ability of the boll weevil to survive extended cotton-free periods has been key to its persistence as a pest despite intensive control efforts. However, the mechanism facilitating survival has been subject to debate. Whereas adult diapause has long been considered the principal survival mechanism, some authors have characterized the dormancy as a quiescence. We induced dormancy in the weevil and examined whether food type, enforced starvation, or induced flight influenced termination of the dormancy. Providing dormant adult weevils a diet favoring reproduction for 7-14 d prompted a modest termination response in female weevils and virtually no response in males. Some weevils starved ≥21 d resumed reproduction after exposure to a favorable diet, but most weevils remained dormant. Induced flight followed by exposure to a favorable diet prompted >50% of the weevils to terminate the dormancy. Patterns of feeding and oviposition were also useful in interpreting the termination response. These results indicate that the dormancy exhibited by the weevil is a diapause of variable intensity rather than a quiescence. A conceptual model recognizing population heterogeneity in diapause induction and intensity is consistent with reports of host-free survival and accommodates perceived differences in boll weevil ecology among temperate, subtropical, and tropical regions. This model provides a framework that will be valuable to research, management, and eradication efforts in the tropics and subtropics.

Observing the devastating coffee berry borer (Hypothenemus hampei) inside the coffee berry using micro-computed tomography

The coffee berry borer is the most devastating insect pest of coffee throughout the world. The insect spends most of its life cycle inside the coffee berry, which makes it quite difficult to observe its behaviour. Micro-computed tomography (micro-CT) was used to observe all developmental stages of the coffee berry borer inside coffee berries (Coffea canephora). An interesting oviposition pattern involving a sequential placement of eggs starting in the periphery of the seed and moving inwards was observed. Micro-CT should be useful in elucidating unknown life history aspects of other seed-feeding bark beetles as well as of bark and ambrosia beetles in general.

Recording and reproducing the diurnal oviposition rhythms of wild populations of the soft- and stone- fruit pest Drosophila suzukii.

Drosophila suzukii is a horticultural pest on a global scale which causes both yield and economic losses on a range of soft- and stone-fruit. Tackling this pest is problematic but exploiting behavioral rhythms could increase the impact of control. To do this, a better understanding of behavioral patterns is needed. Within this study we aimed to investigate rhythms in reproductive behavior of wild D. suzukii under natural conditions in the field. Environmental parameters were also recorded to decipher how they influence these rhythms. Assays were then performed on laboratory cultures, housed under artificial conditions mimicking the temperature and light cycles, to see if these patterns were reproducible and rhythmic. We were able to promote field like oviposition patterns within the laboratory using realistic temperature and light cycles regardless of variations in other factors including substrate, humidity, and lighting type. Locomotion activity was also recorded under these mimicked conditions to identify how this behavior interacts with oviposition rhythms. Both our field and laboratory assays show that oviposition behavior is likely under the control of the circadian clock and primarily occurs during the day. However, consistent with prior reports we observed that these patterns become crepuscular when day-time temperature peaks exceeded 30°C. This was also found within locomotion rhythms. With an increased understanding of how these behaviors are influenced by environmental conditions, we highlight the importance of using realistic temperature and light cycles when investigating behavioral patterns. From an increased understanding of D. suzukii behavior we increase our ability to target the pest in the field.

Bio-ecology and management of spiraling whitefly, Aleurodicus dispersus Russell through insecticides : A review

Spiraling whitefly, Aleurodicus dispersus Russell is the most devastating pest of many vegetables, fruits and ornamental trees with a characteristic spiraling pattern of oviposition on the underside of leaves. Heavy colonization of whitefly may cause a serious indirect damage to the crop due to honeydew excretion on the leaves or on fruit surfaces which encourages growth of the sooty mould fungus and in turn affects the yield both quantitatively and qualitatively. Whiteflies develop rapidly in warm weather, and populations can build up quickly in situations where natural enemies are destroyed and weather is favourable. Thus, whiteflies are difficult to manage once their populations have reached high levels. Further, repeated applications of insecticides can lead to development of resistance. Thus, for its sustainable management, the spray interventions should be taken at low levels of whitefly population. In this paper, a brief account of its hosts, biology and damage is dealt along with its management through insecticides. Among the different insecticides tested against spiraling whitefly, the least LC50 was recorded by flubendiamide 480 SC (34.55 ppm) and emamectin benzoate 5 SG (39.14 ppm) against eggs, by spinosad 45 SC with 39.78 and 106.62 ppm against nymphs and adults, respectively.

Factors affecting the egg-laying pattern of Forficula auricularia (Dermaptera: Forficulidae) in three climatologically different zones of North America

AbstractEgg-laying patterns of the European earwig, Forficula auricularia Linnaeus (Dermaptera: Forficulidae), from three climatologically different areas; Montréal, Québec, Canada, Vancouver, British Columbia, Canada, and San Francisco, California, United States of America; were compared in laboratory. Three different egg-laying patterns were observed. Among the biotic parameters studied; previtellogenic follicular atresia, number of oocytes per ovariole at imaginal moult, female life expectancy, and ovarian activity explained female successful responses to local weather conditions. Follicular atresia, combined with a low number of oocytes, impeded oviposition in a low percentage of females from Montréal. It also impedes the production of a third brood in the Vancouver population, and of a fourth brood in the San Francisco population. Both female life expectancy and length of ovarian activity also had a significant impact on the oviposition pattern in the three climatic regions. Under the cold temperate climate of the Montréal area, only one brood was produced due to the short period of female fertility. Longer period of fertility and life expectancy enabled females to produce two broods in the milder temperate climate of Vancouver, and three broods in the San Francisco climate. Our results strongly suggest an exaptation enabling the native European populations of F. auricularia to adapt successfully in North America.

Dim artificial light at night affects mating, reproductive output, and reactive oxygen species in Drosophila melanogaster.

Humans are lighting the night-time environment with ever increasing extent and intensity, resulting in a variety of negative ecological effects in individuals and populations. Effects of light at night on reproductive fitness traits are demonstrated across taxa however, the mechanisms underlying these effects are largely untested. One possible mechanism is that light at night may result in perturbed reactive oxygen species (ROS) and oxidative stress levels. Here, we reared Drosophila melanogaster under either dim (10lx) light or no light (0lx) at night for three generations and then compared mating and lifetime oviposition patterns. In a second experiment, we explored whether exposure to light at night treatments resulted in variation in ROS levels in the heads and ovaries of six, 23- and 36-day-old females. We demonstrate that dim light at night affects mating and reproductive output: 10lx flies courted for longer prior to mating, and female oviposition patterns differed to 0lx females. ROS levels were lower in the ovaries but not heads, of 10lx compared with 0lx females. We suggest that reduced ROS levels may reflect changes in ovarian physiology and cell signaling, which may be related to the differences observed in oviposition patterns. Taken together, our results indicate negative consequences for invertebrates under more stressful, urban, lit conditions and further investigation into the mechanisms driving these changes is warranted to manage invertebrate communities in a brighter future.

Sublethal effects of two reduced-risk insecticides: when the invasive ladybeetle is drastically affected, whereas the indigenous not

Chlorantraniliprole and novaluron, two reduced-risk insecticides (IRRs), are currently used to control codling moth (Cydia pomonella) in apple orchards in southeastern Canada. Reproduction of Harmonia axyridis (Pallas), an invasive ladybeetle, and the indigenous Coleomegilla maculata DeGeer, both important generalist predators, might be compromised after exposure of adults to these IRRs. The aim of the study was to compare the effects of chlorantraniliprole and novaluron on fecundity and fertility between the two ladybeetles in a laboratory setting. Reproductive mates were given chlorantraniliprole- or novaluron-treated prey for 24 h, and reproductive performance was followed during 15 days. Chlorantraniliprole did not affect reproduction of ladybeetles. However, novaluron-reduced fecundity, egg hatch, and fertility of the invasive ladybeetle H. axyridis, by 29, 43, and 78.7%, respectively, contrasting with no significant effect on the indigenous C. maculata. Additionally, H. axyridis oviposition pattern was altered by the same insecticide. This resulted in more egg masses containing fewer eggs, compared to the control. No such changes were detected for C. maculata. Chlorantraniliprole does not disturb reproduction of H. axyridis or C. maculata. Treatments of novaluron should have an important effect on populations of the invasive H. axyridis, and consequently on the impact of the invader on native ladybeetle species and on its dominance, and finally potentially on biocontrol services provided by the assemblage of ladybeetles.

Life history parameters of the microtype parasitoid fly Pales pavida (Diptera: Tachinidae), and effects of host age and number of eggs ingested by host on parasitism success

ABSTRACTWith the aim of developing better procedures for rearing the microtype tachinid fly Pales pavida (Meigen), we performed ecological studies in the laboratory using the natural host Mythimna separata (Walker), investigating larval development, mating behaviour, individual oviposition patterns and relationships between parasitisation and number of eggs ingested (NEI) per host. The host instar at the time of parasitoid egg ingestion significantly affected the development time of the immature parasitoid: development took longer when the hosts ingested eggs when at the fifth instar than at the sixth (last) instar. There was no difficulty obtaining mated females in the laboratory when day 0–1 female flies were kept with day 2–4 males. Mean lifetime fecundity was 5805 ± 568 eggs per female. Daily rates of oviposition by individual females varied widely; the greatest number of eggs laid in a day was exactly 1700. When the NEI by day 1 fifth instars or day 0 or 3 last instars was 1, 3, 6 or 10, the parasitisation percentage tended to increase with increasing NEI, although it did not differ significantly between NEI 6 and 10. Therefore, the percentage adult emergence per egg ingested decreased from NEI 6 to 10, particularly in the case of last instars. Using day 0 last instars, with six eggs ingested per host, should increase parasitisation rates and shorten the development time of the parasitoid for rearing.

Biology of Aganaspis daci (Hymenoptera: Figitidae), parasitoid of Ceratitis capitata (Diptera: Tephritidae): Mode of reproduction, biological parameters and superparasitism

Biological parameters of parasitoid wasps have a decisive effect on their effective performance as biological control agents. The mode of reproduction, several mating-dependent biological parameters (such as longevity, fertility, percentage parasitism, induced mortality and population reduction) as well as superparasitism of the parasitoid Aganaspis daci (Weld) infesting larvae of the medfly Ceratitis capitata (Wiedemann) were assessed under laboratory conditions. The results indicated an arrhenotokous haplodiploid mode of reproduction, with unmated females producing only males and mated females producing a female-biased offspring (♀♀/(♀♀+♂♂) = 0.73) ratio from the first day of life. Additionally, positive mating status showed a significant negative effect on longevity (14–22 days), but no significant differences on fertility, percentage parasitism, induced mortality or population reduction between mated and unmated females. A strong effect of the age of females on fertility and percentage of parasitism was also found, with both decreasing with increasing female age and a similar oviposition pattern for mated and unmated females. Our findings showed the occurrence of superparasitism in this species, with a significant negative effect of host abundance and a significant positive effect of parasitoid (conspecific females) abundance on superparasitism rate. The existence of self-superparasitism was confirmed for females acting alone, whilst female aggregation led to a higher intensity (up to eight eggs/host pupa) and percentage of, presumably, conspecific superparasitism. The information reported here on several biological aspects of A. daci infesting C. capitata supports the use of this parasitoid in biological control programmes against medfly and highlights the importance of several factors, such as the sex ratio or the parasitoid/host ratio under rearing and field conditions, when planning mass production and field releases of this parasitoid.

Direct and plant trait‐mediated effects of the local environmental context on butterfly oviposition patterns

Variation in the intensity of plant–animal interactions over different spatial scales is widespread and might strongly influence fitness and trait selection in plants. Differences in traits among plant individuals have been shown to influence variation in interaction intensities within populations, while differences in environmental factors and community composition are shown to be important for variation over larger scales. However, little is still known about the relative importance of the local environmental context vs. plant traits for the outcome of interactions within plant populations. We investigated how oviposition by the seed‐predator butterfly Phengaris alcon on its host plant Gentiana pneumonanthe was related to host plant traits and to local environmental variation, as well as how oviposition patterns translated into effects on host plant fruit set. We considered the local environmental context in terms of height of the surrounding vegetation and abundance of the butterfly's second host, Myrmica ants. The probability of oviposition was higher in plants that were surrounded by lower vegetation, and both the probability of oviposition and the number of eggs increased in early‐flowering and tall plants with many flowers in the three study populations. Flowering phenology, shoot height and flower production were, in turn, related to higher surrounding vegetation. Myrmica abundance was correlated with vegetation height, but had no effect on oviposition patterns. Oviposition and subsequent seed predation by the caterpillars strongly reduced host plant fruit set. Our results show that plant–animal interactions are context‐dependent not only because the context influences the abundance or the behavior of the animal interactor, but also because it influences the expression of plant traits that affect the outcome of the interaction. The results also demonstrate that heterogeneity in environmental conditions at a very local scale can be important for the outcomes of interactions.

Ant-partners play a minor role on occurrence of the myrmecophilous butterfly Leptotes cassius in its host plant

Ant-related oviposition in facultatively myrmecophilous lycaenid butterflies is common, but not universal. In fact, our knowledge of ant-related oviposition in lycaenids is based on some common species (e.g., Rekoa marius, Allosmaitia strophius, Parrhasius polibetes), which limits generalizations about these systems. In this study, we experimentally investigated whether the oviposition pattern of the florivorous lycaenid Leptotes cassius was influenced by the presence of Camponotus ants and whether larvae were attended, rather than attacked, by ants. This might be evidence of myrmecophily. Both L. cassius and Camponotus ants occur on Bionia coriacea, an extrafloral nectaried legume shrub that grows in the Brazilian cerrado. Plants were randomly assigned to ant-present and ant-excluded treatments and were observed twice throughout the short reproductive season. Larvae of L. cassius were tended by ants, whose attendance was characterized by active antennation on the last body segments of the caterpillars. Therefore, Camponotus can be considered a partner of L. cassius. Lycaenid abundance was on average 1.9- and 1.21-fold higher in plants with ants in each sampling period, respectively, indicating a tendency of L. cassius to occur in plants with ants. Nonetheless, results were not statistically significant, suggesting that in this case ants are not a major cue for lycaenid oviposition. In many ant–lycaenid mutualisms, butterfly immatures benefit from reduced parasitism rates. However, no L. cassius immature, regardless of ant presence or absence, was parasitized. Furthermore, larvae may occur inside flower buds that may provide protection from natural enemies; thus, ants may not be required for immature protection.

Impact of Insecticides on Trichogramma Chilonis Parasitism and in the Oviposition Pattern of Large Cabbage Moth Eggs

Abstract This study determined the effects of key insecticides on Trichogramma chilonis parasitism in field trials. It showed that the number of large cabbage moth (LCM) eggs in Chinese cabbage was significantly reduced after application of AttackTM (p: 0.001) and EntrustTM (p: 0.00) but not after spraying with OrtheneTM (p: 0.09) and DipelTM (p: 0.485). Negative effects of insecticides were observed on the parasitism rate of T. chilonis and LCM egg masses, which were more likely to be only partially parasitised after an insecticide application. AttackTM and EntrustTM adversely affected T. chilonis parasitism rates of LCM eggs. However, the effect of OrtheneTM and DipelTMdid not significantly differ from each other and could be safer to the parasitoid since both reduced T. chilonis parasitism the least. The distribution of LCM eggs in the cabbage leaves was also affected by the insecticides; before insecticide application the majority of egg masses were concentrated in the upper surface of the foliage but after insecticide sprays most of the egg masses were found in the lower surface of the foliage. This study suggests that OrtheneTM and DipelTMhave no effect on the parasitism but DipelTM was found safer to the parasitoid and it could be considered for inclusion in IPM programmes that depend on T. chilonis parasitism of LCM.

Effect of the combined application of microencapsulated synthetic oviposition pheromone (MSP) with different larvicidal agents on the oviposition of Culex pipiens biotype molestus.

Attract-and-kill strategies, in which a behavior-modifying stimulus (e.g. a pheromone) is integrated with a pest control agent, have lately attracted increased interest for mosquito control. Previously, it was demonstrated that the polyurea microencapsulated synthetic oviposition pheromone 6-acetoxy-5-hexadecanolide (MSP) was sufficiently attractive to gravid females of Culex pipiens L. biotype molestus Førskal (Diptera: Culicidae) for a period of 40 days. Furthermore, it was shown that MSP could be effectively combined with the organophosphate temephos to achieve efficient mosquito control. In the present study, the effect of the combined application of MSP with commonly used larvicides on the oviposition response of Cx. p. biotype molestus females over time was investigated in two-choice oviposition bioassays. As larvicides, the insect growth regulator diflubenzuron and the bacterial insecticide spinosad were evaluated at their lowest recommended label dose, whereas temephos was used as a control. When MSP was applied in combination with diflubenzuron, the attractancy of MSP to gravid females was in all cases negatively affected, as fewer egg rafts were laid in pots treated with MSP and diflubenzuron compared with MSP alone. Spinosad did not reduce, but rather increased, the attractive effect of the oviposition pheromone at the beginning of the bioassay (at 2 days of ageing) when co-applied; however, the observed attractive effect was significantly reduced after 7 days of ageing and remained stable at the same level until the termination of the bioassay. Finally, the oviposition pattern of egg rafts laid on the pot with MSP and temephos was similar to that of egg rafts laid on the pot with MSP alone, showing that temephos did not significantly affect MSP activity. The results of the present study highlight the effects of the combined application of MSP with spinosad and diflubenzuron on the oviposition of gravid Cx. p. biotype molestus females, which in most cases eliminated the attractive effect of MSP. © 2017 Society of Chemical Industry.

Aedes aegypti (L.) mosquitoes in Trinidad, West Indies: longevity case studies.

Few laboratory and field studies have reported long survival periods for Ae. aegypti females and even fewer have designed experiments to characterize this important life history trait. This study was conducted under laboratory conditions to determine the number of blood meals taken by individual females, the number of eggs laid per individual female, the length of the gonotrophic cycle, and the duration of female survival. The results showed individual females oviposited between 670 and 1,500 eggs throughout their lifetimes, females undergoing large numbers of gonotrophic cycles and surviving up to 224 days. These results are discussed in the context of vector competence, unique alternating high and low oviposition patterns observed after week 14, and resource partitioning/allocation by older Ae. aegypti females after blood feeding.

Discrimination of infested cotton squares by females of Anthonomus grandis

The avoidance of infested squares of Gossypium hirsutum as oviposition substrate by females of Anthonomus grandis was studied following two approaches. First, the preference for oviposition in infested versus non-infested squares was studied in laboratory. Second, the distribution of ovipositions by A. grandis in nature was analyzed in cotton plots from Argentina. In addition, the consequences of multiple ovipositions were assessed in terms of emergence rate, adult weight and sex ratio. In the laboratory, the number of ovipositions was significantly higher in non-infested than in infested squares. Likewise, females were found to reject infested squares more frequently than non-infested squares. In the field, oviposition pattern fitted a uniform distribution for squares collected from the ground, while the distribution in squares sampled from the plant fitted random and uniform distributions. This suggests that oviposition decisions could be dynamic and change with the infestation conditions. Multiple ovipositions resulted in the elimination of competing larvae between L1 and L2 instars. The weight of the individual that develops to the adult stage was negatively affected by the level of larval competition, and the sex ratio deviated toward females. Our results suggest that females of A. grandis tend to avoid already infested squares. This behavior would allow reducing the levels of intraspecific competition, which we also found can seriously affect the development of their progeny. A deeper knowledge of the oviposition behavior of A. grandis could contribute to developing control methods against this important cotton pest.

Aggregated oviposition in Rhodnius prolixus, sensory cues and physiological consequences

Females of the haematophagous bug Rhodnius prolixus attach their eggs in clusters on substrates related to their hosts, such as nests or avian feathers. Because the hosts are an enormous food resource as well as potential predators, the choice of the site and pattern of oviposition could have an important adaptive value. Here we investigated proximate and a potential ultimate cause of this aggregated pattern of laid eggs. First, we studied proximal causes by analyzing the use of chemical or physical cues associated with aggregated oviposition in R. prolixus. For all terrestrial organisms there is a trade-off between exchange of respiratory gases and water loss. Particularly, insect eggs are highly susceptible to this trade-off because they do not obtain water from the environment, hence our second objective is to study the possible mechanisms involved in dehydration resistance in this species. Therefore we examined the dynamics of change in CO2 release rate (ṀCO2), and water loss rate (ṀH2O) in relation to embryo development as energetic demands increase, and tested the energetic or hygric efficiency hypothesis as a potential ultimate cause of aggregated oviposition. This hypothesis states that grouped eggs consume less energy or lose less water than equal numbers of isolated eggs, the latter being more susceptible to dehydration. Results indicated the use of physical external cues such as dummy eggs or edges of the oviposition substrates, but we did not find any chemical cues associated with the aggregated pattern of oviposition. There are no energetic or hygric benefits associated with egg’s aggregated pattern. However, when we analyzed the ṀCO2 and ṀH2O change in relation to embryo development, we found a fairly constant and low ṀH2O albeit a clear increase in ṀCO2, suggesting a tightly control of egg’s desiccation tolerance. This high resistance to desiccation coupled with a temporal strategy of hatching allows R. prolixus embryos to successfully develop and hatch under harsh environmental conditions.

Male-Biased Capture in Light Traps in Spodoptera exigua (Lepidoptera: Noctuidae): Results from the Studies of Reproductive Activities

Nocturnal insects show phototactic behavior. Interestingly, males are caught by light traps more often than females in many species. In the present study, the male-biased capture in light traps in the field was evaluated to test the hypothesis that male-biased capture was associated with the reproductive activities of Spodoptera exigua. During a 16-wk. period in 2011, a total of 5075 moths caught by light traps in the field revealed a significant male-biased capture. However, the sex ratio of the natural population was not significantly different from 1:1 from July to October 2011. The ratio of moths caught per hour by light traps showed that females were captured in the first half of the night, whereas the peak capture by light traps for males occurred in the second half of the night. Among the captured adults, the percentage of unmated females was significantly lower than that of the mated females and males. Experiments in the laboratory indicated that the time of activities for both sexes was consistent with the active patterns of oviposition and copulation. The percentage of flight-to-light of the unmated females was significantly lower than that of the mated females and males. Thus, the lower capture of the unmated females, which is associated with reduced positive phototactic responses of S. exigua, probably is one of the reasons resulting in the male-biased sex ratio in light traps.