RFLP analysis of genetic variation in North American populations of the fall armyworm moth Spodoptera frugiperda (Lepidoptera: Noctuidae)

A high level of genetic variability was detected in North American fall armyworm (FA W), Spodoptera frugiperda (J. E. Smith), populations by restriction fragment length polymorphism (RFLP) analysis of genomic DNA. In nearly all cases individual larvae could be differentiated using 22 probe-enzyme combinations. Laboratory colonies formed distinct groups based on RFLP analysis. Individuals from a colony of the previously determined ‘rice strain’ formed a group showing obvious deviation in RFLP patterns from the other five populations, which included a population from a ‘com strain’ colony. The results were consistent with previous studies using allozymes which indicated that there are two genetically differentiated forms of the fall armyworm. Diagnostic markers were also found that distinguish these two groups.     

Using haplotypes to monitor the migration of fall armyworm (Lepidoptera: Noctuidae) corn-strain populations from Texas and Florida

Fall armyworm, Spodoptera frugiperda (J. E. Smith) (Lepidoptera: Noctuidae), infestations in most of North America north of Mexico arise from annual migrations of populations that overwinter in southern Texas and Florida. A comparison of the cytochrome oxidase I haplotype profiles within the fall armyworm corn-strain, the subgroup that preferentially infests corn (Zea mays L.) and sorghum (Sorghum vulgare Pers.), identified significant differences in the proportions of certain haplotypes between the Texas and Florida populations. These proportional differences were preserved as the populations migrated, providing a molecular metric by which the source of a migrant population could be identified. The migratory pattern derived from this method for several southeastern states was shown to be consistent with predictions based on analysis of historical agricultural and fall armyworm infestation data. These results demonstrate the utility of haplotype proportions to monitor fall armyworm migration, and they also introduce a potential method to predict the severity of cotton crop infestations in the short term.     

Genetic characterization of fall armyworm (Lepidoptera: Noctuidae) host strains in Argentina

Fall armyworm is a major economic pest throughout the Western Hemisphere. Previous studies of populations in the southern United States, Brazil, and the Caribbean demonstrated the existence of two morphologically identical but genetically distinct host strains that can only be distinguished using genetic markers, including polymorphisms in the mitochondrial Cytochrome Oxidase I (COI) gene and in the Z-chromosome linked Triose phosphate isomerase (Tpi) gene. The strains differ in some physiological and behavioral characteristics, most notably their preference for different plant hosts, but are capable of hybridizing in the laboratory and in the field. These traits suggest that the strains are in the process of divergence, which may or may not be hemispheric in scope. The objective of this study was to determine whether the two strains are present in Argentina. It was found that the strain-diagnostic haplotypes of the COI and Tpi genes subdivided the Argentina population into two major groups. Each group displayed biases in their distribution among different host plants that were generally consistent with expected strain behavior. The overall results indicated that Argentina fall armyworm exhibit similar genetics and behavior to populations in the rest of the hemisphere. In addition, the Argentina populations had comparable haplotype frequencies to those from Brazil and Texas, consistent with possible interactions with these fall armyworm groups, but appeared to have had minimal exchanges with those from Puerto Rico or Florida.     

Control of the release of digestive enzymes in the larvae of the fall armyworm,Spodoptera frugiperda

There is a basal level of enzyme activity for trypsin, aminopeptidase, amylase, and lipase in the gut of unfed larval (L6) Spodoptera frugiperda. Trypsin activity does not decrease with non‐feeding, possibly because of the low protein levels in plants along with high amino acid requirements for growth and storage (for later reproduction in adults). Therefore, trypsin must always be present so that only a minimal protein loss via egestion occurs. Larvae, however, adjust amylase activity to carbohydrate ingestion, and indeed amylase activity is five‐fold higher in fed larvae compared to unfed larvae. Gut lipase activity is low, typical of insects with a high carbohydrate diet. A flat‐sheet preparation of the ventriculus was used to measure the release of enzymes in response to specific nutrients and known brain/gut hormones in S. frugiperda. Sugars greatly increase (>300%) amylase release, but starch has no effect. Proteins and amino acids have little or no effect on trypsin or aminopeptidase release. The control of enzyme release in response to food is likely mediated through neurohormones. Indeed, an allatostatin (Spofr‐AS A5) inhibits amylase and trypsin, and allatotropin (Manse‐ AT) stimulates amylase and trypsin release. Spofr‐AS A5 also inhibits ileum myoactivity and Manse‐AT stimulates myoactivity. The epithelial secretion rate of amylase and trypsin was about 20% of the amount of enzyme present in the ventricular lumen, which, considering the efficient counter‐current recycling of enzymes, suggests that the secretion rate is adequate to replace egested enzymes. © 2009 Wiley Periodicals, Inc.     

Juvenile hormone biosynthesis in the fall armyworm, Spodoptera frugiperda (Lepidoptera, Noctuidae)

The in vitro production of juvenile hormones (JH) was investigated by using corpora allata (CA) of larvae and corpora cardiaca-corpora allata (CC-CA) complexes of adult females of the fall armyworm Spodoptera frugiperda. In female moths, JH release was high compared to that in 5th and 6th instar larvae. Concentrations of 0.11-0.12 mM methionine, 180-200 mM Na(+), 5.8-8.3 mM K(+), 10-50 mM Ca(2+) and a pH range of 5.7-6.3 yielded optimal incorporation of L-[methyl-(3)H] methionine in vitro by CC-CA complexes. The highest hourly incorporation occurred during a 9-h incubation period following a 1.5-h lag-phase. JH release from CC-CA complexes of adult females was shown to be age-dependent with a peak value on day 2 (approx. 4 pmol h(-1) CA(-1)). By a combination of reversed phase (RP)- and normal phase (NP)-high performance liquid chromatography (HPLC), two major labelled products released by the complex were separated. One compound co-migrated with chemically synthesized JH II diol, the second compound with JH III diol. Only traces of JH II and III could be detected in some samples. Gland extracts also contained both the major radiolabelled products. Double labelling experiments using [3H]methionine and [14C]acetate confirmed their de novo synthesis in CC-CA complexes of female moths. The nature of chemically synthesized reference JH III diol was proved by LC-MS (ESI mass spectrometry) and 1H-NMR (nuclear magnetic resonance spectroscopy).     

Comparison of haplotype frequencies differentiate fall armyworm (Lepidoptera: Noctuidae) corn-strain populations from Florida and Brazil

Fall armyworm, Spodoptera frugiperda (J.E. Smith) (Lepidoptera: Noctuidae), is a major economic pest throughout the Western Hemisphere. Populations can be subdivided into two morphologically identical but genetically distinct strains (corn-strain and rice-strain) that differ in their host plant preferences. These strains can be distinguished by using polymorphisms in the mitochondrial cytochrome oxidase 1 gene. Additional sequence analysis of this locus identified two sites that were highly polymorphic in the corn-strain population and that produced four different haplotype subgroups. Comparisons of the frequency distribution of these haplotypes found no seasonal or plant host specificities, but they did demonstrate that the Brazil corn-strain population is different from corn-strain fall armyworm found in Florida. The development of a rapid means of distinguishing fall armyworm populations originating from Brazil versus Florida provides an opportunity for investigating and comparing the genetic complexity and long-range movements of this important agricultural pest.     

Relationship of flight and reproduction in beet armyworm, Spodoptera exigua (Lepidoptera: Noctuidae), a migrant lacking the oogenesis-flight syndrome

The beet armyworm, Spodoptera exigua, undertakes long-distance migration. We used flight mills to investigate the interaction between flight and reproduction in this species given the apparent absence of the oogenesis-flight syndrome. This syndrome, common in many migratory insects, is characterized by a suite of traits including migration during the pre-oviposition period followed by a switch to oogenesis. No negative effects of inter-ovipositional flight on lifetime fecundity were observed. Instead, adult reproductive output suffered when female flight was initiated the first day after eclosion and before oviposition, suggesting that migratory flight overlaps with the oviposition period rather than being confined to the pre-oviposition period. Mating status of both females and males had no negative influence on their flight performance except that flight distance and flight duration of 7-day-old mated females were significantly less than in unmated females. Furthermore, the number of eggs produced and mating frequency of females less than 7 days of age were not significantly correlated with flight performance, suggesting reproductive development paralleled and was independent of migratory behavior. This independent relationship between flight and reproduction of adults is consistent with the very short pre-oviposition period in this species, and suggests that resources are partitioned between these activities during pupal development. Together, our results uncovered neither obvious trade-offs nor mutual suppression between flight and reproduction in S. exigua, which indicates the lack of an oogenesis-flight syndrome for coordination of these two energy-intensive processes. We propose a conceptual model of migration for this species based on the current and previous studies.     

Isoenzymes and migration in the African armyworm Spodoptera exempta (Lepidoptera, Noctuidae)

Techniques for the separation of proteins have proved to be powerful tools in the study of genetic variation. Polymorphisms on protein levels can be used to study the structure of populations. In general, differences in allele frequencies can be found among populations in different parts of the distribution area of a species. If, however, enough gene flow occurs by migration, the whole system can be regarded as one panmictic unit and similar frequencies can be expected in the whole area.
African armyworms are caterpillars of the noctuid moth Spodoptera exempta. They live on all sorts of graminaceous plants on which vast outbreaks can occur. Their economic importance can be considerable since they eat the main human food crops as well as pasture grasses. The occurrence of migration in S. exempta is known but its importance is a main controversial point. Outbreaks move during the year. These outbreaks could be caused by migrating animals or by increasing local populations when conditions are favourable.
The aim of this study has been to determine the relative importance of migration. Allele frequencies have been determined of six alleloenzymes that proved to be genetically polymorphic, an EST, 0-HBDH, ODH, a-GPDH, ME and LDH. Seventeen armyworm samples have been collected at a maximal distance of 2000 km in Kenya, Tanzania and Rhodesia on different food plants during 1975 and 1976.
No heterogeneity among these samples could be detected in the allele frequencies. A comparison with data from relevant literature on insects showed that the lack of heterogeneity cannot be described to inadequacy of the data. The occurrence of extensive migration is concluded to cause the similarity in allele frequencies.     

New restriction fragment length polymorphisms in the cytochrome oxidase I gene facilitate host strain identification of fall armyworm (Lepidoptera: Noctuidae) populations in the southeastern United States

Several restriction sites in the cytochrome oxidase I gene of fall armyworm, Spodoptera frugiperda (J.E. Smith), were identified by sequence analysis as potentially being specific to one of the two host strains. Strain specificity was demonstrated for populations in Florida, Texas, Mississippi, Georgia, and North Carolina, with an AciI and SacI site specific to the rice (Oryjza spp.)-strain and a BsmI and HinfI site joining an already characterized MspI site as diagnostic of the corn (Zea mays L.)-strain. All four of these sites can be detected by digestion of a single 568-bp polymerase chain reaction-amplified fragment, but the use of two enzymes in separate digests was found to provide accurate and rapid determination of strain identity. The effectiveness of this method was demonstrated by the analysis of almost 200 adult and larval specimens from the Mississippi delta region. The results indicated that the corn-strain is likely to be the primary strain infesting cotton (Gossypium spp.) and that an unexpected outbreak of fall armyworm on the ornamental tree Paulownia tomentosa (Thunb.) Sieb. & Zucc. ex Steud. was due almost entirely to the rice-strain.     

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.     

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.

     

Grass species and endophyte effects on survival and development of fall armyworm (Lepidoptera: Noctuidae)

Grass selections including 10 zoysiagrasses, 18 paspalums, 34 Bermuda grasses, tall fescue, creeping red fescue, and perennial ryegrasses with and without endophyte were evaluated for potential resistance to fall armyworm, Spodoptera frugiperda (J. E. Smith), larvae. Laboratory evaluations assessed the degree of antibiosis among >70 grass lines to first-instar fall armvworms. When all parameters measured were considered, the trend in resistance to fall armyworm among endophyte-infected (E+) and endophyte-free (E-) cool season grasses from greatest to least was: 'Dawson' E+ > APR 1234 > 'Dawson' E- > 'Rosalin' E+ > Lp 5425, 'Rosalin' E-, ATF 480 > 'Tulsa' or: E+ slender creeping red fescue > E+ turf- type perennial ryegrass > E- slender creeping red fescue > E+ forage-type perennial ryegrass > E- forage-type perennial ryegrasses, and E+ tall fescue > E- turf-type tall fescue. Among warm season grasses larval weight gain was reduced on all zoysiagrasses. Larval weight gain also was lower on the Bermuda grasses 'Tifsport', 'Tifgreen', 97-4, 97-14, 97-22, 97-28, 97-39, 97-40,97-54, 98-15, 98-30, and 98-45 than when larvae were fed 'Tulsa' tall fescue or the diet control. Only APR1234 and 'Dawson' creeping red fescue reduced larval survival to the same extent that was observed for zoysiagrasses. Survival on Bermuda grasses was least on 97-8. Seashore paspalums were only rarely less susceptible to fall armyworm than tall fescue, although pupal weights were consistently lower on 'Temple 1' and 'Sea Isle 1' paspalums than that on 'Tulsa' tall fescue. Genetic resistance to key grass pests can reduce insecticide use and simplify management of these cultivars.     

Plant-incorporated Bacillus thuringiensis resistance for control of fall armyworm and corn earworm (Lepidoptera: Noctuidae) in corn

Fall armyworm, Spodoptera frugiperda (J.E. Smith), and corn earworm, Helicoverpa zea (Boddie), perennially cause leaf and ear damage to corn, Zea mays L., in the southeastern United States. Transgenic Bacillus thuringiensis (Bt) hybrids with the Bt11, MON810, or 176 events expressing the Cry1Ab insecticidal endotoxin from were evaluated for control fall armyworm and corn earworm at seven locations in Georgia during 1999 and 2000. Corn was planted at the recommended time for each location and 1 and 2 mo later in the southern locations. All Bt events consistently reduced whorl infestation and damage, although event 176 did not prevent whorl damage in the later plantings in the southern locations in both years. All events also reduced seedling damage by the lesser cornstalk borer, Elasmopalpus lignosellus (Zeller), in one trial and stalk infestations and tunnel length by southwestern corn borers, Diatraea grandiosella Dyar, in another trial. Hybrids containing Bt11 and MON810 events reduced ear infestations in all trials, although reductions were small in later plantings. Nevertheless, both events reduced grain damage from earworms and armyworms by an average +/- SE of 52.5 +/- 5.1% in all trials. The hybrid containing event 176 did not reduce ear infestations and damage. Total grain aflatoxin concentrations were not significantly affected by Bt resistance in any trial (N = 17). Yield responses were variable with the prevention of yield loss being proportional to the severity of insect damage. Although plantings made after the recommended time did not consistently benefit from Bt resistance, Bt11 and MON810 events were effective in reducing damage to field corn when large infestations occurred. The Bt11 and MON810 events mitigated the risk of severe lepidopteran damage to corn, thereby making later plantings of corn feasible in double-cropping systems.     

Genetic basis of resistance to fall armyworm (Lepidoptera: Noctuidae) and southwestern corn borer (Lepidoptera: Crambidae) leaf-feeding damage in maize

Leaf-feeding damage by first generation larvae of fall armyworm, Spodopter frugiperda (J. E. Smith) (Lepidoptera: Noctuidae), and southwestern corn borer, Diatraea grandiosella Dyar (Lepidoptera: Crambidae), cause major economic losses each year in maize, Zea mays L. A previous study identified quantitative trait loci (QTL) contributing to reduced leaf-feeding damage by these insects in the maize line Mp704. This study was initiated to identify QTL and their interactions associated with first generation leaf-feeding damage by fall armyworm and southwestern corn borer. QTL associated with fall armyworm and southwestern corn borer resistance in resistant line Mp708 were identified and compared with Mp704. Multiple trait analysis (MTA) of both data sets was then used to identify the most important genetic regions affecting resistance to fall armyworm and southwestern corn borer leaf-feeding damage. Genetic models containing four and seven QTL explained southwestern corn borer and fall armyworm resistance, respectively, in Mp708. Key genomic regions on chromosomes 1, 5, 7, and 9 were identified by MTA in Mp704 and Mp708 that confer resistance to both fall armyworm and southwestern corn borer. QTL regions on chromosomes 1, 5, 7, and 9 contained resistance to both insects and were present in both resistant lines. These regions correspond with previously identified QTL related to resistance to other lepidopteran insects, suggesting that broad-spectrum resistance to leaf feeding is primarily controlled by only a few genetic regions in this germplasm.     

Using stable isotope analysis to examine fall armyworm (Lepidoptera: Noctuidae) host strains in a cotton habitat

Spodoptera frugiperda (J.E. Smith) (Lepidoptera: Noctuidae), or fall armyworm, is an important agricultural pest of several crops in the Western Hemisphere, including cotton (Gossypium L.). Two morphologically identical host strains of fall armyworm exist that differ in plant host use and habitat distribution. The corn-strain is a primary pest of corn, Zea mays L., whereas the rice-strain is the majority population infesting rice (Oryza spp.) and turfgrass (Cynodon spp.). With the increased use of Bacillus thuringiensis (Bt) toxin-expressing cotton varieties and the necessity of ensuring adequate refuge areas to prevent the spread of Bt toxin resistance, it is crucial to identify the alternative plant hosts available for the fall armyworm population infesting cotton. Stable isotope analysis combined with the molecular analysis of strain-specific markers was used to investigate whether one or both strains routinely develop on cotton grown in the Mississippi delta. We found that the majority of fall armyworm adults present during the early cotton growing season arose from C4 plants (e.g., corn and sorghum, Sorghum vulgare Pers.) and that the only strain likely to be developing on cotton (a C3 plant) in substantial numbers was the corn-strain. The population distribution patterns observed were consistent with corn providing an important refuge for the fall armyworm strain infesting cotton and suggested that late season populations in the Mississippi delta may be migrants from more northern corn areas.     

Influence of whorl region from resistant and susceptible corn genotypes on fall armyworm (Lepidoptera: Noctuidae) growth and development

The effect of diets prepared from whorl tissue of resistant and susceptible corn genotypes, Zea mays L., on the larval growth, development, and physiology of fall armyworm, Spodoptera frugiperda (J. E. Smith), was analyzed. Larvae reared on an optimized artificial diet had a higher growth rate and developed faster than those reared on lyophilized whorl tissue from resistant and susceptible genotypes. Larvae reared on the resistant material were smaller and had a longer developmental period. Larvae reared on yellow-green and green whorl sections from resistant plants were significantly smaller than those reared on the same sections of susceptible plants. There was no significant difference in weight when larvae were reared on the yellow whorl regions from either resistant or susceptible lines. Physiological indices were determined for larvae fed resistant and susceptible lyophilized and fresh whorl material. Larvae fed resistant lyophilized material had significantly lower growth rate (GW) and efficiency of conversion of ingested food to body substance (ECI) than those reared on artificial diet or susceptible material. However, there were no significant differences in consumption index (CI), approximate digestibility (AD) and efficiency of conversion of digested food to body substance (ECD) between larvae reared on lyophilized tissue from resistant and susceptible genotypes. Larvae reared on fresh yellow-green whorl sections from resistant plants had significantly lower GW, ECI, and ECD than those reared on susceptible material. In contrast, no significant differences in any of the estimated food consumption and utilization indices were observed between larvae reared on fresh yellow whorl sections from resistant or susceptible plants. These results suggest that some components of whorls from resistant plants, especially the yellow-green region, inhibit food utilization in fall armyworm larvae.     

Effects of bacillus thuringiensis transgenic corn on corn earworm and fall armyworm (Lepidoptera: Noctuidae) densities

We examined 17 pairs of near-isogenic hybrids of Bacillus thuringiensis (Bt) (176, Mon810, and Bt11) and non-Bt corn, Zea mays L., to examine the effects of Bt on larval densities of Helicoverpa zea (Boddie) and Spodoptera frugiperda (J. E. Smith) (Lepidoptera: Noctuidae) during 2 yr. During ear formation, instar densities of H. zea and S. frugiperda were recorded for each hybrid. We found that H. zea first, second, and fifth instar densities were each affected by Mon810 and Bt11 Bt corn but not by 176 corn. Surprisingly, first and second instars were found in higher numbers on ears of Mon810 and Bt11 corn than on non-Bt corn. Densities of third and fourth instars were equal on Bt and non-Bt hybrids, whereas densities of fifth instars were lower on Bt plants. S. frugiperda larval densities were only affected during 1 yr when second, and fourth to sixth instars were lower on ears of Mon810 and Bt11 hybrids compared with their non-Bt counterparts. Two likely explanations for early instar H. zea densities being higher on Bt corn than non-Bt corn are that (1) Bt toxins delay development, creating a greater abundance of early instars that eventually die, and (2) reduced survival of H. zea to later instars on Bt corn decreased the normal asymmetric cannibalism or H. zea-S. frugiperda intraguild predation of late instars on early instars. Either explanation could explain why differences between Bt and non-Bt plants were greater for H. zea than S. frugiperda, because H. zea is more strongly affected by Bt toxins and more cannibalistic.     

Conventional resistance of experimental maize lines to corn earworm (Lepidoptera: Noctuidae), fall armyworm (Lepidoptera: Noctuidae), southwestern corn borer (Lepidoptera: Crambidae), and sugarcane borer (Lepidoptera: Crambidae)

Plant resistance is a useful component of integrated pest management for several insects that are economically damaging to maize, Zea mays L. In this study, 15 experimental lines of maize derived from a backcross breeding program were evaluated for resistance to corn earworm, Helicoverpa zea (Boddie); fall armyworm, Spodoptera frugiperda (J. E. Smith); southwestern corn borer, Diatraea grandiosella Dyar; and sugarcane borer, Diatraea saccharalis (F.). Experimental line 100-R-3 was resistant in the field to leaf feeding by fall armyworm and line 116-B-10 was resistant in the field to leaf feeding by fall armyworm and leaf and stalk feeding by southwestern corn borer. When corn earworm larvae were fed field harvested silks from experimental line 81-9-B in the laboratory, their pupal weights were significantly lower than the pupal weights of larvae that were fed silks from the resistant control, Zapalote Chico. Maysin levels lower than those commonly associated with corn earworm resistance were present in the resistant experimental line, 107-8-7, indicating a new basis confers resistance to corn earworm in this line. These resistant experimental lines will provide plant breeders with new sources of resistance to lepidopterous insects for the development of improved maize breeding populations.     

Compensatory responses of the fall armyworm (Spodoptera frugiperda) when fed water- and cellulose-diluted diets

Abstract Caterpillars of the noctuid moth, Spodoptera frugiperda (J. E. Smith), reared on artificial diets diluted with cellulose and water, increased fresh weight (fw) consumption 2.2–2.5-fold over those on the undiluted diet. At moderate levels of water- or cellulose-dilution, the increased consumption, combined with increased digestion and absorption of nutrients (ADNU), sufficiently compensated for the reduced nutrient intake to achieve pupal biomass equivalent to that of pupae from the undiluted diet. At higher levels of water- and cellulose-dilution, fw consumption and ADNU increased further but pupal dry weight declined on the water-diluted diets. At each level of dilution fw consumption and ADNU increased similarly on the water- and cellulose-diluted diets, but biomass gain was reduced on the water- compared with the cellulose-diluted diets. This was due in part to lowered food conversion efficiency on the water-diluted diets, possibly caused by increased costs of metabolizing the wetter diets. Our data support the hypothesis that consumption rates are regulated by a nutrient feedback mechanism. Our data also suggest that digestive enzyme activity is correlated with consumption. Furthermore, the cost of increased consumption rates on diets of reduced energetic value may constitute a substantially greater energy expenditure than previously believed. However, this cost was insufficient to reduce relative growth rates but was apparently manifested in lowered lipid accumulation.     

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.