Univoltine Insect Research Articles

Variation in Thermal Sensitivity of Diapause Development among Individuals and over Time Predicts Life History Timing in a Univoltine Insect.

AbstractPhysiological time is important for understanding the development and seasonal timing of ectothermic animals but has largely been applied to developmental processes that occur during spring and summer, such as morphogenesis. There is a substantial knowledge gap in the relationship between temperature and development during winter, a season that is increasingly impacted by climate change. Most temperate insects overwinter in diapause, a developmental process with little obvious morphological change. We used principles from the physiological time literature to measure and model the thermal sensitivity of diapause development rate in the apple maggot fly Rhagoletis pomonella, a univoltine fly whose diapause duration varies substantially within and among populations. We show that diapause duration can be predicted by modeling a relationship between temperature and development rate that is shifted toward lower temperatures compared with typical models of morphogenic, nondiapause development. However, incorporating interindividual variation and ontogenetic variation in the temperature-to-development rate relationship was critical for accurately predicting fly emergence, as diapause development proceeded more quickly at high temperatures later in diapause. We conclude that the conceptual framework may be flexibly applied to other insects and discuss possible mechanisms of diapause timers and implications for phenology with warming winters.

Diapause in Univoltine and Semivoltine Life Cycles.

Although it is generally more adaptive for insects to produce additional generations than to have longer life cycles, some insects produce one or fewer generations per year (univoltine or semivoltine life cycles, respectively). Some insects with the potential to produce multiple generations per year produce a univoltine life cycle in response to environmental conditions. Obligatory univoltine insects have a single long diapause or multiple diapauses in different seasons. Semivoltine insects have multiple diapauses in different years, a prolonged diapause for more than a year, or diapause controlled by a circannual rhythm. Diapause in these insects greatly varies among species both in the physiological mechanism and in the evolutionary background, and there is no general rule defining it. In this review, we survey the physiological control of univoltine and semivoltine insects' diapause and discuss the adaptive significance of the long life cycles. Although constraints such as slow development are sometimes responsible for these life cycles, the benefits of these life cycles can be explained by bet-hedging in many cases. We also discuss the effect of climate warming on these life cycles as a future area of research.

Topical Application of Synthetic Hormones Terminated Reproductive Diapause of a Univoltine Weed Biological Control Agent.

Simple SummaryYellow starthistle (Centaurea solstitialis) is an invasive annual plant that has infested multi-million ha in the western United States, causing multi-billion dollars of losses and management costs. The rosette weevil (Ceratapion basicorne) has recently been approved for biological control of this weed. However, this weevil reproduces only once a year, which hinders mass-rearing for release. Here, we tested whether insect hormones can break the reproductive diapause of female weevils. We found that applying two insect hormones, 20E and methoprene, can consistently terminate diapause of female weevils to enable them to lay eggs. Thus, topically applying insect hormones could be used to induce females to lay eggs at any time of year, which would permit rearing more than one generation per year. This could greatly increase the number of weevils produced per year in a mass-rearing program to accelerate the release of rosette weevils to help suppress yellow starthistle in the United States. These insects would revert to having one generation per year after release in synchrony with their host plant.Classical biological control is an important method for controlling invasive alien weeds. Univoltine insects can be highly effective biological control agents of annual weeds because they are well synchronized with their host plant. However, having only one generation per year makes it difficult and slow to multiply them in the laboratory for initial field releases. If it were possible to terminate reproductive diapause early, then we could rear multiple generations per year, which would greatly increase annual production. We used a recently approved biocontrol agent, Ceratapion basicorne (a univoltine weevil), for yellow starthistle (Centaurea solstitialis) as a model system to study the use of two insect hormones, 20-hydroxyecdysone (20E) and methoprene, to terminate reproductive diapause. Methoprene (1 μg applied topically) terminated reproductive diapause of female weevils, whereas doses of 0.0, 0.01 and 0.1 μg did not. The combination of methoprene and 20E had a stronger effect and induced an increase in eggs (1.51 ± 0.16 eggs/day, mean ± SE) compared with a methoprene only group (1.00 ± 0.13 eggs/day), and a control group (0.21 ± 0.04 eggs/day). Thus, topical application of these hormones should enable us to rear the weevil out of its normal season and produce more than one generation per year, which will increase productivity of mass-rearing it for field release. Once released in the field, the insect would continue as a univoltine agent that is well-synchronized with its host plant.

Low Temperature Duration and Adult Rearing Regimes Affect Eclosion of Rhagoletis indifferens (Tephritidae: Diptera).

Western cherry fruit fly, Rhagoletis indifferens Curran, is a quarantine pest of sweet cherries in the Pacific Northwest of the United States that overwinters as diapausing pupae. Eclosion responses of R. indifferens puparia to different low temperature durations and postdiapause conditions affect the pest status of the fly. Here, we determined the effects of holding R. indifferens puparia at 3°C for 0, 1, 2, 5, 10, 15, and 20 wk on adult eclosion times and rates at two simulated temperate and two simulated tropical climate treatments over 40 wk. When puparia were chilled 0, 1, or 2 wk, adult eclosion across the four climate treatments displayed a bimodal distribution with low eclosion at 3 wk and high eclosion at 23-35 wk. When puparia were chilled ≤ 10 wk, there was a weaker bimodal distribution. However, when puparia were chilled 15-30 wk, eclosion was more synchronous and occurred at 5-7 wk across the four postchill climate treatments. Eclosion was greater at a postdiapause temperature of 26°C than 23°C. Timing to 50% eclosion was faster at longer photoperiod (16:8 L:D) than shorter (12:12 L:D). The bimodality of eclosion in respect to the duration of low temperature exposure may be indicative of univoltine insect species with obligate diapause that may span over two seasons.

Variations in seasonal (not mean) temperatures drive rapid adaptations to novel environments at a continent scale.

The recent development of human societies has led to major, rapid, and often inexorable changes in the environment of most animal species. Over the last decades, a growing number of studies formulated predictions on the modalities of animal adaptation to novel or changing environments, questioning how and at what speed animals should adapt to such changes, discussing the levels of risks imposed by changes in the mean and/or variance of temperatures on animal performance, and exploring the underlying roles of phenotypic plasticity and genetic inheritance. These fundamental predictions, however, remain poorly tested using field data. Here, we tested these predictions using a unique continental-scale data set in the European earwig Forficula auricularia L., a univoltine insect introduced in North America one century ago. We conducted a common garden experiment, in which we measured 13 life-history traits in 4,158 field-sampled earwigs originating from 19 populations across North America. Our results first demonstrate that 10 of the 13 measured life-history traits are associated with two sets of variations in seasonal temperatures, that is, winter-summer and autumn-spring. We found, however, no association with the overall mean monthly temperatures of the invaded locations. Furthermore, our use of a common garden setup reveals that the observed patterns of variation in earwigs' life-history traits are not mere plastic responses to their current environment, but are either due to their genetic background and/or to the environmental conditions they experienced during early life development. Overall, these findings provide continent-scale support to the claims that adaptation to thermal changes can occur quickly (in less than 100 generations), even in insects with long life cycles, and emphasize the importance of variation in seasonal temperature over mean population temperatures in climate adaptation.

Changes in Energy Metabolism Trigger Pupal Diapause Transition of Bactrocera minax After 20-Hydroxyecdysone Application.

Correct timing of diapause entry and exit is critical for a species' survival. While many aspects of insect diapause are well-studied, the mechanisms underlying diapause termination remain largely unknown. The Chinese citrus fly, Bactrocera minax, is a univoltine insect with an obligatory pupal diapause. The application of 20-hydroxyecdysone (20E) is known to terminate diapause in B. minax, and we used this approach, along with isobaric tags for relative and absolute quantitation technology, to determine the proteins associated with diapause termination in this fly. Among 2,258 identified proteins, 1,169 proteins significantly differed at 1, 2, and 5 days post-injection of 20E, compared with the solvent-injected control group. Functional annotation revealed that the majority of differentially expressed proteins were enriched in the core energy metabolism of amino acids, proteins, lipids, and carbohydrates as well as in signal transduction pathways including PPAR signaling, Calcium signaling, Glucagon signaling, VEGF signaling, Ras signaling, cGMP-PKG signaling, and cAMP signaling. A combined transcriptomic and proteomic analysis suggested the involvement of energy metabolism in the response of diapause transition. RNA interference experiments disclosed that a 20E injection triggers diapause termination probably through non-genomic actions, rather than nuclear receptor mediated genomic actions. Our results provide extensive proteomic resources for insect diapause transition and offer a potential for pest control by incapacitating the regulation of diapause termination either by breaking diapause prematurely or by delaying diapause termination to render diapausing individuals at a high risk of mortality.

Multiple temperature effects on phenology and body size in wild butterflies predict a complex response to climate change.

Temperature-induced alterations in phenology and body size are the cumulative outcome of sequential effects impacting development and are universal responses to climate change. Most studies have so far focused on phenological responses to warming in multiple taxa across space and time, or the ontogenetic effects of temperature in the laboratory. I here complement this work by investigating shifts in phenology and body size (wing length) attributable to temperature changes operating over the entire lifespan of the univoltine orange-tip butterfly Anthocharis cardamines in a single wild population over 14 generations. Phenology was affected by temperatures during three discrete periods in the year prior to emergence, corresponding to late larval/early pupal life, the onset of the chilling period required to break pupal diapause, and postdiapause pupal development prior to eclosion. Higher temperatures during late larval/early pupal life and postdiapause pupal development advanced the subsequent emergence of the butterflies, whereas higher temperatures at the onset of the chilling period retarded it. The synchronization of the butterflies' emergence schedule increased when pupae were exposed to milder midwinter temperatures. Wing length increased with warmer temperatures at distinct points in the early and midpupal periods; such direct effects of temperature on body size could complement season length effects in explaining the reversal of the temperature-size rule in univoltine insects. The periods during which temperature affected the phenology of the butterfly only partially overlapped those affecting the first flowering date of its host plants lady's smock (Cardamine pratensis) and garlic mustard (Alliaria petiolata). Observed thermal effects on flowering time, emergence timing, and emergence synchronization indicate that phenological convergence as well as phenological mismatching could affect host-plant availability and diet breadth; thermal effects on body size imply that important population-level processes could be impacted through correlated changes in fecundity and dispersal rate. In general, the combined effects of phenological and ontogenetic responses to temperature changes across the whole lifespan will likely be important in modeling the demographic responses of interacting species to climate change.

How Phenological Variation Affects Species Spreading Speeds.

In this paper, we develop a phenologically explicit reaction-diffusion model to analyze the spatial spread of a univoltine insect species. Our model assumes four explicit life stages: adult, two larval, and pupa, with a fourth, implicit, egg stage modeled as a time delay between oviposition and emergence as a larva. As such, our model is broadly applicable to holometabolous insects. To account for phenology (seasonal biological timing), we introduce four time-dependent phenological functions describing adult emergence, oviposition and larval conversion, respectively. Emergence is defined as the per-capita probability of an adult emerging from the pupal stage at a particular time. Oviposition is defined as the per-capita rate of adult egg deposition at a particular time. Two functions deal with the larva stage 1 to larva stage 2, and larva stage 2 to pupa conversion as per-capita rate of conversion at a particular time. This very general formulation allows us to accommodate a wide variety of alternative insect phenologies and lifestyles. We provide the moment-generating function for the general linearized system in terms of phenological functions and model parameters. We prove that the spreading speed of the linearized system is the same as that for nonlinear system. We then find explicit solutions for the spreading speed of the insect population for the limiting cases where (1) emergence and oviposition are impulsive (i.e., take place over an extremely narrow time window), larval conversion occurs at a constant rate, and larvae are immobile, (2) emergence and oviposition are impulsive (i.e., take place over an extremely narrow time window), larval conversion occurs at a constant rate starting at a delayed time from egg hatch, and larvae are immobile, and (3) emergence, oviposition, and larval conversion are impulsive. To consider other biological scenarios, including cases with emergence and oviposition windows of finite width as well as mobile larvae, we use numerical simulations. Our results provide a framework for understanding how phenology can interact with spatial spread to facilitate (or hinder) species expansion. This is an important area of research within the context of global change, which brings both new invasive species and range shifts for native species, all the while causing perturbations to species phenology that may impact the abilities of native and invasive populations to spread.

Steep converse Bergmann's cline in a carrion beetle: between‐ and within‐population variation in body size along an elevational gradient

AbstractBody size is an integrative trait with substantial fitness consequences in animals. Geographical clines in body size have fascinated biologists because of their potential to provide insight into the mechanisms governing local adaptation and phenotypic plasticity. In this complex study, we focused on variation in body size of Silpha carinata (Coleoptera: Silphidae) along elevation gradients in Central Europe. Altitudinal clines were investigated separately for males and females as sex‐specific responses to environmental conditions are documented for a variety of insect species. To identify potential underlying mechanisms responsible for observed patterns, a common garden experiment and investigation of within‐population variation in body size were performed. Body size of S. carinata recorded in nature sharply decreased with increasing altitude in both genders, whereas sexual size dimorphism did not change with altitude. The degree of within‐population variation in body size recorded in nature did not change with altitude. Under standardized laboratory conditions, higher altitude females produced smaller eggs than those from lower altitude. This size difference persisted to the very end of the larval period. Unfortunately, only few offspring survived till adulthood in the laboratory and thus precise analysis of offspring adult sizes was unfeasible, but between‐population differences in body size seems to persist to adulthood. The observed converse Bergmann's cline in S. carinata fits well with what has been predicted for large, carnivorous, univoltine insect species. Until now, investigation of within‐population variation in body size is rare in insects, and future complementary studies focused on this issue are highly needed as within‐population variation could explain body size patterns observed at between‐population level.

Transcriptomic and metabolomic profiles of Chinese citrus fly, Bactrocera minax (Diptera: Tephritidae), along with pupal development provide insight into diapause program.

The Chinese citrus fly, Bactrocera minax (Enderlein), is a devastating citrus pest in Asia. This univoltine insect enters obligatory pupal diapause in each generation, while little is known about the course and the molecular mechanisms of diapause. In this study, the course of diapause was determined by measuring the respiratory rate throughout the pupal stage. In addition, the variation of transcriptomic and metabolomic profiles of pupae at five developmental stages (pre-, early-, middle-, late-, and post-diapause) were evaluated by next-generation sequencing technology and 1H nuclear magnetic resonance spectroscopy (NMR), respectively. A total of 4,808 genes were significantly altered in ten pairwise comparisons, representing major shifts in metabolism and signal transduction as well as endocrine system and digestive system. Gene expression profiles were validated by qRT-PCR analysis. In addition, 48 metabolites were identified and quantified by 1H NMR. Nine of which significantly contributed to the variation in the metabolomic profiles, especially proline and trehalose. Moreover, the samples collected within diapause maintenance (early-, middle-, and late-diapause) only exhibited marginal transcriptomic and metabolomic variation with each other. These findings greatly improve our understanding of B. minax diapause and lay the foundation for further pertinent studies.

How Resource Phenology Affects Consumer Population Dynamics.

Climate change drives uneven phenology shifts across taxa, and this can result in changes to the phenological match between interacting species. Shifts in the relative phenology of partner species are well documented, but few studies have addressed the effects of such changes on population dynamics. To explore this, we develop a phenologically explicit model describing consumer-resource interactions. Focusing on scenarios for univoltine insects, we show how changes in resource phenology can be reinterpreted as transformations in the year-to-year recursion relationships defining consumer population dynamics. This perspective provides a straightforward path for interpreting the long-term population consequences of phenology change. Specifically, by relating the outcome of phenological shifts to species traits governing recursion relationships (e.g., consumer fecundity or competitive scenario), we demonstrate how changes in relative phenology can force systems into different dynamical regimes, with major implications for resource management, conservation, and other areas of applied dynamics.

Predicting the resting sites of Eurygaster integriceps Put. (Hemiptera: Scutelleridae) using a geographic information system

Sunn pest Eurygaster integriceps Puton is the most destructive insect pest of wheat and barley in Iran. This pest is a univoltine insect that feeds and reproduces in the fields for only 2–3 months of the year and spends the rest of the year in resting sites. In Sunn pest management programs, the pest populations in the fields are estimated by monitoring populations in the resting sites. The objectives of this study were to find variables associated with Sunn pest resting sites, using statistical tools and a geographic information system; and predict resting sites using these variables. This study was conducted in East Azarbaijan province of Iran. Six hundred points were sampled during a three year study. The twelve topographic and environmental variables including elevation, relative elevation, slope, aspect, north–south aspect data, landshape, slope steepness, slope configuration, topographic position, soil moisture potential, sun index and normalized difference vegetation index (NDVI) were examined. The models and variables were evaluated using corrected Akaike’s information criterion (AICC). NDVI, relative elevation, elevation, topographic position, soil moisture potential, north–south aspect and aspect which had high AICC weight were used in the prediction model. The resting sites of Sunn pest in Marand County of East Azarbaijan province was predicted using the model obtained with the purpose of testing it. Comparing the predicted resting sites with the actual ones revealed that large parts of the predicted areas in south were in accordance with the actual resting sites in Marand. The generated prediction map for E. integriceps can have several applications. Targeted monitoring and management of overwintering populations of Sunn pest using this map will save time and money.

Diapause termination of Rhagoletis cerasi pupae is regulated by local adaptation and phenotypic plasticity: escape in time through bet‐hedging strategies

Persistence and thriving of univoltine, herbivore insect species of the temperate zone rely on obligate diapause response that ensures winter survival and synchronization with host phenology. We used a stenophagous fruit fly (Rhagoletis cerasi) with obligate pupae diapause to determine genetic and environmental effects on diapause intensity of geographically isolated populations with habitat heterogeneity. Pupae from two Greek and one German populations with various gene flow rates were exposed at five constant chilling temperatures (0-12°C) for different durations and then incubated at a high temperature until all adults have emerged. Pupae diapause intensity differs among Greek and German populations, suggesting an adaptive response to habitat heterogeneity (mostly differences in phenology patterns of local host cultivars). Moderately warm winter temperatures, such as 8°C, promote diapause termination in all three populations. Insufficient chilling (short duration or warmer temperatures) regulates the expression of prolonged dormancy. Interestingly, extended chilling (longer than required for terminating diapause) 'return' pupae to another (facultative) cycle of dormancy enabling adults to emerge during the next appropriate 'window of time'; a strategy first time reported for univoltine insects. Consequently, diapause duration of R.cerasi is determined both by i) the adaptive response to local climatic conditions (annual dormancy) and ii) the plastic responses to interannual climatic variability resulting in two types of long life cycles within populations, prolonged and facultative dormancy as response to insufficient chilling and extended exposure to chilling, respectively. Long life cycles are expressed as a part of dormancy bet-hedging strategies of R.cerasi populations.

Altitudinal life-cycle and body-size variation in ground beetles of the genus Carabus (subgenus Ohomopterus) in relation to the temperature conditions and prey earthworms

The body size of univoltine insect species generally decreases with increasing altitude or latitude. This pattern may have arisen from adaptations to multiple factors that potentially affect body-size variation, such as temperature, food, and interspecific interactions. We examined altitudinal variations in life history and body size, and their relationships to temperature and food resources in two ground beetle species of the genus Carabus (subgenus Ohomopterus; C. tosanus and C. japonicus) in a mountainous area (altitude 860–1730 m) of Shikoku Island, Japan. Larvae of these species are specialist predators of earthworms. The body size of C. tosanus decreased with an increase in altitude. Carabus japonicus, which is much smaller than C. tosanus, exhibited similar sizes across altitudes, although it was not abundant at high altitudes. Available cumulative temperatures for larval development were limited at higher altitudes, and C. tosanus started reproducing 1 month earlier at higher than at lower altitudes. Earthworms (larval food) were less abundant at higher than at lower altitudes. This may imply that food resources also restrict the optimal body size of C. tosanus at higher altitudes.

ASSORTATIVE MATING COUNTERACTS THE EVOLUTION OF DISPERSAL POLYMORPHISMS

Polymorphic dispersal strategies are found in many plant and animal species. An important question is how the genetic variation underlying such polymorphisms is maintained. Numerous mechanisms have been discussed, including kin competition or frequency-dependent selection. In the context of sympatric speciation events, genetic and phenotypic variation is often assumed to be preserved by assortative mating. Thus, recently, this has been advocated as a possible mechanism leading to the evolution of dispersal polymorphisms. Here, we examine the role of assortative mating for the evolution of trade-off-driven dispersal polymorphisms by modeling univoltine insect species in a metapopulation. We show that assortative mating does not favor the evolution of polymorphisms. On the contrary, assortative mating favors the evolution of an intermediate dispersal type and a uni-modal distribution of traits within populations. As an alternative, mechanism dominance may explain the occurrence of two discrete morphs.

Physiological and biological patterns of a highland and a coastal population of the European cherry fruit fly during diapause

Adult emergence of univoltine temperate insect species and its synchronization with specific host phenological stages is mainly regulated by obligatory pupal diapause. Although a few studies have investigated the factors affecting diapause intensity, little attention has been paid to the physiological alterations and metabolic regulation that take place during diapause. Here, we describe differences in diapause between a highland and a coastal Greek population of the European cherry fruit fly Rhagoletis cerasi, a major pest of sweet and sour cherries in many European countries. Pupae of both populations were exposed to the environmental conditions prevailing in the two areas and diapause termination was observed under laboratory conditions. The regulation of energetic metabolites during the long pupae stage was examined under both field and laboratory conditions. Differences in diapause intensity revealed that the two populations have adapted to the local geographical and climatic conditions and have different requirements for low temperatures to terminate diapause. The coastal population undergoes a shorter diapause and adults emerge more rapidly, especially in the highland area. The highland population failed to terminate diapause (<40% adult emergence) in the coastal area. Both populations draw on their major energetic reserves (lipids and protein) similarly during diapause. Nevertheless, regulation of carbohydrate and glycogen reserves seems to vary between the populations: major peaks of these stored nutrients occur on different dates in the two populations, suggesting a differential regulation. Differences in diapause intensity imply a genetic differentiation between the two populations. The importance of our findings in understanding the physiological patterns during obligatory diapause of a univoltine insect species, as well as the practical implications for the development of specific phenological models for the European cherry fruit fly are discussed.

Transfer of life-history phenology from mothers to progeny in a solitary univoltine parasitoid

Among univoltine insects that experience diapause, differences in emergence timing between adult males and females are expected to be dictated by sex-specific developmental factors. In multivoltine insects without a diapause, there is often an additional relationship between the date of oviposition and the date of adult emergence. Differences between male and female emergence timing in the latter case can therefore be influenced by female sex-allocation decisions. In the present study, it is shown that eggs of a univoltine parasitoid wasp Diachasma alloeum Muesebeck (Hymenoptera: Braconidae) that are laid earlier also eclose earlier during the subsequent year, independent of (although complementary to) sex-related differences in development time. The implications of this pattern for sex allocation decisions by female univoltine parasitoids are discussed.

Correlation of oxygen consumption, cytochrome c oxidase, and cytochrome c oxidase subunit I gene expression in the termination of larval diapause in the bamboo borer, Omphisa fuscidentalis

The moth Omphisa fuscidentalis (Lepidoptera, Pyralidae) is a univoltine insect with a larval diapause period lasting up to 9 months. We studied changes in O 2 consumption in conjunction with cytochrome c oxidase activity and cytochrome c oxidase subunit I ( cox1) gene expression. O 2 consumption changed within a day, showing a supradian rhythm with a ca.12-h cycle at 25 °C. During the first two-thirds of the diapause period, from October to March, O 2 consumption was constant until January and then increased by March. Topical application of methoprene, a juvenile hormone analog (JHA), to diapausing larvae terminated the diapause and was associated with an increase in O 2 consumption rate at diapause termination. In JHA-treated larvae, cytochrome c oxidase activity in fat bodies was high at the beginning of the prepupal period and highest at pupation. cox1 expression in fat bodies displayed a transient peak 8 days after JHA application and peaked in the prepupal period. Taken together, our results show that the break of diapause by JHA is associated with the activation of cox1, bringing about an increase in cytochrome c oxidase activity, followed by an increase in O 2 consumption rate.

ARE REPRODUCTIVE TACTICS DETERMINED BY LOCAL ECOLOGY IN ROMALEA MICROPTERA (ORTHOPTERA: ACRIDIDAE)?

We tested whether reproductive tactics of a univoltine insect can be predicted by local ecology, specifically mean length of the frost free period (FFP) as a measure of the potential active season. We measured reproductive tactics and longevity for populations of the lubber grasshopper Romalea microptera (Beauvois) from Miami, Florida (FL; 365 days FFP), Lydia, Louisiana (LA; 280 days FFP), and Athens, Georgia (GA; 224 days FFP). Differences in local climate led us to predict that GA grasshoppers will have shorter interclutch intervals, fewer clutches, and shorter lifespan than FL grasshoppers, with LA grasshoppers intermediate in these traits. When reared in a common laboratory environment, longevity, total reproductive period, and number of clutches produced were not clearly related to FFP. Longevity and reproductive period of LA grasshoppers were significantly less than those of FL grasshoppers, and number of clutches produced by LA grasshoppers was less than that for the FL or GA grasshoppers. First interclutch interval was significantly greater for LA than for GA grasshoppers. Our data suggest that phylogenetic relationships among populations may be a better predictor of reproductive tactics in this species.

Recent history of Moroccan locust control and implementation of mechanical control methods in northern Afghanistan

Moroccan locust, Dociostaurus maroccanus (Orthoptera: Acrididae), is a univoltine insect and an annual pest of wheat, the staple crop in northern Afghanistan. By 1996, the funds that had supported emergency locust control programmes, based on ultra low volume (ulv) technology (a combination of specific application machinery and insecticide formulation that allows volume application rates of typically around one litre insecticide/ha for locust control work) and implemented by the United Nations since 1990, became exhausted. Donors were reluctant to support further purchases of insecticides for a country in the grip of a civil war. Consequently, mechanical control, used by generations of Afghan farmers to protect their crops, was reintroduced. Mechanical control, which involves the monitoring of egg beds in the spring to predict egg hatch, together with the timely mobilization of communities to dig trenches in front of the advancing bands of hoppers, does not use insecticides. Between 1996 and 1999, about 30 000 ha of locusts were cleared by mechanical control saving the purchase of insecticide worth around US$300 000. Mechanical control worked best when the locust was not in an outbreak phase, when the authorities supported the mobilization of communities and when labour was not in short supply. Where circumstances allow, the timely implementation of mechanical control of Moroccan locust is proposed as a means to protect crops and as a strategy to preserve scarce resources.