Pupal Biomass Research Articles

Black soldier fly larvae efficiently bioconvert the organic fraction of municipal solid waste thanks to the functional plasticity of their midgut

Abstract The saprophagous larvae of Hermetia illucens show promising potential as effective agents for bioconverting organic waste and by-products into valuable biomass. Their capability to efficiently transform organic substrates, varying in nutrient content, origin, texture, and moisture, is strictly correlated with the morphofunctional complexity of their digestive system and the associated microbiota. In addition, post-ingestion mechanisms are set in motion to regulate the midgut activity depending on the feeding substrate, thus ensuring the nutritional requirements of the larvae. This study aims to assess the capability of H. illucens larvae to grow and biotransform the organic fraction of municipal solid waste (OFMSW). In particular, the larvae were reared on substrates mimicking the OFMSW with different nutrient content, and their growth and bioconversion performance, as well as the quality of larval and pupal biomass were evaluated. Our results demonstrate that the nutritional composition of the rearing substrates had minimal impact on the efficiency of the bioconversion process and on the protein, lipid, and chitin content of the insect biomass. This was due to a fine transcriptional regulation of genes encoding enzymes involved in protein, polysaccharide, and lipid digestion in midgut cells. As a consequence, larvae reared on OFMSW with the lowest protein, starch, and lipid content exhibited a significant increase in protease, amylase, and lipase activities. Overall, this study highlights the value of H. illucens larvae in valorising the OFMSW, demonstrating that variations in its composition do not significantly affect the quality of the bioconversion process. These findings hold significant practical implications as current strategies for OFMSW treatment remain unsatisfactory and innovative approaches are needed to enhance bio-waste recycling and reduce the environmental impact of waste management.

Effects of frass from larvae of black soldier fly (Hermetia illucens) and yellow mealworm (Tenebrio molitor) on growth and insect resistance in field mustard (Brassica rapa): differences between insect species and frass treatments

AbstractFrass, a byproduct of insect rearing, has become popular for its potential use in sustainable agriculture. The rapid growth of insect production results in an increased frass output. This study examined the effects of frass as soil amendment on plant growth and resistance to insect herbivory. In greenhouse experiments, Brassica rapa L. (Brassicaceae), was grown in unamended soil (NoFrass; control) or soil amended with frass (2 g kg−1) from larvae of black soldier fly (BSFF), Hermetia illucens L. (Diptera: Stratiomyidae), or yellow mealworm (MWF), Tenebrio molitor L. (Coleoptera: Tenebrionidae). Frass was applied as raw, incubated, or composted frass before seed germination. Plant growth and performance were measured of larvae of root‐feeding Delia radicum L. (Diptera: Anthomyiidae) and shoot‐feeding Plutella xylostella L. (Lepidoptera: Plutellidae). Initially, raw BSFF and MWF reduced the growth of B. rapa and resulted in a smaller leaf area than NoFrass. However, over time, a notable trend emerged. Whereas the difference in leaf area between MWF and NoFrass disappeared, BSFF consistently resulted in a smaller leaf area than MWF and NoFrass. Raw BSFF reduced D. radicum larval survival and pupal biomass and larval survival of P. xylostella. In contrast, raw MWF increased larval survival and biomass of D. radicum and the survival of P. xylostella larvae. Interestingly, incubation of frass in the soil for 16 days before seed germination removed plant growth inhibition and increased plant leaf area, especially for MWF compared to NoFrass. In addition, composting MWF increased leaf growth. Therefore, frass may be used as a sustainable and natural alternative to conventional organic fertilisers, promoting plant growth and enhancing resistance to herbivory. Our results indicate that soil amendment with raw BSFF may negatively impact herbivore performance, whereas raw MWF may enhance herbivore performance.

The nitrogen-dependent GABA pathway of tomato provides resistance to a globally invasive fruit fly.

The primary metabolism of plants, which is mediated by nitrogen, is closely related to the defense response to insect herbivores. An experimental system was established to examine how nitrogen mediated tomato resistance to an insect herbivore, the oriental fruit fly (Bactrocera dorsalis). All tomatoes were randomly assigned to the suitable nitrogen (control, CK) treatment, nitrogen excess (NE) treatment and nitrogen deficiency (ND) treatment. We found that nitrogen excess significantly increased the aboveground biomass of tomato and increased the pupal biomass of B. dorsalis. Metabolome analysis showed that nitrogen excess promoted the biosynthesis of amino acids in healthy fruits, including γ-aminobutyric acid (GABA), arginine and asparagine. GABA was not a differential metabolite induced by injury by B. dorsalis under nitrogen excess, but it was significantly induced in infested fruits at appropriate nitrogen levels. GABA supplementation not only increased the aboveground biomass of plants but also improved the defensive response of tomato. The biosynthesis of GABA in tomato is a resistance response to feeding by B. dorsalis in appropriate nitrogen, whereas nitrogen excess facilitates the pupal weight of B. dorsalis by inhibiting synthesis of the GABA pathway. This study concluded that excess nitrogen inhibits tomato defenses in plant-insect interactions by inhibiting GABA synthesis, answering some unresolved questions about the nitrogen-dependent GABA resistance pathway to herbivores.

Effects of amending soil with black soldier fly frass on survival and growth of the cabbage root fly (Delia radicum) depend on soil type

New approaches to managing the cabbage root fly (Delia radicum L.) are needed because pesticide regulations continue to limit the availability of effective control products. Soil amendment with black soldier fly (Hermetia illucens L.) frass has recently been shown to reduce D. radicum survival. In a greenhouse experiment, soil from a field on which brassicaceous plant species had repeatedly been grown (brassica field soil) was mixed with frass at ratios of 1, 2 or 5 g/kg. In a second greenhouse experiment, 5 g/kg were added to (a) brassica field soil, (b) soil from a different field on which non-brassicaceous species had been rotated (crop rotation field soil) or (c) blocks of potting soil that were later transplanted to unamended field soil. Brussels sprouts (Brassica oleracea L.) plants were grown in amended soil and were infested with D. radicum larvae after 4 weeks. While amendment with 1 or 2 g/kg did not affect D. radicum performance compared with unamended soil, 5 g/kg reduced D. radicum survival and pupal biomass in brassica field soil. In crop rotation field soil, amendment with 5 g/kg reduced pupal biomass but did not reduce D. radicum survival. Amendment with 5 g/kg had no effect on D. radicum performance in potting soil. In general, D. radicum survival was lower in brassica field soil than in either other soil, irrespective of soil amendment. The effects of black soldier fly frass on D. radicum appear to depend on soil type.

An Interesting Relationship between the Insecticidal Potential of Simarouba sp. in the Biology of Diamondback Moth

Alternative methods of insect management are an important field of study for agriculture. The current study aimed to determine the effect of aqueous extracts from Simarouba sp. (AE-S) on the biology of Plutella xylostella and to determine the toxicity of the extract to the nematode Caenorhabditis elegans (an important in vivo alternative assay system for toxicological study). Lyophilized AE-S was chemically investigated by Ultrahigh-performance liquid chromatography tandem mass spectrometry (UHPLC-MS/MS). We evaluated the effect of the botanical extract on the life cycle of P. xylostella, from larval stage to adult stage, at concentrations of 10%, 5%, 1%, 0.1%, 0.05%, and 0.01% and a control. Subsequently, we analyzed the toxicity of the extract in an in vivo model. AE-S showed high amount of phenolic and flavonoid compounds. Six compounds were identified based on UHPLC-MS/MS analysis, including flavanone, kaempferol, 4,5-dimethoxycanthin-6-one, 11-acetylamarolide, ailanthinone, and glaucarubinone. The median lethal time for P. xylostella was estimated to be 96 h in all concentrations of AE-S, and at 120 h, 100% of the individuals were dead. Larvae exposed to AE-S at concentrations of 0.01, 0.05, and 0.1% showed a reduction in leaf area consumption, underdevelopment, and reductions in movement and pupal biomass. The lowest concentrations of AE-S (0.1%, 0.05%, and 0.01%) did not cause mortality in nematodes. Thus, the aqueous extract of Simarouba sp. could be an effective control tool because it mainly acts in the larval stage, the stage at which the insect causes damage to brassicaceae.

Egg-Associated Germs Induce Salicylate Defenses but Not Render Plant Against a Global Invasive Fruit Fly Effectively.

Germs associated with insect eggs can profoundly mediate interactions between host plants and herbivores, with the potential to coordinate plant physiological reactions with cascading effects on insect fitness. An experimental system was established including the oriental fruit fly (OFF, Bactrocera dorsalis) and tomato to examine the functions of egg-associated germs in mediating plant-herbivore interactions. OFF feeding resulted in significantly increased tannins, flavonoids, amino acids, and salicylic acid in the host tomato. These defensive responses of tomato were induced by the egg-associated germs, including Lactococcus sp., Brevundimonas sp., and Vagococcus sp. Tannins and flavonoids had no significant feedback effects on the pupal weight of OFF, while pupal biomass was significantly decreased by tannins and flavonoids in the germ-free treatment. Metabolome analysis showed that OFF mainly induced metabolic changes in carboxylic acid derivatives. Phenylalanine significantly induced downstream metabolic changes associated with phenylpropanoid accumulation. Finally, we conclude that the effects of egg-associated germs played an important role in facilitating OFF population adaptation and growth by mediating plant defenses, which provides a new paradigm for exploring the interaction of plant-pest and implementing effective pest biocontrol.

Life-history traits of black soldier fly reared on agro-industrial by-products subjected to three pre-treatments: a pilot-scale study

Agrarian production generates approximately 190 million tons of agro-industrial by-products (AIBP) per year that are often disposed of without proper treatment, causing health hazards and environmental pollution. The black soldier fly (BSF; Hermetia illucens) has gained popularity as an organic waste recycler owing to its suitability for large-scale insect farming. Despite their valuable components, AIBPs are rich in fibres with low digestibility and provide a breeding ground for potentially pathogenic microbes, which necessitates proper caretaking. This study focuses on a pilot-scale life-cycle analysis of BSF, comparing three different pre-treatments for agro-industrial wastes. We assessed the effect of the pre-treatments on larval and pupal biomass yield and development time of life stages, pupal and adult body properties, adult emergence and sex ratio, and oviposition and fertilization rates. A mix of residues from pasta production and wheat bran (basis substrate, BS; control treatment) was pre-treated using a chemical (with 0.15% potassium sorbate, BSSORB), an organic (with 10% biochar, BSCHAR), and a microbiological (with a 10-day lactic acid fermentation, BSFERM) approach. We report that the BSSORB treatment had the significantly highest larval and pupal biomass yield as well the significantly largest pupae and adults, and the most successful adult emergence but had low oviposition success. BS and BSFERM were similar in terms of larval and pupal biomass yield, BSF development time, pupal and adult body properties, adult emergence, and oviposition. Nonetheless, BSFERM had the highest share of unfertilized eggs. With BSCHAR, BSF developed faster. This study indicates that all treatments have advantages and disadvantages and that thus their application should be selected based on breeding strategy. By analysing and adapting methods that facilitate the conversion of AIBPs to BSF biomass, the treatment of agricultural wastes and by-products can be made more efficient and sustainable.

Silicon-based induced resistance in maize against fall armyworm [Spodoptera frugiperda (Lepidoptera: Noctuidae)

The fall armyworm (Spodoptera frugiperda) is a major economic pest in the United States and has recently become a significant concern in African and Asian countries. Due to its increased resistance to current management strategies, including pesticides and transgenic corn, alternative management techniques have become more necessary. Currently, silicon (Si) is being used in many pest control systems due to its ability to increase plant resistance to biotic and abiotic factors and promote plant growth. The current experiments were carried out at the College of Plant Protection, Gansu Agricultural University, Lanzhou, China, to test the effect of Si on lifetable parameters and lipase activity of fall armyworm and vegetative and physiological parameters of maize plants. Two sources of Si (silicon dioxide: SiO2 and potassium silicate: K2SiO3) were applied on maize plants with two application methods (foliar application and soil drenching). The experiment results revealed that foliar applications of SiO2 and K2SiO3 significantly (P≤0.05) increased mortality percentage and developmental period and decreased larval and pupal biomass of fall armyworm. Similarly, both Si sources significantly (P≤0.05) reduced lipase activity of larvae, and fecundity of adults, whereas prolonged longevity of adults. Among plant parameters, a significant increase in fresh and dry weight of shoot, stem length, chlorophyll content, and antioxidant activity was observed with foliar applications of Si. Root fresh and dry weight was significantly (P ≤ 0.05) higher in plants treated with soil drenching of SiO2 and K2SiO3. Moreover, SiO2 performed better for all parameters as compared to K2SiO3 and control treatment. The study conclusively demonstrated a significant negative effect on various biological parameters of fall armyworm when plants were treated with Si, so it can be a promising strategy to control this pest.

Leaf Extract from Ailanthus altissima Negatively Impacts Life History Aspects in Spodoptera frugiperda (Lepidoptera: Noctuidae)

The need for novel pesticides in agriculture continues to increase, and with it, the need to identify novel phytochemicals with inhibitory properties against lepidopteran pest species. The invasive tree species, Ailanthus altissima (Mill.) Swingle (Sapindales: Simaroubaceae), has become well established in North America. However, the impact of its secondary metabolites on lepidopteran pests has not been well established. The purpose of this study was to examine the impact of water-soluble secondary metabolites from A. altissima on the life-history aspects of the agricultural pest, Spodoptera frugiperda J.E. Smith (Lepidoptera: Noctuidae). Laboratory reared S. frugiperda were fed artificial diets with or without water-soluble extract from A. altissima. Extract fed S. frugiperda exhibited delays in time to pupation and emergence in addition to reduced larval and pupal biomass as well as relative growth rates. Reduced food consumption was observed and fewer larvae survived to emergence if fed a diet containing A. altissima extract. Further, these adult moths had reduced biomass and smaller wings compared to larvae fed a control diet. Therefore, we suggest that A. altissima metabolites present in the aqueous extract derived from vegetative tissues have detrimental impacts on life-history aspects of S. frugiperda, and in fact, may represent a source of interesting candidate pesticide metabolites. Further studies will investigate the specific metabolites with feeding deterrent properties present in the water-soluble fraction of A. altissima.

Aqueous Extracts of Species of the Genus Campomanesia (Myrtaceae) Affect Biological Characteristics of Plutella xylostella (Linnaeus, 1758) (Lepidoptera: Plutellidae)

Plutella xylostella (Linnaeus, 1758) (Lepidoptera: Plutellidae) is an insect pest that causes great damage to Brassica cultures. It is necessary to develop alternative control methods, because this pest is resistant to many synthetic insecticides that are harmful to the environment. The objective of this study was to evaluate the effects of aqueous extracts of Campomanesia adamantium, C. guazumifolia, and C. xanthocarpa on the life cycle of P. xylostella. These aqueous extracts were prepared in a concentration of 10 g/mL and then applied on cabbage disks of 4 cm2 to feed the larvae until they reached pupal stage. The disks were evaluated daily during the larval stage and replaced every 24 hours. The experiment consisted of ten replicates, each replicate containing five subsamples. The parameters evaluated were larval and pupal survival, pupal biomass, gender ratio, male and female longevity, number of eggs, fecundity, oviposition period and egg survival. The C. xanthocarpa extract increased larval stage and decreased pupal biomass and oviposition period. The C. adamantium extract decreased larval duration, pupal biomass, male longevity, and oviposition period. The C. guazumifolia extract decreased larval stage, male longevity, and oviposition period. The chemical composition of the extracts of Campomanesia species presented flavonoids such as quercetin, phenolic compounds, and tannins, and the highest retention time occurred in C. adamantium. Thus, the extracts of Campomanesia species were effective in decreasing and controlling the oviposition period of P. xylostella, probably because of the presence of flavonoids, which indicates a possible antioxidant potential and, therefore, the observed antibiosis.

Parasitism of Lepidopteran Defoliators of Urban Plants byPalmistichus elaeisis(Hymenoptera: Eulophidae)

Heraclides anchisiades capys (Lepidoptera: Papilionidae), Citioica anthonilis (Lepidoptera: Saturniidae), and Methona themisto (Lepidoptera: Nymphalidae) are tree and shrub pests commonly found in urban areas. The parasitism capacity of Palmistichus elaeisis (Hymenoptera: Eulophidae) was evaluated on pupae of these lepidopteran pests as well as on 2 commonly used alternative hosts, Anticarsia gemmatalis (Lepidoptera: Noctuidae) and Tenebrio molitor (Coleoptera: Tenebrionidae). The number of parasitoids produced per mg of host pupal biomass was significantly greater on H. anchisiades capys and T. molitor compared with the other 3 lepidopteran species. The mean number of parasitoids emerging per host pupa was also significantly more on H. anchisiades capys compared with C. anthonilis, M. themisto, A. gemmatalis, or T. molitor. All host species tested in this study show the potential to be used in mass rearing P. elaeisis in the laboratory. However, the lower parasitism and emergence of P. elaeisis on H. anchisiades capys pupae suggests that this lepidopteran pest may not be a suitable host for this parasitoid in the field.

Larval development of Spodoptera eridania and Spodoptera frugiperda fed on fresh ear of field corn expressing the Bt proteins (Cry1F and Cry1F + Cry1A.105 + Cry2Ab2)

ABSTRACT: The objective of this study was to evaluate extent of larval period, larval survival (%), food consumption, and pupal biomass of Spodoptera eridania and Spodoptera frugiperda (Lepidoptera: Noctuidae ) fed on fresh ears of field corn expressing Bt proteins (Cry1F and Cry1F+Cry1A.105+Cry2Ab2). Larvae of Spodoptera spp. survived less than two days when they consumed Bt corncobs and showed 100% mortality. Spodoptera eridania reared on non-Bt corn cobs showed higher larval development (21.6 days) than S. frugiperda (18.4 days) and lower viability (56.4% and 80.2% for S. eridania and S. frugiperda , respectively). A higher amount of corn grains was consumed by S. eridania (5.4g) than by S. frugiperda (3.9g). In summary, this study demonstrated that the toxins Cry1F and Cry1F + Cry1A.105 + Cry2Ab2 expressed in fresh corn cobs contributed to protect ears of corn against S. frugiperda and the non-target pest S. eridania . However, itis important to monitor non-Bt cornfields because of the potential of both species to cause damage to ear sof corn.

English

The objective of this study was to evaluate the effects of the methanolic extracts from the leaves, bark and flowers of Trichilia silvatica on Spodoptera frugiperda. Also, it was use in evaluating the total phenolic and flavonoid content of methanolic extracts. We also reported chemical study on the most active extract. Corn leaves were immersed in a 1% methanolic extract solution and fed to second instars of S. frugiperda. The extract of the T. silvatica (LTS) leaves decreased the viability of the larva, prolonged larval duration, affected the pupal biomass, decreased the period of oviposition and the number of eggs as well as affected the egg viability. The methanolic extract of the T. silvatica (BTS) bark decreased the larval viability, oviposition period, number of eggs and egg viability. The flower extract of T. silvatica (FTS) decreased the larval viability and period of oviposition. In relation to the constituent contents, the methanolic extract of the leaves showed highest total phenol (233.37 mg gallic acid/g of extract) and flavonoid (53.17 mg quercetin/g of extract) content. The chemical study of the FTS resulted in α-tocopherol, sitosterol 3-O-glucopyranoside, mustakone and N-metilproline. Our results indicate that the extracts affected the biology of S. frugiperda, with LTS being the most promising.   Key words: Meliaceae, methanolic extracts, insecticides, plant-derived compounds.

Crop damage increases with pest species diversity: evidence from potato tuber moths in the tropical Andes

Summary 1. Insect pests in agricultural systems are one of the major causes of damage to crop production and storage worldwide. However, the study of the effect of multiple pests on agricultural productivity has remained largely disconnected from the ongoing debate on how species diversity affects the productivity of ecosystems. The aim of our study is to use information from crop studies to inform the debate on species diversity and ecosystem productivity. 2. We present the results of an experimental study that manipulated the species richness of three tuber feeding moth species (Lepidoptera: Gelechiidae) at constant larval density. We measured the influence of this manipulation on (1) damage to the economically most important crop in the Andean region, the potato Solanum tuberosum and (2) the performance of the moths as a consequence of feeding rates. 3. Our results showed that the three pest species together cause more damage to the crop than is predicted from the effects of each pest alone. This resulted in significant increases in pupal biomass and fecundity. 4. Potential mechanisms to explain our results are (1) more complete resource utilization and thus greater crop damage (feeding complementarity) and (2) negative interactions, where intra‐specific interactions are greater than inter‐specific interactions. 5. Synthesis and applications. Our findings may have important consequences for integrated pest management in poor tropical countries. Biodiversity in many tropical countries is decreasing rapidly, leading to reductions in ecosystem services such as biocontrol and pollination. At the same time an increasing number of species, many of them agricultural pests, are being introduced by humans. Our results show that the potential complementarity effects among pest species may increase damage to field crops to a larger extent than previously expected. Control strategies to limit the introduction of new pest species are therefore urgently needed in these countries where the daily management of biological resources is largely in the hands of poor rural people and local government staff with limited funding.

Reciprocal interactions between the cabbage root fly (Delia radicum) and two glucosinolate phenotypes of Barbarea vulgaris

AbstractThe cabbage root fly, Delia radicum L. (Diptera: Anthomyiidae), has a life cycle with spatially separated components: adults live and oviposit above ground, whereas larvae feed and pupate below ground. Oviposition choice is affected by shoot glucosinolates. However, little is known about below‐ground plant defence against D. radicum. Here, we investigate the effect of glucosinolates on oviposition preference and performance of D. radicum, using two naturally occurring heritable chemotypes of Barbarea vulgaris R. Br. (Brassicaceae) with different glucosinolate profiles: BAR‐type plants (the most common and genetically dominant glucosinolate profile, dominated by glucobarbarin) and NAS‐type plants (the recessive phenotype, dominated by gluconasturtiin). Performance was studied by applying 10 neonate D. radicum larvae per plant and measuring pupal biomass after 18 days. There was no difference in retrieval, but pupae had a higher biomass after development on BAR‐type plants. On average, BAR‐type plants received 1.8 times more eggs than NAS types, but this difference was not statistically significant. In a separate experiment, we compared the physiological response of both chemotypes to D. radicum feeding. Infestation reduced root and shoot biomass, root sugar and amino acid levels, and shoot sugar levels. Except for shoot sugar levels, these responses did not differ between the two chemotypes. Shoot or root glucosinolate profiles did not change on infestation. As glucosinolate profiles were the only consistent difference between the chemotypes, it is likely that this difference caused the reduced biomass of D. radicum pupae on NAS‐type plants. In an experimental garden, plants were heavily infested by root flies, but we found no differences in the percentage of fallen‐over flower stalks between the chemotypes. Overall, we found more pupae in the soil near BAR‐type plants, but this was not statistically significant. The results of the performance experiment suggest that BAR‐type plants may be more suitable hosts than NAS‐type plants.

Starvation Effects on Larval Development of Beet Armyworm (Lepidoptera: Noctuidae)

Sporadic starvation of herbivorous insect pests, such as the beet armyworm Spodoptera exigua (Hübner), often occurs due to host plant scarcity and dislodgement from host plants resulting from inclement weather, enemy attack, and other perturbations. We hypothesized that (1) starvation of beet armyworm in earlier instars would increase the possibility of undergoing supernumerary instars greater than would be the case for later instars; and (2) starvation of beet armyworm in earlier instars would prolong developmental time more than starvation in later instars. We tested these hypotheses by starving beet armyworm larvae for 48 h in the first, third, and fifth instars, and monitoring their development. Beet armyworms normally have 5 instars before pupation. Significantly more larvae underwent 6 larval instars (20.22 ± 4.35%) when starved for 2 d in the first instar compared with those starved for 2 d in the third (2.0 ± 2.00) and fifth instars (0.0), and relative to unstarved larvae (0.0). The number of instars that S. exigua larvae will experience can be predicted as early as the third instar-head capsule widths in this instar clearly differentiate for those destined to experience 5 and 6 instars. Developmental times of starved larvae also were prolonged compared with unstarved larvae. Developmental times (mean ± SE in days) of larvae starved in the first instar (20.32 ±0.16) were significantly longer than those starved in the third (17.04 ± 0.20) or fifth instars (16.92 ± 0.10), or than unstarved larvae (14.62 ± 0.25). Timing of starvation significantly affected the pupal weight of larvae undergoing 5 instars. This suggests that (1) starvation of 2 d in very early instars (the first instar) increases the pupal weight at the cost of prolonged developmental time; and (2) starvation of 2 d in later instars (the fifth instar) leads to lower pupal biomass, presumably because of inability to compensate for the loss.

Influence of dietary nutritional composition on caterpillar salivary enzyme activity

Caterpillars are faced with nutritional challenges when feeding on plants. In addition to harmful secondary metabolites and protein- and water-limitations, tissues may be carbohydrate-rich which may attenuate optimal caterpillar performance. Therefore, caterpillars have multiple strategies to cope with surplus carbohydrates. In this study, we raise the possibility of a pre-ingestive mechanism to metabolically deal with excess dietary sugars. Many Noctuid caterpillars secrete the labial salivary enzyme glucose oxidase (GOX), which oxidizes glucose to hydrogen peroxide and gluconate, a nutritionally unavailable carbohydrate to the insect. Beet armyworm, Spodoptera exigua, larvae were restricted to diets varying in protein to digestible carbohydrate (P:C) ratio (42p:21c; 33p:30c; 21p:42c) and total nutrient concentration (42% and 63%). High mortality and longer developmental time were observed when caterpillars were reared on the C-biased, P-poor diet (21p:42c). As the carbohydrate content of the diet increased, caterpillars egested excess glucose and a diet-dependent difference in assimilated carbohydrates and pupal biomass was not observed, even though caterpillars restricted to the C-biased diet (21p:42c) accumulated greater pupal lipid reserves. Larval labial salivary GOX activity was also diet-dependent and gluconate, the product of GOX activity, was detected in the frass. Unexpectedly, GOX activity was strongly and positively correlated with dietary protein content.

Fecundity and egg distribution of the herbivore Spodoptera pectinicornis as influenced by quality of the floating aquatic plant Pistia stratiotes

AbstractWe determined the influence of larval host quality of the floating aquatic weed Pistia stratiotes L. (Araceae) on the fecundity and egg distribution of the biological control agent Spodoptera pectinicornis (Hampson) (Lepidoptera: Noctuidae). Different nutritional levels were produced by growing plants with relatively low and high levels of nitrogen, phosphorus and potassium fertilizer. Female and male pupal biomass were significantly greater when the larvae were fed leaves from the high fertilizer plants. Although the fertilizer treatments did not significantly influence total fecundity, there was an indirect effect as adults from larger pupae were more fecund. Regardless of treatment, ovipositing females formed a depression in the leaf surface by removing trichomes into which they deposited the egg masses. Most of the egg masses were laid on the lower leaf surface, on leaf positions 5–8 (counting from the young inner to the outer leaves) and during days 1–2 post‐eclosion. Most of the eggs were laid in masses but about 12% were solitary. Females fed the low fertilizer treatment laid a greater proportion (mean ± s.e.) of their eggs as solitary eggs (17.3 ± 3.4% of total eggs) than did females fed the high fertilizer treatment (8.3 ± 2.3% of total eggs). The increased percentage of solitary eggs laid by the females from the low quality larval diet may be an adaptive response to decrease competition among the progeny.

Protandry in Delia antiqua (Diptera: Anthomyiidae)

Sex differences in the duration of egg-larval and pupal stages, and in eclosion curves were examined under 3 different temperature regimes in the laboratory to assess the likelihood of protandry as an adaptive strategy for the onion maggot, Delia antiqua (Meigen). Significant sex differences in development time of larval and pupal stages were evident when eggs were reared at constant (22°C) or alternating (12-22°C) temperature. When male egg development was delayed 24 h by storage at 4°C, followed by 22°C, mean larval development time was significantly greater, but pupal biomass and development time were significantly lower, suggesting variation in relative larval growth rates between the sexes. Under nondiapause conditions, male pupae weighed significantly less than females, but pupal weight was only weakly correlated with larval development. Eclosion of diapause male pupae occurred over a shorter interval (4 d) than from nondiapause pupae (9-12 d), but protandry resulted from disparate pupal development times between the sexes alone, because sexual dimorphism of pupal weight was not apparent. The hypothesis that protandry is an adaptive strategy providing reproductive benefits to either sex is equivocal for D. antiqua because eclosion curves of pupae were normally distributed and mean time lags in eclosion peaks between the sexes were too short (<4 d) to optimize any reproductive benefits from early sexual maturation or mating. The alternative hypothesis is presented that protandry is a nonadaptive outcome of selection for other life history traits that is unbiased by female size dimorphism.

Fecundity, reproductive effort, and pupal size in the profundal midgeChironomus cuccini (Diptera: Chironomidae)

Fecundity ofChironomus cucini increased linearly across a three-fold range of female pupal biomass. Females from a lake producing small pupae (Crystal Lake) had an average of 303 primary follicles, while larger pupae from Trout Lake had an average fecundity of 582. Pupae produced in Crystal Lake from larvae that received experimental food supplements were intermediate in size and fecundity. Pupal biomass explained 76% of the variation in fecundity. No difference in egg size was detected between pupae from the two lakes, and an average value of 2.1 μg egg−1 was used to calculate the total biomass allocated to eggs in each of 79 females dissected. This measure of reproductive effort scaled isometrically with pupal mass. On average, females allocated 48% of their biomass to eggs and 52% to somatic tissues. A comparison of average male biomass to female somatic biomass across 12 populations indicated that the biomass difference between the sexes is a biased predictor of fecundity.