Influence of sex and dietary fat on the group effect in larvae of Acheta domesticus (L.)

Larvae of Acheta domesticus show the group effect when reared in pairs on an artificial diet with the opposite sex, but not when reared with the same sex. When wheat-germ oil is added to the artificial diet, all paired larvae exhibit the group effect, regardless of sex. Dietary fat also improves survival and growth, but the identity of the component(s) producing these results has not been determined. The possible roles of linolenic acid and linolenic acid synthesis in this insect are discussed.     

Protein synthesis and uric acid excretion in the absence of essential amino acids in the silkworm,Bombyx mori

Effects of omission of single essential amino acids in the diet on incorporation of [¹⁴C]-labelled amino acid into tissue protein and on excretion of uric acid in the silkworm, Bombyx mori, were investigated. When larvae were reared on the diet deficient in isoleucine, the [¹⁴C]-leucine incorporated into tissue protein was less than that incorporated in larvae reared on the complete diet. This decrease of incorporation was also observed when any one of ten essential amino acids were omitted singly. This was accompanied by an enhanced excretion of uric acid by the larvae.     

Responses of Mamestra brassicae (Lepidoptera: Noctuidae) to crowding: interactions with disease resistance,colour phase and growth

This study examines phenotypic plasticity in relation to rearing density in larvae of the moth, Mamestra brassicae. Larval phase, growth rate, weight at moulting and susceptibility to disease were quantified when reared at five densities. Larvae develop more quickly, but attain a smaller size and are more susceptible to disease, when reared at high than at intermediate densities. They also exhibit a higher degree of melanisation than larvae reared at intermediate densities, or singly. A review of the literature suggests that a switch to a rapidly developing dark phase at high densities is a widespread phenomenon within the Lepidoptera. Rapid development at the expense of attaining a large size, and increased melanisation, are interpreted as adaptive responses to reach pupation before food supplies are depleted, as is likely when larval density is high. High susceptibility to viral infection at high density may be a result of physiological stress associated with rapid development, or due to a shift in allocation of resources from resistance to development: larvae that developed quickly were more susceptible to infection. Larvae reared singly appeared to be less fit than larvae reared at intermediate densities: they exhibited many of the characteristics of larvae reared at high density, particularly low weight, a right-hand skew in their weight frequency distribution, and high susceptibility to disease. I hypothesise that expression of resistance may be phenotypically plastic with regard to environment. Contact with other larvae may, up to a point, stimulate both growth and resistance to infection, for the risk of infection will increase with the density of conspecifics.     

Development and Leaf Consumption by Spodoptera cosmioides (Walker) (Lepidoptera: Noctuidae) Reared on Leaves of Agroenergy Crops

Spodoptera cosmioides (Walker) (Lepidoptera: Noctuidae) is a polyphagous pest that threatens more than 24 species of crop plants including those used for biodiesel production such as Ricinus communis (castor bean), Jatropha curcas (Barbados nut), and Aleurites fordii (tung oil tree). The development and leaf consumption by S. cosmioides reared on leaves of these three species were studied under controlled laboratory conditions. The egg-to-adult development time of S. cosmioides was shortest when reared on castor bean leaves and longest when reared on tung oil tree leaves. Larvae reared on castor bean and Barbados nut leaves had seven instars, whereas those reared on tung oil tree leaves had eight. Females originating from larvae reared on castor bean and Barbados nut leaves showed greater fecundity than did females originating from larvae reared on tung oil tree leaves. Insects fed on castor bean leaves had shorter life spans than those fed on tung oil tree and Barbados nut leaves although the oviposition period did not differ significantly. The intrinsic and finite rates of increase were highest for females reared on castor bean leaves. Total leaf consumption was highest for larvae reared on tung oil tree leaves and lowest for those reared on Barbados nut leaves. We conclude that castor bean is a more appropriate host plant for the development of S. cosmioides than are Barbados nut and tung oil tree.     

Ontogenetic isolation favours sibling cannibalism in mites

Inclusive fitness theory suggests that cannibalistic individuals should preferentially eat unrelated prey when given a choice between related and unrelated individuals. Using the predatory mite Phytoseiulus persimilis, I investigated whether having contact with siblings during a sensitive ontogenetic phase or not determines whether cannibalistic protonymphs tend to eat more sibling or nonsibling larvae in choice situations. Cannibals reared with siblings preferentially ate nonsibling larvae when these had been reared in a sibling group but showed no preference when the larvae had been reared in isolation. Cannibals reared in isolation showed no preference when the larvae had been reared in a sibling group and preferentially ate sibling larvae when these had been reared alone. The occurrence of preferential sibling cannibalism when both cannibal and prey had been reared in isolation suggests the use of self-referent phenotype matching to distinguish between siblings and nonsiblings.     

Growth and fatty acid composition of freshwater prawn, Macrobrachium rosenbergii, larvae fed diets containing various ratios of cod liver oil–corn oil mixture

A feeding trial was conducted to determine the effect of replacing costly cod liver oil with corn oil as a source of dietary lipid on the growth and fatty acid composition of the larval freshwater prawn, Macrobrachium rosenbergii de Man. Prawn larvae were weaned to artificial diets containing cod liver oil and corn oil either singly or in various combinations (2 : 1, 1 : 1, 1 : 2, w/w). Weaning to artificial diets from Artemia nauplii commenced at larval stage III with complete substitution by stage X. The reference group was reared solely on Artemia nauplii during the entire experiment. Incorporation of corn oil at 33–67% of dietary supplemental oil did not have significant effects on the post‐larval production. However, larvae fed with corn oil alone revealed a significantly lower post‐larval production compared to other experimental diets as well as to the reference group. No significant differences (P > 0.05) were observed in dry weight, protein and lipid concentration among larvae fed on various dietary treatments. Palmitic (16 : 0) and oleic/vaccenic (18 : 1) acids were the dominant saturated and monounsaturated fatty acids in larval tissues, respectively, whereas the polyunsaturated fraction was dominated by eicosapentaenoic (20 : 5n‐3) acid. The polyunsaturated fatty acid composition was dominated by n‐3 acids rather than n‐6 fatty acids. The fatty acid composition of the prawn in general reflected that of the diet. Larvae on diets containing higher concentrations of corn oil rich in linoleic (18 : 2n‐6) acid showed a higher concentration of this acid in their tissues. No evidence of de novo synthesis of linoleic (18 : 2n‐6) acid was found. Higher levels of stearic (18 : 0), arachidonic (20 : 4n‐6) and eicosapentaenoic (20 : 5n‐3) acids found in larvae as compared with those fed Artemia and artificial diets strongly indicated the larval ability in chain elongation and desaturation of palmitic (16 : 0), linoleic (18 : 2n‐6) or linolenic (18 : 3n‐3) acids, respectively. Despite a large variation of n‐3 to n‐6 ratios of the live and artificial diets, larval n‐3 to n‐6 ratios were relatively stable among different dietary treatments, possibly indicative of the importance of such a ratio in the larval fatty acid metabolism.     

Density-related variation in vertical transmission of a virus in the African armyworm

Larvae of the African armyworm, Spodoptera exempta, are darker and more resistant to baculovirus infection when reared in groups (gregarious form) compared to being reared singly (solitary form). Lepidoptera that survive virus challenge as larvae could potentially retain a sublethal virus infection which is then transmitted vertically to the next generation. Here we examine whether gregarious and solitary forms of the armyworm differ in the costs of surviving virus infection and in their capacity to transmit an active baculovirus infection to their offspring. Pupae of larvae reared gregariously that survived virus challenge weighed significantly less than uninfected individuals, but this was not so for those reared solitarily. This did not, however, translate into differences in fecundity, at least under laboratory conditions. As found in previous studies, pre-oviposition period was shorter for solitary than gregarious insects, and it was also shorter for females that had been challenged with virus as larvae. Both the prevalence of egg batches containing larvae that died from nucleopolyhedrovirus (NPV) infection and the proportion of infected larvae within each egg batch were significantly increased (approximately doubled) when parental moths were previously challenged with the virus during their larval state. This demonstrates that horizontal transmission in one generation can elevate vertical transmission to the next generation. Moreover, prevalence of overt infection in the offspring generation was two to three times greater when parental moths were reared solitarily as larvae than when reared gregariously. Disease prevalence and proportional infection were both independent of the sex of the infected parent and whether or not the egg batch was surface-sterilized to remove potential contaminants. This suggests that the eggs are infected internally (transovarial) rather than externally (transovum). These results help to shed light on the observed temporal pattern of virus epizootics in eastern Africa.     

Amino acid requirements of the mosquito Culex pipiens: asparagine essential

When any of the ten “rat essential” amino acids was omitted singly from a fully-defined synthetic dietary medium, newly-hatched Culex pipiens larvae were unable to develop to the second instar. With proline omitted, development was greatly retarded and survival to the adult stage reduced. Without aspargine (but not aspartic acid) growth and development ceased in most individuals before larval-pupal ecdysis, and no adults were obtained. These twelve amino acids are considered nutritionally essential for this mosquito. With glycine omitted singly, development was markedly retarded, but survival to the adult stage was not affected; thus this amino acid is required for good growth, but these experiments do not demonstrate it as essential. Single omission of alanine, aspartic acid, cysteine, glutamic acid or amide, serine or tyrosine had virtually no effect on development and they are therefore considered nutritionally non-essential. With diets containing the twelve culex-essential amino acids only, very little development occurred, but augmentation with either glycine or serine allowed growth and development almost as good as with the complete amino acid mixture. Augmentation of the essential twelve with alanine, cysteine, glutamic acid/amide, or tyrosine singly failed to improve development. The requirement for dietary asparagine shown by these studies appears to be unique among insects so far studied. In particular, another mosquito, Aedes aegypti, has no such requirement.     

The rôle of amino acids in diet intake and selection and the utilization of dipeptides by Aphis fabae

Eight amino acids considered essential for the growth of Aphis fabae were investigated in relation to their rôle in protein synthesis and phagostimulation. When either alanine, histidine, methionine, proline, or serine were omitted from synthetic diets, intake was lower than that of the complete diet over a 4 day period. The omission of cysteine, phenylalanine, or tyrosine failed to reduce diet intake. Histidine and methionine were considered essential for protein synthesis and did not act as phagostimulants; alanine and proline, however, appeared to act primarily as phagostimulants. When subjected to choice chamber tests aphid larvae had a severely limited ability to select between complete diets and ones deficient in a single amino acid. If methionine and glycine were replaced by either glycyl l-methionine or l-methionyl glycine the size attained by larvae during growth was less than that of aphids reared on a complete diet but greater than that of aphids reared on diets deficient in both dipeptides and methionine.     

Are stag beetles fungivorous?

Stag beetle larvae generally feed on decaying wood; however, it was unknown whether they can use wood-rotting fungi alone as food. Here, to clarify this, newly hatched larvae of Dorcus rectus (Motschulsky) (Coleoptera: Lucanidae) were reared for 14 days on artificial diets containing a fixed amount of freeze-dried mycelia of the following fungi: Bjerkandera adusta, Trametes versicolor, Pleurotus ostreatus, and Fomitopsis pinicola. The mean incremental gain in larval body mass was greatest on diets containing B. adusta, followed by T. versicolor, P. ostreatus, and F. pinicola. The growth rate of body mass correlated positively with mycelial nitrogen content of the different fungi. It also correlated positively with the mycelial content of B. adusta in the diet. Addition of antibiotics to diets with mycelia nearly halved larval growth, indicating that larvae were able to use fungal mycelia as food without the assistance of associated microbes although the microbes positively affected larval growth. Four newly hatched larvae reared on artificial diets containing B. adusta mycelia developed to the second instar in 21-34 days; and one developed to the third (=final) instar. This study provides evidence that fungi may constitute the bulk of the diet of D. rectus larvae.     

The essential dietary fatty acid requirement of the tufted apple budmoth, Platynota idaeusalis

The tufted apple budmoth, Platynota idaeusalis (Walker), was reared non-axenically for two successive generations on a casein-based semisynthetic diet. The qualitative essential fatty acid requirement for growth, development and normal pupal-adult ecdysis was studied using the non-axenic casein-based semisynthetic diets with and without various 99% pure fatty acids. Linoleic or linolenic acids caused accelerated larval development; linoleic, linolenic and arachidonic acids showed similar activity in body weight gain and survival to pupal-adult ecdysis. Linoleic or linolenic acids were active in alleviating wing deformities; arachidonic acid was partially active in alleviating wing deformities at the one dietary concentration evaluated. Activity of arachidonic acid as an essential fatty acid for P. idaeusalis is unique among insects, except for mosquitoes. The essential fatty acid deficiency syndrome of the adult, resulting from the larvae feeding on fat-deficient diets, was greatly reduced when larvae were fed on a diet adequate in essential fatty acid during either their early or late development.     

Effects of Temperature and Dietary Lipids on Phospholipid Fatty Acids and Membrane Fluidity in Steinernema carpocapsae

The phospholipid composition of Steinernema carpocapsae was studied in relation to diet and culture temperature. When reared at 18 and 27.5 C on Galleria mellonella or on an artificial diet supplemented with lard, linseed oil, or fish oil as lipid sources, nematode phospholipids contained an abundance of 20-carbon polyunsaturated fatty acids, with eicosapentaenoic acid (20:5(n - 3)) predominant, regardless of the fatty acid composition of the diet. Because the level of linolenic acid (18:3(n - 3)) in nematode phospholipids was very low and because eicosapentaenoic acid was present even when its precursor (linolenic acid) was undetectable in the diet, S. carpocapsae likely produces n - 3 polyunsaturated fatty acids by de novo biosynthesis, a pathway seldom reported in eukaryotic animals. Reduction of growth temperature from 25 to 18 C increased the proportion of 20:5(n - 3) but not other polyunsaturated fatty acids. A fluorescence polarization technique revealed that vesicles produced from phospholipids of nematodes reared at 18 C were less ordered than those from nematodes reared at 27.5 C, especially in the outermost region of the bilayer. Dietary fish oil increased fluidity in the outermost region but increased rigidity in deeper regions. Therefore, S. carpocapsae appears to modify its membrane physical state in response to temperature, and eicosapentaenoic acid may be involved in this response. The results also indicate that nematode membrane physical state can be modified dietarily, possibly to the benefit of host-finding or survival of S. carpocapsae at low temperatures.     

Ascorbic acid influence on larval blood cell number and susceptibility to bacterial and fungal infection in the codling moth, Laspeyresia pomonella (Lepidoptera: Tortricidae)

The optimum concentration of ascorbic acid in a semisynthetic diet for codling moth larvae was 0.6–0.8%. The number of circulating hemocytes and the percentage of prohemocytes and phagocytes decreased in larvae reared on the diet with suboptimal and supraoptimal ascorbic acid levels. These larvae were significantly more susceptible to Bacilus thuringiensis and Beauveria bassiana.     

Medetera aldrichii larval feeding behavior and prey consumption [Dipt.: Dolichopodidae]

Predatory behavior ofMedetera aldrichii Wheeler (Dolichopodidae) larvae was observed in bark-Lucite sandwiches infested with immature broods of the bark beetle preyDendroctonus pseudotsugae Hopkins (Scolytidae). Predator larvae could not penetrate unmined phloem or prey galleries tightly packed with frass, but moved through loose frass and bark-Lucite interspaces formed when the mined inner bark dried. At high prey densities interspace formation and gallerly contiguity enabled the predator to move freely and attack several prey in rapid succession. At low prey densities the predator was frequently isolated from prey by impenetrable strips of phloem. Predator larvae maintained singly in small plastic arenas consumed an average of 14.7 immature prey, but required only 6.2 prey when reared exclusively on large prey.     

Direct Effects of Microalgae and Protists on Herring (Clupea harengus) Yolk Sac Larvae

This study investigated effects of microalgae (Rhodomonas baltica) and heterotrophic protists (Oxyrrhis marina) on the daily growth, activity, condition and feeding success of Atlantic herring (Clupea harengus) larvae from hatch, through the end of the endogenous (yolk sac) period. Yolk sac larvae were reared in the presence and absence of microplankton and, each day, groups of larvae were provided access to copepods. Larvae reared with microalgae and protists exhibited precocious (2 days earlier) and ≥ 60% increased feeding incidence on copepods compared to larvae reared in only seawater (SW). In the absence and presence of microalgae and protists, life span and growth trajectories of yolk sac larvae were similar and digestive enzyme activity (trypsin) and nutritional condition (RNA-DNA ratio) markedly declined in all larvae directly after yolk sac depletion. Thus, microplankton promoted early feeding but was not sufficient to alter life span and growth during the yolk sac phase. Given the importance of early feeding, field programs should place greater emphasis on the protozooplankton-ichthyoplankton link to better understand match-mismatch dynamics and bottom-up drivers of year class success in marine fish.     

Nutritive effects of d-amino acids on the silkworm, Bombyx mori

Nutritive effects of d-amino acids on the silkworm, Bombyx mori, were investigated by growth experiments using defined diets and also by analysis of free amino acids in the larval haemolymph. None of the d-forms of the usual ten essential amino acids could be utilized effectively, although d-methionine was utilized in lieu of the l-form only to a limited extent and d-histidine gave a positive but smaller effect than d-methionine. d-Proline, its l-form being semi-essential for the silkworm, was not utilized. d-Leucine, and to a lesser extent d-alanine and d-serine, were found to be somewhat toxic. Comparison of free amino acid patterns in the haemolymph of the fifth-instar larvae, which fed on diets either lacking l-forms of histidine, methionine and leucine singly or including the d-forms singly in place of these l-forms, supported the results of the growth experiments.     

Performance of pine looper Bupalus piniarius larvae under population build-up conditions

In the first year of an outbreak, Bupalus piniarius larvae, encounter intense crowding. In the later stages of larval development, they are forced to feed on the non-preferred current-year needles of Scots pine or even on alternative hosts. It was hypothesized that larval feeding on a non-preferred resource (current-year needles) will negatively affect B. piniarius performance. It was also hypothesized that larval mutual interference (crowding without competition for food) will have negative additive effects. These hypotheses were tested in laboratory and field experiments. Fourth instar larvae were reared singly and under crowded conditions in cohorts of ten. Larvae in both situations were reared on control branches (containing both mature and current-year shoots) and branches containing only current-year shoots. Crowded larvae were reared also on Norway spruce, an alternative host. Crowding and feeding on a non-preferred resource had opposite effects on B. piniarius larval performance. Crowding in the late larval instars enhanced larval performance while absence of the preferred resource had negative effects. Larval growth rate was higher and development time was shorter for larvae exposed to crowded conditions than for solitary larvae. There was, however, no difference between the groups in final pupal weights or survival. Survival was 25% lower for larvae feeding on non-preferred current-year needles and pupal weights 9% lower, compared with results for larvae feeding on mature needles. Larvae feeding on Norway spruce suffered greatly extended development time, 82% lower survival, and resulted in 60% lighter pupae compared with conspecifics on Scots pine. It was concluded that not only quantity but also quality of the available food resource is critical for B. piniarius development.     

Diet-switching by gypsy moth: effects of diet nitrogen history vs. switching on growth, consumption, and food utilization

Gypsy moth (Lymantria dispar (L.) (Lepidoptera: Lymantriidae)) larvae were reared from hatch on 1.25% N or 3.5% N artificial diet (previous diet) and switched reciprocally to the other diet (current diet) after molting into the second, third, fourth, or fifth instar. The nitrogen concentration of food consumed during previous instars had a strong residual effect on the growth rate in subsequent instars when a diet switch was made during instars two through four, but did not affect growth rate of fifth-instar larvae despite effects on food consumption and utilization. In early instars, larvae reared on 1.25% N artificial diet and then switched to 3.75% N diet had lower mass-adjusted growth rates than larvae continuously reared on 3.75% N diet. Conversely, larvae reared on 3.75% N diet and switched to 1.25% N had higher mass-adjusted growth rates than larvae reared continuously on 1.25% N diet. Relative to larvae previously reared on 1.25% N diet, fifth-instar male larvae previously reared on 3.75% N diet had slightly lower consumption rates, higher net growth efficiency (ECD), and higher gross growth efficiency (ECI). Larvae previously reared on 3.75% N diet tended to have lower food assimilation efficiency (AD) and lower nitrogen assimilation efficiency (AD(N)). Although both previous and current diet nitrogen concentration strongly affected larval growth and food utilization, the interaction term between these was not significant for any response variables except ECD and ECI. Because the interaction term reflects the effect of switching per se, the results indicate that there was a metabolic cost associated with switching, but no inherent net cost or benefit of diet-switching to growth.     

Indirect plant-mediated effects on insect immunity and disease resistance in a tritrophic system

Host plant quality can significantly influence the growth and condition of phytophagous insects, and consequently their susceptibility to pathogens. This study examined the relationship between host plant quality, insect condition, immune responsiveness and resistance to pathogens in the cabbage looper, Trichoplusia ni. Two baseline and induced immune parameters were estimated, haemocyte numbers and haemolymph phenoloxidase (PO) activity, for larvae on two host plants, broccoli and cucumber. Haemolymph protein concentration was assessed as an indication of insect condition, and the susceptibility of larvae to T. ni single nucleopolyhedrovirus (SNPV) was used as a measure of disease resistance. T. ni growth, survival and condition was much higher on broccoli than cucumber. Haemocyte numbers were significantly higher in broccoli-reared larvae, whereas PO activity was not. An immune challenge induced significantly elevated numbers of haemocytes for larvae reared on both host plants, but did not affect PO activity or protein concentrations. Susceptibility to T. ni SNPV was markedly higher in larvae reared on cucumber than on broccoli. These results clearly indicate that host plant quality can affect both immune response and disease resistance of T. ni larvae and that bottom-up effects could be important in interactions between insects and entomopathogens.     

Anopheles stephensi and Toxorhynchites amboinensis: aseptic rearing of mosquito larvae on cultured cells

Aseptic larvae of Anopheles stephensi and Toxorhynchites amboinensis were reared on a continuous cell line (RU TAE 12 V) from the mosquito, T. amboinensis, that grew in suspension as multicellular vesicles. Surface-sterilized eggs were hatched in a 24-well plate containing 0.2 ml of Leibovitz's L-15 medium per well and incubated in a humidified atmosphere. Toxorhynchites amboinensis eggs of 36 hr or older were placed singly to assure hatching and avoid cannibalism. Hatching rates were over 80%. All larval instars were maintained in L-15 medium at 28 C with a 12-hr photoperiod. Anopheles stephensi larvae were reared in 25-cm2 tissue culture flasks containing 10 ml of L-15 medium with 30 to 50 first and second instar larvae or 10 third and fourth instar larvae per flask. Toxorhynchites amboinensis larvae remained in the 24-well plate in 1.5 ml of medium through the second instar; third instar larvae were kept in 12-well plates (3 ml of medium per well) and transferred to 25-cm2 flasks (10 ml per flask) when they reached the fourth instar. First and second instar A. stephensi larvae were fed cultured cells once, and third or fourth instar larvae twice a day. Toxorhynchites amboinensis larvae were fed vesicles once during the first 4 days after hatching, and every 1 or 2 days thereafter. Each A. stephensi larva consumed approximately 2 X 10(6) cells, and T. amboinensis larvae 10 times more cells before pupating. Anopheles stephensi pupated after 7 to 8 days and adults emerged during days 9 to 11. Pupation in T. amboinensis began on day 21 after hatching and adults emerged 5 days later. Cell lines isolated from A. stephensi larvae or embryos of the ticks Rhipicephalus sanguineus and Anocentor (Dermacentor) nitens supported only limited growth of A. stephensi larvae. Defibrinated hamster (Mesocricetus auratus) blood, though readily ingested, did not support the growth of A. stephensi whereas larvae reared on blood cells plus T. amboinensis cells showed limited growth.