Final Larval Weight Research Articles

Density-dependent development of the yellow mealworm Tenebrio molitor (Coleoptera: Tenebrionidae)

Abstract The increasing global population has led to high food demand and the interest for alternative resources is highly topical. The interest in utilizing insects as a source of food and feed has been rapidly increasing, as the on-growing population has made the need for protein even more demanding. Insect rearing is economically viable, since they can be fed with organic waste and agricultural by-products. The inclusion of bioactive compounds and active ingredients in insect diets has been identified as a potential key factor for enhancing their growth and performance. The aim of this study was to evaluate the effect of a diet enriched with functional ingredients of medicinal and aromatic plants and agricultural by-products of the Greek flora on the growth, survival and development of larvae of the yellow mealworm, Tenebrio molitor (Coleoptera: Tenebrionidae), in the context of larval density-induced stress. Wheat bran enriched with 5%, 10% or 20% of a prepared mixture containing post-distillation residues of medicinal and aromatic plants of the Greek flora (oregano, thyme, sage and rosemary, linseed oil, rock-samphire, industrial cannabis, and olive paste by-product) was evaluated as insect feeding substrate, whereas wheat bran alone (0% enrichment) served as control. Groups of 25, 50, 75 and 100 first instar larvae were separately collected, weighed, and put in cylindrical plastic cups to test if larval density had any effect on survival and development. According to our results, the final larval weight of T. molitor is significantly affected by the density of larvae but not by the rearing substrate. The highest individual weight among all tested substrates was achieved at the density of 25 larvae. Individual weights were highest when larvae were reared on 5% mixture. The weight of those reared on the control substrate was slightly lower, followed by the 10% and 20% mixtures. Larvae fed with 10% enriched substrate showed the highest survival rate, followed closely by those fed with the control and 5% substrates. Our results clearly demonstrate that larval survival is not density dependent, but density is important in the case of individual larval weight.

Fresh aquaculture sludge management with black soldier fly (Hermetia illucens L.) larvae: investigation on bioconversion performances

Aquaculture solid waste (ASW) is a nutrient rich material that can pose a significant environment challenge if not properly managed. This study investigated the potential of black soldier fly (BSF) larvae in converting this waste into biomass. Five substrates comprising chicken feed supplemented with varying proportions of fresh ASW (0%, 25%, 50%, 75%, 100%) were formulated and evaluated for larval growth and waste bioconversion efficiency. High nutrients retention (N: 23.25 ± 1.40%; C: 21.94 ± 0.99%; S: 12.20 ± 1.33%) and feed conversion ratio (1.78 ± 0.08) were detected on substrate 100ASW, although the limited feeding rate (114.54 ± 5.38 mg dry substrate/larvae) and the high amount of indigestible fibres (ADF = 15.87 ± 0.24%; ADL = 6.36 ± 0.17%) were translated to low larval growth (final larval average weight: 66.17 ± 1.81 mg). Decreasing ASW content resulted in reduced fibres and ash, increase in non-fibrous carbohydrates and C/N ratio, and improved larval growth and substrate utilization. However, high larval metabolic activity suggested higher nutrients loss to the environment. Substrate 75ASW demonstrated the best performances in terms of larval production (final larval average weight: 176.30 ± 12.12 mg), waste reduction (substrate reduction corrected by percentage of ASW: 26.76 ± 0.86%) and nutrients assimilation (N: 22.14 ± 1.14%; C: 15.29 ± 0.82%; S: 15.40 ± 0.99%). This substrate closely aligned with optimal BSF rearing substrates reported in literature. Overall, this study highlights the potential of BSF larvae in managing fresh ASW, offering a dual benefit of waste reduction and insect biomass production.

Cross-breeding of Tenebrio molitor strains from a large-scale perspective

Abstract To meet the increased future needs in insect Processed Animal Proteins PAPs, insect sector has to optimize the mass rearing of insects. That being the case, a means to tackle this growing demand for insects is to invest in breeding strategies aiming for the production of hybrids with improved economically and biologically valuable traits. In this framework, the objective of the present study was to evaluate the mating compatibility among four strains of the yellow mealworm, Tenebrio molitor, from different geographical areas (Greece, Belgium, Italy and USA) and to assess and compare the performance of the produced inbred and partially outbred lines. All trials were performed in crates of the size (40 × 60 cm) typically used in industrial rearing of mealworm. Adults of T. molitor were placed in the crates and were left to mate and oviposit. To assess mating compatibility, the amount of oviposited eggs (g) as well as the larval hatching rate were recorded. For the assessment of larval performance of inbred and partially outbred lines, two to three weeks old larvae were placed in crates together with Insectus as feeding substrate. The results showed that all crossed lines demonstrated compatibility, and certain combinations outperformed others as suggested by the high cumulative number of eggs and the larval hatch rates for both inbred and partially outbred lines produced. For hatched larvae, there were significant differences among the inbred and partially outbred lines. The highest hatch rates recorded for the Italian-Italian, Belgian-Italian, and Belgian-USA lines. Concerning offspring performance, all crosses followed a similar pattern in terms of final larval weight. The present study aims to draw the attention of the scientific community and insect producing companies to cross-breeding practices to start unfolding its potential for the genetical improvement of commercially farmed insects.

Mating compatibility and offspring traits evaluation among different strains of Tenebrio molitor.

The fast-growing sector of insects for food and feed stimulates researchers and the industry to explore uncharted territories, such as insect breeding, to improve economically important insect fitness traits. The yellow mealworm, Tenebrio molitor L., is one of the most thoroughly studied insect species as food and feed. However, data on mating compatibility and the effect of cross-breeding between different strains on the performance and fitness of the hybrids are scarce. In the present study, we comparatively evaluated the mating compatibility between two T. molitor inbred strains (Greek and Italian) and their outbred strains, i.e., Italian (♀)-Greek (♂) and Greek (♀)-Italian (♂), as well as the performance of their hybrid offspring. Based on the results, there is good mating compatibility among adults of the strains tested. Offspring performance, quantified as larval survival and final larval weight, followed a similar pattern among the crossings examined. Even though differences were insignificant, the outbreeding of females of the Italian strain resulted in a higher cumulative number of eggs and hatching rate and higher offspring weight. The present study sheds light on the mating compatibility of different T. molitor strains and their hybrids' economically important life table characteristics to take the mass production of insects one step further.

Enriched sewage sludge from anaerobic pre-treatment in spurring valorization potential of black soldier fly larvae

The valorization of sewage sludge by black soldier fly larvae (BSFL) has gained attentions for sewage sludge management since the sludge can be reduced securely as well as larval biomass can be used for biorefineries application. Nevertheless, the BSFL growth was impeded while assimilating nutrition from sewage sludge due to the presence of extracellular polymeric substances (EPS) that had entrapped the essential nutrients inside. Accordingly, the pre-treatment of sewage sludge via anaerobic digestion at different pH was employed in this work to rupture the EPS structure and release more nutrients for larval growth. The results showed that larvae fed with raw sewage sludge had attained the lowest final larval weight (2.05 ± 0.38 mg/larva) as opposed to batches fed with pre-treated sewage sludges. This was because the soluble carbohydrate (more than 6.81 ± 1.31 mg of glucose/g sewage sludge) in EPS was released after anaerobic pre-treatment, facilitating larval assimilation for growth. Furthermore, it was observed that further increasing of pH for sewage sludge pre-treatment had led to lower final larval weight gained due to the inhibitory effect stemming from ammonia production at higher pH. The anaerobic pre-treatment of sewage sludge being executed at pH 3 for 8 days had achieved the highest final larval weight at 7.34 ± 0.97 mg/larva. The still low quality of sewage sludges after the pre-treatment also offered benefit, where high sewage sludge reduction and waste reduction index were recorded due to the necessity of BSFL to consume more sewage sludge in compensating the nutrients destitution in sludge. Lastly, the possibility of predicting final larval weight was successfully materialized via a statistical model derived from the multiple linear regression method. The derived model incorporated the interactive parameters of anaerobic pre-treated pH and durations at various combinations could predict the final larval weight.

Bioconversion and performance of Black Soldier Fly (Hermetia illucens) in the recovery of nutrients from expired fish feeds

In modern aquaculture systems, feed is the main source of the waste being produced, including expired aquafeeds. There is a link between the expiration date of aquafeeds enriched with fish oil for marine fish and the observation of several physical and microbiological changes. Among these, lipid oxidation is worth highlighting, as this process is responsible for the loss of palatability of aquafeeds, which can lead to feeding rejection by the species being farmed. In this study, we used an expired fish aquafeed, which otherwise would be discarded as waste, as a substrate to feed Black Soldier Fly (BSF) larvae. Different replacement levels of expired aquafeed were used which unravelled the amount of n-3 fatty acids added to larval tissues of BSF larvae after 2, 7, and 10 days of feeding. Our results also showed that shorter trials and higher diet replacement levels induced a deleterious effect on final larval weight. Furthermore, amino acid and fatty acid larval contents were shaped by the supplied diet, with results supporting the inclusion of BSF meal in aquafeeds, due to the levels of lysine (5.6–8.9%), methionine (1.9–3.2%), and omega-3 fatty acids (14.5%) recorded. These results demonstrate that the re-introduction of an expired resource aiming to diversify the source of aquafeeds raw materials can be safely achieved through BSF biotransformation. Overall, BSF larvae can successfully recover important nutrients for aquafeeds targeting marine species and foster the production of value-added insects under a circular bioeconomy framework.

Threshold temperatures and thermal requirements of black soldier fly Hermetia illucens: Implications for mass production.

Efforts to recycle organic wastes using black soldier fly (BSF) Hermetia illucens into high-nutrient biomass that constitutes a sustainable fat (biodiesel) and high-quality protein ingredient in animal feeds have recently gained momentum worldwide. However, there is little information on the most suitable rearing conditions for growth, development and survivorship of these flies, which is a prerequisite for mass production technologies. We evaluated the physiological requirements for growth and reproduction of H. illucens on two diets [spent grains supplemented with brewers’ yeast (D1) and un-supplemented (D2)]. Development rates at nine constant temperatures (10–42°C) were fitted to temperature-dependent linear and non-linear day-degree models. Thereafter, life history table parameters were determined within a range of favourable temperatures. The thermal maximum (TM) estimates for larval, pre-pupal and pupal development using non-linear model ranged between 37.2 ± 0.3 and 44.0 ± 2.3°C. The non-linear and linear day-degree model estimations of lower developmental temperature threshold for larvae were 11.7 ± 0.9 and 12.3 ± 1.4°C for D1, and 10.4 ± 1.7 and 11.7 ± 3.0°C for D2, respectively. The estimated thermal constant of immature life stages development of BSF was higher for the larval stage (250±25 DD for D1 and 333±51 for D2) than the other stages evaluated. Final larval wet weight was higher on D1 compared to D2. The population growth rate was most favourable at 30-degree celsius (°C) with higher intrinsic rate of natural increase (rm = 0.127 for D1 and 0.122 for D2) and shorter doubling time (5.5 days for D1 and 5.7 days for D2) compared to the other temperatures. These results are valuable for the optimization of commercial mass rearing procedures of BSF under various environmental conditions and prediction of population dynamics patterns using computer simulation models.

Impact of pH and feeding system on black soldier fly (Hermetia illucens, L; Diptera: Stratiomyidae) larval development.

Black soldier fly (BSF) is a generalist species able to reduce large quantities of organic substrates and is thus considered as an interesting solution for waste management. Moreover, as BSF larvae accumulate high quantities of nutrients during their growth, they are valued because of their potential to produce products such as protein meal or fat for livestock feeds. Abiotic factors can influence larva growth, and a more detailed knowledge and control of these parameters can lead to the development of mass BSF breeding for the production of innovative products for animal feeds. As little information is available on the effects of the pH of substrates and feeding systems, the aim of this study was to evaluate the impact of these two factors on the activities of BSF larvae, prepupae, and adults. An experiment was performed with two fixed factors: i) pH (4.0; 6.1; 7.5; 9.5) and ii) feeding system (batch feeding system (TFS) or daily feeding system (DFS)). The pH treatments impacted larval weight on the first, third, and fifth day, but not at the end of the trial. Larval activity increased pH values from the fourth day onward, with final values of around 8.9–9.4 in all the treatments. The weight of the prepupae ranged from between 0.094 and 0.100 g. The final weight of the larvae and pupae, sex ratio, ingested food, larval mortality, percentage of emergence, and time to reach the pupa stadium were all affected by the feeding system. DFS showed the heaviest final larval weight (0.149 g), but required a longer time (11.3 d) than TFS to reach the prepupa stadium. The findings of this research could be useful for the mass production of BSF. Evaluation of an appropriate feeding system and initial pH value of the substrate are important parameters to reduce the time and to increase the weight in the production of larvae.

Dynamic Effects of Initial pH of Substrate on Biological Growth and Metamorphosis of Black Soldier Fly (Diptera: Stratiomyidae).

Edible insects have become a recognized alternative and sustainable source of high-quality proteins and fats for livestock or human consumption. In the production process of black soldier fly (BSF), (Hermetia illucens L. [Diptera: Stratiomyidae]), initial substrate pH is a critical parameter to ensure the best value of insect biomass, life history traits, and quality bio-fertilizer. This study examined the impact of initial pH values on BSF larvae production, development time, and adult longevity. The BSF were reared on artificial diet with initial pH of 2.0, 4.0, 6.0, 8.0, and 10.0; the control was set at 7.0. Final BSF larval weight was significantly greater in substrates having initial pH 6.0 (0.21 g), control 7.0 (0.20 g), and 10.0 (0.20 g) with no significant difference among them, whereas larval weight reared with initial pH 2.0 and 4.0 were lowest at 0.16 g (-23%). Prepupal weight was greatest when larvae were reared on substrates with initial pH 6.0 (0.18 g), control 7.0 (0.19 g), 8.0 (0.18 g), and 10.0 (0.18 g). In contrast, the prepupal weight of larvae reared on diets with initial pH 2.0 was lowest at 0.15 g (-22%). Larval development time was 21.19 d at pH 8.0, about 3 d (12.5%) shorter than that of those reared on diets with initial pH 6.0, 7.0 control, and 10.0. In all treatments, pH shifted to 5.7 after 3-4 d and 8.5 after 16-17 d except for two groups (2.0 and 4.0) where the pH remained slightly acidic 5.0 and 6.5, respectively.

Early Development of the Threespine Stickleback in Relation to Water pH

Ocean acidification is a growing environmental problem, and there is a need to investigate how the decreasing pH will affect marine organisms. Here we studied the effects of lowered pH on the growth and development of the threespine stickleback (Gasterosteus aculeatus) eggs. Adult fish, collected from the natural environment, were allowed to mate in aquaria and the newly produced eggs were incubated in an experiment. Eggs and larvae from ambient conditions (produced in the laboratory) were reared at three different pH concentrations (control: pH 7.8; and reduced pH treatments: pH 7.5 and 7.0) for 21 days in the laboratory. Dissolved oxygen concentration (8.1 ± 0.1 mg l-1) and temperature (18.6 ± 0.02°C) were monitored regularly. Then, egg diameter, larval length, weight and survival were measured. There was no relationship between egg diameter and pH or oxygen, but a negative relationship was found with temperature. Survival of larvae was not affected by pH or temperature, whereas dissolved oxygen concentration had a positive effect on number of survivors. The pH did not have a significant effect on the final larval length on day 21, but interacted significantly with dissolved oxygen. Higher temperatures were found to have a positive effect on the final larval length and weight. Larval weight, on the other hand, was not related to pH nor oxygen. Coastal zones are characterized by pH levels that fluctuate due to natural processes, such as upwelling and river runoff. Our results suggest that the threespine stickleback larvae are well adapted to the different pHs tested, and egg development will likely not be affected by decreasing pH, but even slight temperature and oxygen changes can have a great impact on the threespine stickleback development.

Effects of temperature and diet on black soldier fly, Hermetia illucens (L.) (Diptera: Stratiomyidae), development

The black soldier fly, Hermetia illucens, is recognised for its use in a forensic context as a means for estimating the time of colonisation and potentially postmortem interval of decomposing remains. However, little data exist on this species outside of its use in waste management. This study offers a preliminary assessment of the development, and subsequent validation, of H. illucens. Larvae of H. illucens were reared at three temperatures (24.9°C, 27.6°C and 32.2°C) at 55% RH on beef loin muscle, pork loin muscle and a grain-based diet (control). Each of the temperatures and diets were found to significantly (P<0.05) affect all stages of immature growth except for pupation time. Overall, those reared on the pork diet required on average ≈23.1% and ≈139.7% more degree hours to complete larval development than those reared on the beef and grain-based diets, respectively. Larvae reared at 27.6°C and 32.2°C required on average ≈8.7% more degree hours to complete development and had a final larval weight ≈30% greater than larvae reared at 24.9°C. The validity of the laboratory larval length and weight data sets was assessed via estimating the age of field-reared larvae. Grain-diet data lacked accuracy when used to estimate larval age in comparison to estimates made with beef and pork-diet data, which were able to predict larval age for ≈55.6% and ≈88.9% of sampling points, respectively, when length and weight data were used in conjunction. Field-reared larval sizes exceeded the maximum observed under laboratory conditions in almost half of the samples, which reduced estimate accuracy. Future research should develop additional criteria for identifying development of each specific instar, which may aid in improving the accuracy and precision of larval age estimates for this species.

Temperature effects on egg and larval development and phenological forecasting of the smaller fruit tortrix,Grapholita lobarzewskii

The effects of temperature on egg and larval development of Grapholita lobarzewskii Nowicki (Lepidoptera: Tortricidae) were studied under controlled conditions to complement the basis for phenological forecasting and thus to optimize the timing of monitoring and control measures with respect to sustainable pest management. Egg development lasted on average 28.1 days at 12.7 °C and 5.5 days at 26.1 °C. Egg mortality was generally low, varying between 12 and 14% within a temperature range of 12.7–22.0 °C, but slightly increased to 20% at 26.1 °C. For egg development, a lower thermal threshold of 9.7 °C and a thermal constant of 90.6 degree days were established. Larval development took on average 76.0 days at 12.7 °C and 21.5 days at 26.1 °C. Larval mortality was 51% at 12.7 °C but only 6–12% at temperatures above 17 °C. The lower thermal threshold and the thermal constant for larval development were 7.6 °C and 389.2 degree days, respectively. Final larval weight increased with temperature from 18.6 mg at 12.7 °C to a maximum of 23.9 mg at 22.0 °C. Based on mortality rates, the optimal temperature range was between 12.7 and 22.0 °C for egg development and between 17.1 and 22.0 °C for larval development, which was confirmed based on the weight of fully grown larvae. These biological parameters of egg and larval development enabled us to parameterise a phenology model for G. lobarzewskii, which was incorporated into an existing decision support system for fruit pests. Precise forecasts of pest phenology facilitate the optimal timing of monitoring and control measures, improve their efficiency, and thereby contribute to sustainable crop protection.

Jasmonic acid-induced resistance to the fall armyworm, Spodoptera frugiperda, in conventional and transgenic cottons expressing Bacillus thuringiensis insecticidal proteins

To assess potential interactions between Bacillus thuringiensis Berliner (Bt) proteins and jasmonic acid (JA)-induced resistance to the fall armyworm, Spodoptera frugiperda Smith & Abbot (Lepidoptera: Noctuidae), three commercial Stoneville cotton cultivars, Gossypium hirsutum L. (Malvaceae) (‘ST 475’, a conventional cultivar; ‘ST 4575 BR’, a Bollgard® cultivar expressing Cry1Ac protein; and ‘ST 4554B2RF’, a Bollgard II® cultivar expressing Cry2Ab2 in addition to Cry1Ac), were treated with JA. Two experiments were conducted with 6-day-old S. frugiperda larvae on three cotton cultivars at two phenological stages. The first experiment was conducted under laboratory conditions and used excised cotton leaves; the second experiment was performed under greenhouse conditions on intact cotton plants. Relative growth rates (RGRs) and leaf area consumed by 6-day-old S. frugiperda larvae were determined for each combination of treatments. Overall, JA treatment and cultivars significantly impacted RGR and leaf area consumption. Significant JA treatment*cultivar interactions were observed for RGR of larvae in the laboratory experiment and for leaf area consumption in the greenhouse experiment. An additional experiment evaluated S. frugiperda neonates on the same JA and cotton cultivar combinations (at a single phenological stage) under laboratory conditions. Neonate survival was determined after 3, 5, and 10 days of feeding, and final larval weight after 10 days of feeding. Overall, JA treatment and cultivars significantly impacted final weight and survival of S. frugiperda. Significant JA treatment*cultivar interactions were observed for final weight and on overall survival of S. frugiperda. Combination of the cotton tissue expressing pyramided Bt proteins with JA treatment demonstrated the greatest negative impact on larval development. Apparent synergism between Bt proteins and JA-induced resistance emphasizes that traditional host plant resistance has a role to play in combination with Bt technology.

Growth Performance of the Red-Stripe Weevil Rhynchophorus schach Oliv. (Insecta: Coleoptera: Curculionidae) on Meridic Diets

Biology and growth performance of Red Stripe Weevil, Rhynchophorus schach Oliv. were studied using meridic diets. The diets consisted of sugarcane (Saccharum officinarum L.) bagasse, copra (Cocos nucifera L.) cake and sago (Metroxylon sagus Rottb.) flour as main ingredients. Larvae or locally known as sagoworm, in copra cake diet exhibited the fastest growth with maximum weight gain of 1609 mg in week 5, while those of sugarcane bagasse diet had slowest growth with peak weight gain of 1024 mg in week 9. Sago flour diet gave the longest larval period at 96.3 days with the highest final larval weight of 8132.1 mg. The R. schach larvae had 8 instars. Head capsule width within each instar was constant irrespective of diets given. Instar period was dependent on diets given and varied from 6.3-12 days. Pupal duration ranged from 38.5-41 days. Adult emergence was 90%. Sago flour diet had the heaviest pupae and adults. Male weevils emerged earlier than the females, but females lived 10-13 days longer. Fecundity was low at 67 eggs per female but the hatchability was 92%. Life cycle for the insect ranged from 130.2-138.8 days, with a lifespan of 178.2-183.8 days. Larvae raised on sago flour diet had the highest fat content at 57.8% but with the lowest fiber at 4.7%. Larvae were generally rich in Mg, Ca, Zn and Fe, but low in Cu. This study showed that sago flour constituted the most suitable diet. The results also suggested that growth and development of the weevil could be further improved by incorporating copra cake and sugarcane bagasse into the sago flour diet. Larvae could be readily mass produced as a source of nutritious food, besides its potential use as a laboratory test organism.

Effect of coconut oil and tricaprylin vs. triolein on survival, growth and fatty acid composition of common carp ( Cyprinus carpio L.) larvae

A 21-day feeding trial was carried out to investigate the ability of first-feeding carp larvae to utilize medium-chain fatty acids (MCFA). Six semi-purified diets, with a common casein and soluble fish protein concentrate basis, were tested on triplicate groups of 400 larvae. The diets were isolipidic (23–24% of dry matter). They differed only by triacylglycerol supplementation (10% of diet) which consisted of either triolein (TO), coconut oil (CO) or tricaprylin (TC) alone or in combination of two of these (TO+CO, CO+TC, TO+TC). Survival and growth rates of larvae fed with CO or TO were high (survival 95–97%, mean wet weight 60–67 mg after 21 days). Addition of TC (5 or 10% of diet) induced a significant mortality as early as 11 days of feeding and resulted in a final survival of less than 6%. TC also led to reduced growth rates (final mean larval weight 6–13 mg). The fatty acid (FA) composition of larvae fed with TO or CO reflected that of the diets with high levels of oleic acid (42% of total FA) in larvae fed with TO and lauric and myristic acids (17 and 10% of total FA, respectively) in larvae fed with CO. In contrast, larvae fed with TC contained only traces (0.3% of total FA) of caprylic acid but had higher levels of capric acid than other larvae (6% vs. 1–2%). Present results indicate an important difference in the utilization between MCFA supplied as CO (12:0) and TC (8:0).

Effects of Sessile Whitefly Nymphs (Homoptera: Aleyrodidae) on Leaf-Chewing Larvae (Lepidoptera: Noctuidae)

The wide distribution, polyphagy, and the often severe effects of whiteflies, Bemisia spp., on their host plants cause a great potential for interspecific interactions between whiteflies and other insect herbivores. Feeding of the silverleaf whitefly, B. argentifolii Bellows & Perring, on collards, Brassica sp., induced high levels of pathogenesis-related proteins (e.g., chitinase, b-1,3-glucanase, peroxidase, and lysozyme) that are considered to play defensive roles against phytopathogens and insect pests. Total protein contents, however, were comparable with those of control plants. Development of cabbage looper larvae, Trichoplusia ni (Hubner), was 20.8% slower on whitefly-infested leaves than on control leaves; relative growth rate was reduced by 18% ( P ≪ 0.01). Final larval weight and survival were not affected by whiteflies. When feeding on whitefly-infested leaves, larvae were found more frequently on the adaxial side of the leaf, which is whitefly-free. The data suggest that early-instar cabbage looper larvae are negatively affected by whitefly infestations, but older instars become omnivores, consuming plant material as well as immature whiteflies. In the field, only 4% of the loopers survived to pupation on whitefly-infested plants, but 18% survived on the whitefly-free plants. The data emphasized the importance of the looper’s larval stage in interspecific interaction and stressed the potentially significant effect of whiteflies on other herbivores in agroecosystems.

The effect of canopy cover and seasonal change on host plant quality for the endangered Karner blue butterfly (Lycaeidesmelissasamuelis).

Larvae of the Karner blue butterfly, Lycaeidesmelissasamuelis, feed solely on wild lupine, Lupinusperennis, from the emergence to summer senescence of the plant. Wild lupine is most abundant in open areas but Karner blue females oviposit more frequently on lupines growing in moderate shade. Can differences in lupine quality between open and shaded areas help explain this disparity in resource use? Furthermore, many lupines are senescent before the second larval brood completes development. How does lupine senescence affect larval growth? We addressed these questions by measuring growth rates of larvae fed lupines of different phenological stages and lupines growing under different shade conditions. The habitat conditions under which lupines grew and plant phenological stage did not generally affect final larval or pupal weight but did significantly affect duration of the larval period. Duration was shortest for larvae fed leaves from flowering lupines and was negatively correlated with leaf nitrogen concentration. Ovipositing in areas of moderate shade should increase␣second-brood larval exposure to flowering lupines. In addition, larval growth was significantly faster on shade-grown lupines that were in seed than on similar sun-grown lupines. These are possible advantages of the higher-than-expected oviposition rate on shade-grown lupines. Given the canopy-related trade-off between lupine␣abundance and quality, maintenance of canopy heterogeneity is an important conservation management goal. Larvae were also fed leaves growing in poor soil conditions and leaves with mildew infection. These and other feeding treatments that we anticipated would inhibit larval growth often did not. In particular, ant-tended larvae exhibited the highest weight gain per amount of lupine eaten and a relatively fast growth rate. This represents an advantage of ant tending to Karner blue larvae.

Combined effects of night‐time temperature and allelochemicals on performance of a generalist insect herbivore

AbstractTo assess the pattern of temperature influencing the effect of allelochemicals on growth of insect herbivores and to examine the potential effect of warmer nights due to global warming, we examined the simultaneous effects of allelochemicals and warmer night‐time temperatures on an insect herbivore (Spodoptera exigua; Lepidoptera: Noctuidae). Dietary chlorogenic acid, rutin and tomatine levels reflected those occurring naturally in the leaves of tomato, a hostplant of this herbivore. We compared the effects of four thermal regimes having a daytime temperature of 26 °C, with the night‐time temperature increased from 14 to 26 °C by increments of 4 °C. The effect of a particular allelochemical on developmental rate was similar among the four thermal regimes. Chlorogenic acid and tomatine each reduced final larval weight, but there was no effect of night‐time temperature. In contrast, rutin had no effect on final weight, whereas final weight declined with increasing night‐time temperature. Night‐time temperature did not influence amount eaten. Larvae ate less when chlorogenic acid or tomatine was in the diet. For each allelochemical, there were no allelochemical by thermal regime interactions. In addition, we compared the effects of allelochemicals and the thermal regime of 26:14 °C and constant 20 °C, which was the average temperature of the 26:14 °C regime. Developmental rate was lower at the constant 20 °C regime, chlorogenic acid and tomatine each depressed developmental rate, and there were no allelochemical by thermal regime interactions. Thus, regardless of the specific allelochemical or amount, the pattern of response at the fluctuating regime was similar to that at the constant temperature. In contrast, comparison of the thermal regime of 26:22 °C and constant 24 °C, which was the average temperature of the 26:22 °C regime, showed several allelochemical by thermal regime interactions. At the 26:22 °C regime, developmental rate was disproportionatly higher at the maximal rutin concentration compared to that at constant 24 °C. At the constant 24 °C, final larval mass was disproportionately lower at the moderate tomatine concentration compared to that at the 26:22 °C regime. Because these results differ from that of other studies examining another species, it appears that the response to incremental changes in night‐time temperature will reflect the allelochemicals and insect species tested. The contrast between the constant 24 °C and 26:22 °C regimes indicates that even small fluctuations (±2 °C ) in temperature over 24 h can yield differences in the response to an allelochemical.

Effects of temperature, multiple allelochemicals and larval age on the performance of a specialist caterpillar

AbstractTo understand the mechanisms underlying plant‐insect herbivore interactions, it is necessary to examine the simultaneous effects of temperature, food quality and larval age. We examined the simultaneous effects of three allelochemicals (tomatine, rutin and chlorogenic acid) on the performance of first and second instar Manduca sexta larvae under two representative thermal regimes 21: 10°C and 26: 15°C for spring and summer, respectively. Thermal regime and allelochemicals interacted to influence the time from egg hatch to ecdysis to the third instar. On average, it took about half as much time to reach the third instar at 26: 15°C as it did at 21: 10°C. Separately, tomatine and rutin had a negative effect on developmental time from egg hatch to the third instar, but their simultaneous effects were not additive. Chlorogenic acid significantly reduced the negative effect of tomatine. The magnitude of the allelochemical effect was larger at the cooler thermal regime compared to the warmer regime. For instance, chlorogenic acid by itself had no effect at the 26: 15°C regime, but at the 21: 10°C regime it significantly shortened total developmental time. The effect of chlorogenic acid on stadium duration was distinctly different for the two instars. Chlorogenic acid shortened stadium duration of first instar larvae. However, depending on thermal regime and the presence of tomatine, chlorogenic acid had a negative, positive or neutral effect on stadium duration of second instar larvae. Molting duration of second instar larvae was shortened by a half day at the warmer thermal regime but was not affected by the allelochemicals. Final larval weight was influenced by rutin and chlorogenic acid. Caterpillars fed diets containing 20 μmoles of rutin were on average 10% lighter than those fed plain diet, whereas those fed diets containing 20 μmoles of chlorogenic adic were on average 7% heavier. However, the effect of chlorogenic acid depended on thermal regime. Overall, our results indicated that: 1) temperature and food quality can interact to influence insect performance and 2) these effects are influenced by larval age.

Simultaneous effects of night-time temperature and an allelochemical on performance of an insect herbivore.

One effect of global warming may be an increase in night-time temperatures with daytime temperatures remaining largely unchanged. We examined this potential effect of global warming on the performance of tobacco hornworm larvae, Manduca sexta (Sphingidae), by manipulating night-time temperature and dietary rutin levels simultaneously under a 12 light:12 dark photoregime. All four thermal regimes (26:14, 26:18, 26:22, and 26:26° C) had a daytime temperature of 26° C, with the night-time temperature increased from 14 to 26° C by increments of 4° C. Dietary rutin levels (0, 10 and 20 μmoles g-1 fresh weight of diet) reflected those occurring naturally in the leaves of tomato, a preferred host plant of M. sexta. With low night-time temperatures (14 and 18° C), rutin had a negative linear effect on developmental rate, relative growth rate and relative consumption rate of the caterpillars. However, at a night-time temperature of 22° C, rutin had a negative non-linear effect. At a night-time temperature of 26° C, rutin had a negative linear impact but less so than at the other nightime temperatures. Likewise, the negative effect of rutin on molting duration was mitigated as night-time temperature increased. Final larval weight decreased linearly with increased dietary rutin concentrations. Total amount of food ingested was not affected by either rutin or thermal regime. As expected, the caterpillars developed faster under an alternating 26:14° C regime than a constant 20° C regime (the average temperature for the alternating regime), but the effect of rutin depended on the thermal regime. Switching daytime and night-time temperatures had no statistically significant effect on caterpillar performance. Overall, the effect of rutin on rates of larval performance was greater at some levels of warmer nights but damped at another level. These results indicate that the potential effect of warmer nights on insect performance is not a simple function of temperature because there can be interactions between night-time temperature and dietary allelochemicals.