Potential rates of Increase of solitarious and gregarious phases of the African armyworm Spodoptera exempta (Lepidoptera: Noctuidae)

Abstract.

• 1 The African armyworm Spodoptera exempta exhibits a phase polyphenism with insects capable of transforming from one‘phase’to another, which involves both physiological and behavioural changes. Amongst these changes, evidence from the laboratory and the field suggest that, given equivalent conditions of temperature and food, solitary phase insects take longer to complete their life cycles than gregarious phase insects, and the latter's generations are more synchronized. There is also some evidence that females of the solitary form sometimes lay more eggs.
• 2 Using data from field and laboratory studies, estimates of the rates of increase of each form were calculated from Leslie matrix models. Assuming equivalent mortality rates for both phases, asynchronous development for the solitaries and synchronous development for the gregarious forms, with the latter having lower fecundities than the solitaries, the models suggest that the gregarious forms have higher values of their intrinsic rates of increase (r) than solitarious populations. These results are explored using a range of parameter values including variation in the percentage of solitaries with delayed development.
• 3 The possible ecological and evolutionary significance of variations in rates of increase of gregarious and solitary populations are briefly discussed.

     

A correlation between macronutrient balancing and insect host-plant range: evidence from the specialist caterpillar Spodoptera exempta (Walker)

In an earlier study, we showed that the ingestive responses of the generalist caterpillar Spodoptera littoralis to foods imbalanced in their protein:carbohydrate content is similar to generalist locusts, but differs from that of specialist-feeding locusts. Here we further pursued the comparison by repeating the experiments using a closely related specialist caterpillar, Spodoptera exempta. First, caterpillars were allowed to self-compose a diet of preferred protein:carbohydrate balance by mixing between nutritionally complementary foods. Then, they were confined to one of five imbalanced foods, in which we measured the trade-off between over- and under-ingesting the two nutrients. On complementary foods, the caterpillars actively regulated their protein and carbohydrate intake. In the no-choice experiment, those fed excess-protein foods ingested small surpluses of protein compared with generalist feeders, thus showing a pattern of nutrient balancing similar to that observed in specialist locusts. Utilisation data indicated that ingested excesses and deficits were to some extent offset by differential utilisation. Evidence also showed that post-ingestive responses of the specialist S. exempta were less flexible than those observed in the generalist S. littoralis, a pattern which is again in accordance with comparisons of acridids differing in their host-plant range.     

Sex-specific differences in nutrient regulation in a capital breeding caterpillar, Spodoptera litura (Fabricius)

Nutrient requirements by male and female insects are likely to differ, but relatively little is known regarding how sexes differ in their regulation of macronutrient acquisition. The present study reports the results from a laboratory experiment in which behavioural and physiological components of nutrient regulation were compared between male and female caterpillars of Spodoptera litura (Fabricius). When provided with choices between two nutritionally complementary foods (one is a protein-biased diet and the other a carbohydrate-biased diet), both males and females adjusted their food selection to defend an intake target. However, the composition of diet preferred by the two differed, with females selecting significantly more protein than males with no difference in carbohydrate intake between the two. When confined to single diets with varying mixtures of protein and carbohydrate [P:C ratios, expressed as the percentage of diet by dry mass: protein 42%:carbohydrate 0% (p42:c0), p35:c7, p28:c14, p21:c21, p14:c28, p7:c35], females consumed more macronutrients than did males across on all P:C diets except the extremely carbohydrate-biased diet (p7:c35). Under both choice and no-choice feeding condition, such sex differences in nutrient intake were not expressed until late in the feeding stage of the final stadium. Sexes also differed in post-ingestive utilization of ingested nutrients. Females utilized ingested protein for body growth with greater efficiency compared to males, presumably reflecting provisioning their adult needs for protein to develop eggs, whereas males were more efficient at depositing lipids from carbohydrate intake than females.     

Trade-off between flight and reproduction in the African armyworm moth, Spodoptera exempta

ABSTRACT. The existence of a trade-off between flight and reproduction in the migratory noctuid, Spodoptera exempta (Wlk.), was examined in experiments in which female moths were flown on flight balances and then provided with distilled water or sucrose solution. For individuals flight-tested from the night of eclosion (night 0) through night 1 and fed only distilled water, there was a linear, negative relationship between weight-related fecundity and flight duration. When flight was recorded through night 2, a curvilinear relationship was obtained suggesting that highly active moths suffer a smaller decrease in fecundity than predicted from its rate of decline with increasing flight duration in less persistent fliers. The hypothesis that this reflects an energetically expensive, initial phase of each flight, followed by a less costly, cruising phase is examined. Fecundity was independent of flight duration in females provided with sucrose after flight but was related to moth weight, as it was in all unflown moths. Effects of flight and feeding on longevity and mating frequency are also reported.
There is a clear trade-off between flight and fecundity in S.exempta which is only evident in moths denied access to a source of carbohydrate after flight. The results indicate the importance of nectar sources in the field in allowing restoration of lipid reserves depleted during migratory flight. An important implication of this conclusion is that lipid is the resource limiting to fecundity in this species and not protein as is generally supposed for leaf-feeding insects. This might be expected in highly active species as lipid is the resource for which the energetically expensive functions of flight and reproduction must compete.     

Effects of the availability of food and water on reproduction in the African army worm, Spodoptera exempta

ABSTRACT. Female Spodoptera exempta (Walker) (Lepidoptera: Noctuidae) moths require access to water to achieve hydration and maturation of their oocytes if they are to achieve their potential fecundity. For moths provided with water, the main factor limiting fecundity is moth weight. There is some evidence that sucrose in the adult diet can increase fecundity, particularly in lighter moths from a suboptimal larval feeding regime. Moths fed sucrose live longer, but complete oviposition at about the same age as moths provided only with water. Dietary protein and amino acids have no effect on fecundity or longevity. Although- multiple matings are frequent in the laboratory, female S.exempta only need to mate once to complete oviposition. Differences are apparent in the relative contribution of larval and adult feeding to reproduction in Noctuidae. Some species, like S.exempta , require only water to achieve their reproductive potential, while others (e.g. Heliothis spp.) are dependent on sugars in the adult diet. Female S.exempta denied access to water or food until night 3 after eclosion and then provided with water or sucrose, commence oviposition on night 4 and have fecundities comparable with those moths fed from emergence.     

Downwind migration of the African army worm moth, Spodoptera exempta, studied by mark-and-capture and by radar

Abstract. 1. About 166,000 African armyworm moths, Spodoptera exempta (Walk.), were marked at an emergence site near Nairobi when they fed at night on trees baited with dyed molasses.
2. Six marked moths were captured in pheromone traps, including one at 90 km after flying for only one night, and another at 147 km.
3. Moth flight trajectories deduced from radar and from marking showed that migration was downwind.
4. During migration, moths become dispersed; hence the high densities that lead to outbreaks must be produced by concentration.
5. Some moths were ready to mate on the same night they completed their long-distance flight.     

The determination of larval phase coloration in the African armyworm, Spodoptera exempta and its consequences for thermoregulation and protection from UV light

Spodoptera exempta exhibits a density-dependent phase polyphenism in which caterpillars reared in isolation (phase solitaria) tend to be green/brown and cryptic while those reared in groups (phase gregaria) are black and highly visible. Differences in coloration between solitaria and gregaria phase larvae become apparent in the third instar and are pronounced by the final instar. Larval rearing densities as low as two larvae per 250 ml container are sufficient to induce gregaria coloration in 61% of the insects and at higher densities this is the only coloration expressed. Larvae transferred from isolated to crowded conditions or vice versa tend to retain or adopt gregaria phase coloration which suggests that this is highly advantageous. Black coloration is also induced in single larvae reared with other species of caterpillar (S. littoralis). Isolated larvae reared at low temperature tend to become melanic while crowded larvae reared at high temperature tend to be less melanised although they do not adopt the solitaria phase coloration. These results suggest that phase coloration is determined by non species-specific inter-larval contact, although it can be modulated by temperature. Under laboratory conditions, gregaria phase larvae heat up faster than solitaria; this is partially a consequence of their black coloration but their smaller size is a more important factor. The cuticles of the gregaria larvae absorb significantly more ultraviolet radiation than those of solitaria but this does not confer any protection when larvae are irradiated at 254 nm.     

Observations of the flight behaviour of the army worm moth, Spodoptera exempta, at an emergence site using radar and infra-red optical techniques

ABSTRACT.

• 1 Studies were made in Kenya of the flight behaviour of African armyworm moths which had emerged from areas previously infested with‘gregarious’caterpillars. The use of radar and an infra-red optical detector permitted quantitative, direct observations of the flying moths, over all of their flight altitudes, without disturbing their behaviour.
• 2 Almost all of the successfully emergent moths climbed to altitudes of several hundred metres above ground level and migrated from the emergence sites. Their migratory flights sometimes started on the night of emergence, but on other occasions the moths remained roosting in trees until dawn, then engaged in short dispersal flights, concealed themselves during the day. and commenced migration in mass flights at dusk the following night.
• 3 The onset of these‘dusk flights’occurred when the irradiance level fell on average to 2.7 × 10^?5Wm^?2 nm^?1 in the 450–800 nm range (in the photometric units appropriate for human vision this corresponds approximately to 2 lux). The‘dawn flights’began with the first sustained increase in irradiance at dawn, and terminated at the end of dawn twilight.
• 4 Migratory flight in the strong, easterly winds which usually occurred during the first half of the night resulted in rapid, down-wind displacement to the west. Observations of groups of flying moths passing successively over two radars demonstrated that these migrations could cover at least 20 km.
• 5 In the second half of the night, winds were usually weak and variable, and up-wind or cross-wind directions of displacement were sometimes observed.
• 6 Moths were observed to disperse rapidly during their migration, so that the mass influxes which lead to outbreaks must be a consequence of subsequent reconcentration. The importance of meso-scale wind convergence zones in reconcentrating flying moths, and the role of rainfall in inducing descent, and possibly landing, are discussed.

     

A geometric analysis of nutrient regulation in the generalist caterpillar Spodoptera littoralis (Boisduval)

Nutritional regulatory responses of the generalist caterpillar Spodoptera littoralis (Boisduval) were explored, in choice and no-choice experiments, using the Geometric Framework. In the choice experiment, newly moulted final instar larvae were provided with one of three protein-biased foods (PB-food: p35:c7, p28:c5.6 or p21:c4.2) and one of three equal protein-carbohydrate ratio foods (ER-food: p21:c21, p16.8:c16.8 or p12.6:c12.6). On five of the nine treatments, caterpillars independently regulated protein and carbohydrate intake to a mixture of 57 and 43%, respectively. However, when the concentration of the ER-food decreased and that of the paired PB-food increased, caterpillars progressively abandoned regulation and ate more of the PB-food. Despite these regulatory differences, performance (survivorship, growth and development) was similar across all nine treatments. In the no-choice experiment, caterpillars were given one of five foods (p35:c7, p28:c14, p21:c21, p14:c28 and p7:c35). Results indicated that caterpillars moved to a point in protein-carbohydrate space that was consistent with the Equal Distance Rule of compromise, a pattern previously predicted for generalist feeders. The insects on the two extreme foods, p35:c7 and p7:c35, showed reduced pupal mass and longer development, respectively. There was also strong evidence for post-ingestive regulation of nutrient utilisation, notably for protein.     

Localization of visual pigments within rhabdoms of the compound eye of Spodoptera exempta (Insecta,Noctuidae)

Summary In the noctuid moth Spodoptera exempta, the distribution of visual pigments within the fused rhabdoms of the compound eyes was investigated by electron microscopy. Each ommatidium regularly contains eight receptor cells belonging to three morphological types: one distal, six medial, and one basal cell (Meinecke 1981); four different visual pigments — absorption maxima at approximately 355, 465, 515, and 560 nm — are known to occur within the eye (Langer et al. 1979). The compound eyes were illuminated in situ by use of monochromatic light of different wavelengths. This illumination produced a wide scale of structural changes in the microvilli of the rhabdomeres of individual cells. Preparation of eyes by freeze-substitution revealed the structural changes in the rhabdomeres to be effects of light occurring in vivo.The degree of structural changes may be considerably different in rhabdomeres within the same ommatidium; it was found to depend on the wavelength and the duration of illumination, the intensity received by the ommatidia as well as the spectral sensitivity of the receptor cells. Therefore, it was possible to estimate the spectral sensitivities of the morphological types of receptor cells. Generally, all medial cells are green receptors and all basal cells red receptors; distal cells are blue receptors in about two-thirds of the ommatidia, while in the remaining third of them distal cells are sensitive to ultraviolet light.Supported by Deutsche Forschungsgemeinschaft, Sonderforschungsbereich 114 (Bionach)     

Simultaneous monitoring of flight and oviposition of individual velvetbean caterpillar moths (by Wales, Barfield & Leppla, 1985): a critique

ABSTRACT. Flight durations of tethered female Anticarsia gemmatalis moths recorded in the laboratory were interpreted by Wales et al. as indicating a capacity for significant inter-reproductive displacements in the field. Indications that their data may not support this conclusion are discussed and evidence is presented that, in tethered Spodoptera exempta , prolonged flights starting early in the night represent migratory behaviour while those of similar durations starting after midnight do not.     

Feeding deterrence,larvicidal and haemolymph protein profiles of an Indian traditional medicinal plant Alangium salviifolium (L.F.) Wangerin on cluster caterpillar,Spodoptera litura (Fabricius) (Lepidoptera: Noctuidae)

Different organic solvent crude extracts from the leaves of Alangium salviifolium (L.F.) Wangerin, were tested for their feeding deterrence, larvicidal activity and protein concentrations on the fourth instar larvae of Spodoptera litura L. under laboratory conditions. Treatments were given through two different host plant leaves such as brinjal and castor. The bioassay was carried out at different concentrations viz., 0.625, 1.25, 2.5 and 5%. The maximum antifeedant activity in brinjal (52.0%) and castor (29.97%) leaf discs was recorded in ethyl acetate extract as compared with hexane and chloroform extracts at 5% concentration. The result of larvicidal activity revealed that the maximum larval mortality was registered in brinjal leaves (65.81%) and castor with (57.48%) in ethyl acetate extract as compared to hexane and chloroform extracts at 5% concentration. The ethyl acetate extract of A. salviifolium contained alkaloids, diterpenoids, and saponins. The treatment also reduced haemolymph protein concentration after 48 h.     

Interaction between MbMNPV and the braconid parasitoid Habrobracon hebetor (Hym., Braconidae) on larvae of beet armyworm,Spodoptera exigua (Lep., Noctuidae)

The survival of a braconid parasitoid Habrobracon hebetor was investigated on nucleopolyhedrovirus (NPV)-infected Spodoptera exigua larvae. The second-instar larvae were exposed to 30, 51.4 and 180 PIB/mm² of Mamestra brassicae NPV (MbMNPV) as under-LD₅₀, LD₅₀ and over-LD₅₀ values, respectively. They were accessible to be parasitized by H. hebetor after 24, 48 and 72 h post-treatment. Infection of the larvae with MbNPV was deleterious to the survival and parasitism of H. hebetor. The survival of H. hebetor in MbNPV-infected S. exigua larvae was dependent on the interval between viral infection and parasitization, as well as on the treatment dose of MbMNPV; very few adults of parasitoid emerged from infected hosts when host larvae were exposed to 180 PIB/mm² of MbNPV on 72-h interval treatment. The inoculation dose of MbNPV and the timing of parasitoid release had significant effect on the development of H. hebetor on virus-infected hosts. Field applications of virus for biocontrol of S. exigua may lead to substantial mortality of immature parasitoids.     

小叶黑面神与小叶头细蛾互惠共生系统的种群调控机制(英文)

【目的】探索小叶黑面神Breynia vitis-idaea对小叶头细蛾Epicephala vitisidaea种群数量的调控机制。【方法】跟踪记录小叶黑面神物候及头细蛾的生物学。解剖在小叶黑面神上访花头细蛾的外生殖器,鉴定头细蛾种类。对不同时期小叶黑面神有梗和无梗的果实进行解剖,统计果实内幼虫数量、果实表面孔的数量以及果实表面产卵疤数量,计算头细蛾幼虫存活率。统计不同时期小叶黑面神有梗和无梗的果实的比例。【结果】在福建厦门小叶黑面神每年有5个花果期,相应地,为小叶黑面神传粉的头细蛾每年有5个生活世代。通过解剖,该种头细蛾被鉴定为小叶头细蛾。一头小叶头细蛾幼虫需要消耗2~4粒种子才能发育成熟。小叶黑面神有两种不同形态的果实:有梗和无梗。头细蛾幼虫在无梗果实内的存活率明显高于有梗果实,并且晚秋时期头细蛾幼虫的存活率要高于夏季。小叶黑面神无梗果实的比例在晚秋(82.04%)要高于夏季(31.53%)。【结论】本研究揭示了维持互利共生体系稳定的机制。小叶黑面神能够通过果实基部果梗的有无来调节小叶头细蛾幼虫的存活率。小叶黑面神通过季节性的调节有梗果实的比率,既有效避免了夏季种子被过度消耗的风险,又提高了头细蛾在冬季的存活率。小叶黑面神这种自身调控机制对维持小叶黑面神与小叶头细蛾互惠共生系统的稳定性起到了至关重要的作用。     

Effects of an optical brightener on the development, body weight and sex ratio of Spodoptera frugiperda (Lepidoptera: Noctuidae)

The incorporation of stilbene-derived optical brighteners into baculovirus formulations can substantially enhance virus infectivity and persistence of inoculum in the field. We evaluated the effect of the optical brightener Tinopal UNPA-GX (Sigma Chemical Co.) on the weight, development time, adult emergence and sex ratio of the principal pest of maize in the Americas, Spodoptera frugiperda (J. E. Smith) (Lepidoptera: Noctuidae). Tinopal UNPA-GX was incorporated into semi-synthetic diet at a final concentration of 0.1 or 0.05% (w/v) and larvae of S. frugiperda were individually reared on the Tinopal-treated or an untreated control diet. In both Tinopal treatments, the weights of larvae and pupae were significantly reduced by up to 36 and 13%, respectively. The duration of larval development was increased by up to 30% compared to the controls. Adult emergence was high in all treatments (≈90%) and was not affected by the presence of Tinopal in the diet. Significant differences in the proportion of adult females were observed in the 0.05% Tinopal treatment but not in the control or 0.1% Tinopal treatments. By affecting the integrity of the peritrophic membrane and the rate of sloughing of intestinal epithelial cells, natural pest populations exposed to optical brightener residues from bioinsecticide applications are likely to suffer a reduction in growth rate and other correlates of insect fitness.     

Expression of the cry1EC gene in castor (Ricinus communis L.) confers field resistance to tobacco caterpillar (Spodoptera litura Fabr) and castor semilooper (Achoea janata L.)

Castor (cv. DCS-9) has been transformed through Agrobacterium-mediated and particle gun bombardment methods using appropriate vectors containing the Bt chimeric gene cry1EC driven by enhanced 35S promoter. About 81 and 12 putative transformants were regenerated following selection on hygromycin and kanamycin, respectively. Southern analysis of DNA extracted from T₀ plants confirmed integration of the introduced gene in castor genome. The integration and inheritance of the introduced genes was demonstrated up to T₄ generation by PCR and Southern analysis. Southern analysis of two events having single and two copies showed the same pattern of integration in the subsequent generations. Insect feeding experiments conducted in the laboratory by releasing neonate larvae of castor semilooper and S. litura on leaf tissues excised from transgenic and control plants showed varying degrees of larval mortality and slow growth in larvae fed on transgenic leaf tissue. Field bioassays against Spodoptera litura and castor semilooper conducted for eight events in T₁–T₄ generations under net confinement were more informative and events conferring resistance to the two major defoliators were identified.     

Growth and survival performance of the gametophyte of Gigartina skottsbergii (Rhodophyta, Gigartinales) under defined nutrient conditions in laboratory culture

Gigartina skottsbergii is a commercially important carrageenan producer that has been suffering severe extraction pressure in Chile’s Magellan Region and Cape Horn Archipelago since 1998. In order to create baseline information for its cultivation and repopulation, we studied the effects of agricultural fertilizers on growth of G. skottsbergii early developmental stages. The culture media utilized were: a) seawater + Bayfoland, b) seawater + Superphosphate, c) seawater + Urea, d) seawater + Provasoli and e) seawater as a control. The culture conditions were: a) 12L:12D photoperiod; b) temperature 8 ± 1°C and c) irradiance at 45 μmol photons m⁻² s⁻¹. After 60 days, higher relative growth rates between treatments were observed; the treatments that included Bayfoland and Provasoli showed greater growth (382 ± 55 and 378 ± 50 μm, respectively,) compared to Superphosphate (88 ± 16 μm), control (78 ± 10 μm) and Urea (70 ± 11 μm) treatments, after 81 days. The Urea treatment and the control had inhibitory effects on G. skottsbergii germlings growth and survival, as evidenced by progressive loss of pigmentation and death after 60 days. These results showed that Bayfoland was an excellent alternative to develop cultures.     

Bone mineral density and genetic markers involved in three connected pathways (focal adhesion,actin cytoskeleton regulation and cell cycle): the CUMAGAS-BMD information system

The focal adhesion, the actin cytoskeleton and cell-cycle are connected pathways and their genes are implicated in the pathogenesis of low BMD. Data from 211 studies that investigated the association between BMD and gene variants involved in these pathways were catalogued in a web-based information system and analyzed. In individual studies, significant association was found for 16 variants in lumbar spine, 11 in femoral neck and 5 in hip. In meta-analysis, significant results were shown for the variants COL1A1 rs1800012 (in lumbar spine and femoral neck), COL1A1 rs1107946 (in lumbar spine), TGFB1 rs1982073 (in femoral neck and hip) and TGFB1 rs1800469 (in lumbar spine).     

A comparison of startle response in two morphs of the brook stickleback (Culaea inconstans): Further evidence for a trade-off between defensive morphology and swimming ability

It is generally thought that predation pressure drives the evolution of long spines and robust pelvic girdles in sticklebacks (Pisces: Gasterosteidae). However, the lack of these traits in some environments with intense predation pressure suggests that there may be a limit to which apparently defensive structures benefit sticklebacks. This paper focuses on a trade-off between defensive morphology and escape response performance in a genetically based polymorphic population of brook stickleback (Culaea inconstans), in which fish have fully developed pelvic girdles and pelvic spines (complete morph) or completely lack these defensive structures (absent morph). Startle response experiments revealed that the absent morph did better in all aspects of startle performance (displacement, maximum velocity, acceleration) than the complete morph. The absent morph also bent deeper than the complete morph during the initial phase of the startle response. The pelvic girdle polymorphism in this population may be maintained because individuals with a complete pelvic girdle and spines may be able to escape more easily from predators once they are captured, whereas individuals lacking these structures may better avoid capture when they are attacked.