The effect of adult feeding on lipid and protein reserves in African armyworm, Spodoptera exempta, moths before and during reproduction

ABSTRACT. Newly-emerged Spodoptera exempta (Walker) (Lepidoptera: Noctuidae) moths contain high levels of lipid held largely in the abdominal fat body, the quantity depending on the larval feeding conditions. There is a positive relationship between weight-related lipid content and moth weight, which is consistent for female but not for male moths, suggesting that larval feeding conditions producing large individuals allow the accumulation of quantitatively disproportionate lipid reserves. Male and female moths have comparable levels of abdominal protein.
Changes in the water content in starved moths or ones provided with distilled water or sucrose solution show that while starved individuals die rapidly from desiccation, water-fed moths regulate their water contents between narrow limits which are higher for females than for males. Sucrose-fed moths maintain higher, more variable water contents probably due to the phagostimulatory effect of the sugar.
Reproducing and unmated moths are able to supplement their lipid and, to a lesser extent, their protein reserves following carbohydrate uptake.
During both larval and early adult stages, the capacity to accumulate lipid reserves in excess of those apparently required for reproduction, suggests that these reserves also provide the main fuel for the prolonged flights of which migratory individuals are known to be capable.     

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.     

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.     

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.

     

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.     

A comparison of nutrient regulation between solitarious and gregarious phases of the specialist caterpillar, Spodoptera exempta (Walker)

Nutritional regulatory responses were compared between solitarious and gregarious phases of the African armyworm, Spodoptera exempta. When allowed to mix between two nutritionally imbalanced but complementary foods, final-instar caterpillars in both phases selected a diet comprising more carbohydrate than protein. This contrasts with other larval lepidopterans studied to date. Only minor differences were found in the position of the intake target for the two phases, despite their different energetic requirements for migration as adults. When restricted to nutritionally imbalanced diets, caterpillars of both phases were less disposed to overeat protein on high-protein diets than carbohydrate on high-carbohydrate diets, relative to the self-composed intake target. However, in both cases gregarious larvae overingested the excess nutrient to a greater degree than did solitarious larvae. Furthermore, gregarious larvae showed higher nitrogen conversion efficiency on an extreme protein-limiting diet, and accumulated more lipid per amount of carbohydrate consumed on carbohydrate-deficient diets. These phase-associated nutritional differences are consistent with the life-history strategies of the two phases.     

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.

     

Fitness consequences of cannibalism in the fall armyworm, Spodoptera frugiperda

We investigated the consequences of cannibalism for some correlatesof fitness in the fall armyworm, Spodoptera frugiperda (Lepidoptera: Noctuidae).The benefits gained by cannibals were ascertained by comparing survival,development rate, and pupal weight of larvae that had the opportunityto cannibalize with those that did not, at two levels of food availability.Larvae in the cannibalism treatments were provided with a conspecificone instar younger than themselves on five dates throughoutlarval development. Cannibalism was frequent; given the opportunityall larvae predated at least one younger conspecific. The frequencyof cannibalism was not affected by the sex of the cannibal orby the availability of alternative food. However, cannibalssuffered a significant reduction in survival at both high andlow food availability. Furthermore, cannibals had a lower pupal weightin the high food treatment and a reduced development rate inthe low food treatment. The only detectable fitness benefitassociated with cannibalism was a positive correlation betweenthe number of victims consumed and development rate under conditionsof low food availability. On balance, cannibalism appears tobe costly; alternative explanations for its occurrence in thisspecies are discussed.     

Increase in respiratory rate during feeding in larvae of the armyworm, Spodoptera exempta

Oxygen consumption was measured in fifth and sixth instar larvae of Spodoptera exempta (Walker) (Lepidoptera, Noctuidae) at 25d?C using Warburg manometry. The mean rate of oxygen consumption while feeding on maize or sorghum leaves was approximately twice that at rest. The increment in oxygen consumption attributable to feeding was 583±207 μlg-¹ h-^l (mean±95% confidence limits) or, for maize, 6.1±3.5 μl O₂ per mg of leaf eaten.     

Effects of Azadirachtin on reproduction in the African armyworm (Spodoptera exempta)

Azadirachtin, applied topically to final instar larvae of the African armyworm (Spodoptera exempta, Walker) (Lepidoptera: Noctuidae), adversely affected oogenesis and reproductive maturation in subsequent female moths. Moths obtained from such treated larvae failed to mature their oocytes, probably as a result of interference of azadirachtin with vitellogenin synthesis and/or its uptake by developing oocytes. Such larval treatment also caused substantial decreases in fecundity and although fertility in affected females was not decreased significantly, emerging larvae were less viable, less than 40% reaching the fourth instar.Closer examination revealed that protein levels as well as fat body development in female moths were suppressed by azadirachtin. Prospects for field control of this pest with neem are discussed in the light of these findings.

---

Résumé L'application locale d'azadirachtine sur des chenilles de dernier stade de S. exempta Walker nuit à l'ovogenèse et à la maturation des ovaires des futures femelles. Les papillons provenant des chenilles traitées ne produisent pas d'ovocytes mûrs, probablement par suite de l'interférence de l'azadirachtine avec la synthèse de la vitellogénine et/ou son incorporation dans les ovocytes en développement. De tels traitements larvaires provoquent aussi une diminution importante de la fécondité et bien que la fertilité des femelles touchées ne diminue pas significativement, les chenilles néonates sont moins viables, moins de 40% atteignant le 4^e stade. Un examen plus précis a révélé que la teneur en protéines et le développement du corps gras des papillons femelles étaient altérés par l'azadirachtine. Des perspectives d'utilisation du NEEM dans la lutte contre cet insecte ont été discutées à la lumière de ces résultats.

     

甜菜夜蛾抗药性研究现状

就有关甜菜夜蛾Spodoptera exigua(Hbner)对常用杀虫剂的抗药性现状作综述。甜菜夜蛾对拟除虫菊酯类、有机磷类、氨基甲酸酯类杀虫剂已产生了较高水平的抗药性,其中山东泰安抗性种群对氯氟氰菊酯的抗性高达2445.5倍;对多杀菌素等生物杀虫剂产生了中低水平的抗性;对昆虫生长调节剂如虫酰肼的敏感性也有所降低,但昆虫生长调节剂依然是比较理想的防治药剂。对交互抗性及抗性治理也作了阐述。     

The migration syndrome in the African armyworm moth, Spodoptera exempts: allocation of resources to flight and reproduction

Abstract. Selection for the capacity for prolonged tethered flight in Spodoptera exempta resulted in heavier moths, with significantly larger abdominal glyceride glycerol contents in females of two flight-selected strains (87% and 49% higher than in the comparable non-selected strain) and in males of one of them (80% higher). All flight-selected strains contained individuals of both sexes with very high abdominal glyceride levels. There was no significant relationship between abdominal total glyceride glycerol after flight and flight duration for non-selected moths, but an inverse linear relationship was evident in both sexes from a flight-selected strain. Oxygen consumption during tethered flights by flight-selected moths ranged from 28.2 to 56.6 ml O₂g^-1h^-1.
Using these and previous data, notional energy budgets were calculated to account for flight, reproduction and resting metabolism for non-selected and flight-selected S. exempta flown on the flight balances and provided thereafter with distilled water. The results confirm the trade-off between flight and reproduction reported by Gunn et al. (1989). A similar approach using data for two non-selected strains from the field in Kenya indicated genetic variation in migratory potential, reflected both in pre-reproductive period and resources available for flight. We conclude that elevated glyceride levels are a component of the migratory syndrome in S. exempta and that this is the major factor underlying the curvilinear relationship between flight duration and fecundity obtained by Gunn et al. (1989).     

The chronology of the cercopithecoidea of East Africa

The East African fossil record of cercopithecoids spans nearly 20 m. y. Throughout the Miocene Epoch, the diversity of monkeys was low, although at some localities the numbers of individuals is rather high. During the Plio-Pleistocene in contrast, there was a major radiation, or radiations of monkeys, involving both colobines and corcopithecines. A late Pleistocene to Recent radiation within the genusCercopithecus still seems to be under way. The history of diversity in the monkeys is in many ways a chronological inverted mirror image of the diversity history of the hominoid primates, which were highly diverse during the lower miocene, but became less diverse through time. The east african cercopithecoid record is the only one which spans much of the Neogene, and it is consequently the main one by which detailed cercopithecoid cladogenetic and anagenetic events can be dated. In this respect, it provides constraints for interpreting branching schemes derived from neontological evidence. Most of the neontological estimates for monkey origins appear to be too old, the fossil evidence suggesting that the origin of the superfamily Cercopithecoidea and the origins of the Colobinae, Papionini and Cercopithecini are younger than usually suggested on neontological evidence. The superfamily is probably no older than 25 m. y., the colobines diverged as a distinctive group about 12–14 m. y. ago, the Papionines about 8–10 m. y. ago and the Cercopithecines perhaps as late as 7 m. y. However, since the Miocene fossil record is rather spotty, these fossil-based estimates may be revised downwards with new discoveries. They are unlikely to be revised upwards. The sequence and timing of cladogenetic events deduced from the east african evidence indicates that all the modern subfamilies arose in Africa, and subsequently spread to Europe and Asia. The sequence of fossil events is in close agreement with neontological evidence such as karyology and molecular anthropology. It is only in the calibration of the sequence that there is disagreement between the fossil and neontological evidence. Strangely, the polarity of the differences in opinion are opposite to those concerning the hominoids, in which the neontological evidence has suggested much younger divergence dates than did the fossil evidence as perceived in the 1960's and 1970's.     

Prospects for Transboundary Marine Protected Areas in East Africa

Transboundary marine protected areas have been proposed in East Africa to tackle threats to marine biodiversity, meet international MPA targets, promote tourism, and contribute to poverty reduction. This article examines what may drive, facilitate, or constrain states in creating a regime for transboundary MPAs. In East Africa, a regime between Mozambique and Tanzania is not yet formed and may be indefinitely delayed due to oil prospecting and exploration. There is, however, a well-developed regime between Mozambique and South Africa that has resulted in the two adjoining MPAs being declared the first transboundary MPA on the continent.     

Green tea extracts as ultraviolet protectants for the beet armyworm,Spodoptera exigua,nucleopolyhedrovirus

The addition of a caffeinated green tea, Camellia sinensis L., filtrate (1%) to the nucleopolyhedrovirus (SeMNPV) of the beet armyworm, Spodoptera exigua (Hübner), provided almost complete protection following UVB irradiation (30 min) in laboratory tests. There were few differences in UV protection when extracts were prepared at 27 or at 90°C. Moreover, few differences in UV protection were demonstrated following infusion times of 5, 15, 30, and 60 min at 90°C. At a 1% concentration, decaffeinated and caffeinated green teas were equally effective as UV protectants. At lower concentrations (0.1, 0.01, and 0.001%) caffeinated green tea provided greater UV protection (UVB/UVB 30, 60 min). Virus/tea extracts (caffeinated), under field conditions at 1 and 5%, were ineffective as UV screens. At a 10% concentration, some UV protection was provided and UV protection further increased in a concentration-dependent manner.     

交配和温度对甜菜夜蛾(Spodoptera exigua)雌蛾性信息素产生的影响

研究表明,交配对甜菜夜蛾雌蛾性信息素各组分的滴度,比例及其在个体间的变异均无显著的影响,因此交配不影响雌蛾在下一暗期的再次求和交配,环境温度对甜菜夜蛾性信息素的产生则有显著的影响,15－25℃最有利于甜菜夜蛾性信息素的产生,而10℃低温和35℃主温则使信息素产生受到明显影响,其中以10℃低温的影响更甚。10℃低温不仅使各组分的滴度产生显著改变,而且使二元性信息素组分的比例受到显著影响,并使二元组分通讯信息的个体间变异明显增大（CV＞10％）,这些改变必半扰乱甜菜夜蛾雌雄间的正常交配。