Effects of seven diets on the population dynamics of laboratory culturedTisbe holothuriae Humes (Copepoda,Harpacticoida)

The harpacticoid copepodTisbe holothuriae was collected from Saronicos Gulf (Greece) and reared under constant laboratory conditions. In order to study the effects of food on the population dynamics, seven diets were tested: the seaweedUlva; five artificial compound feeds: the liquid Fryfood^® (Waterlife), a powder ofMytilus, yeast, soya andSpirulina, respectively; and a mixed diet consisting ofUlva and Fryfood. The life cycle parameters (mortality, sex ratio, generation time, offspring production) were measured, and the demographic variables [mean generation time (T), net reproductive rate (Ro), and intrinsic rate of natural increase (r_m)] were determined. As to their efficiency regarding population dynamics, the diets ranked as follows: (1)Ulva+Fryfood, (2),Ulva, (3) Fryfood, (4)Mytilus, (5) soya, (6) yeast, and (7)Spirulina. In this order they cause a progressive increase of both larval mortality and generation time, a progressive decrease of sex ratio, number of offspring per egg sac, number of egg sacs per female and, consequently, of Ro and r_m. The observed differences between diets were most pronounced with respect to offspring production. Of the compound diets, those containing animal extracts were more efficient than those containing vegetable materials.Ulva plays an important role in the nutrition ofT. holothuriae, favouring offspring production as well as larval survival, development and pigmentation.Ulva in combination with Fryfood led to a greater copepodid survival and offspring production. This mixed diet proved to be the most favourable for rearing the Greek population oft. holothuriae, resulting in an efficient intrinsic rate of natural increase (r_m=0.304) of the population.     

Invertebrate biodiversity affects predator fitness and hence potential to control pests in crops

Natural enemies that control pests usually allow farmers to avoid, or reduce, the use of pesticides. However, modern farming practices, that maximize yields, are resulting in loss of biodiversity, particularly prey diversity. Does this matter? Pests continue to thrive, and without alternative prey the predators should, perforce, concentrate their attentions upon the pests.We showed that a diverse diet significantly enhances predator fecundity and survival. Experiments were conducted using common generalist predators found in arable fields in Europe, the carabid beetle Pterostichus melanarius (Coleoptera: Carabidae) and the linyphiid spider Erigone atra (Araneae: Linyphiidae). We tested the hypothesis that mixed species diets were optimal, compared with restricted diets, with respect to parameters such as predator weights, egg weights, numbers of eggs laid, egg development times, egg hatching rates and predator survival. In carabids, an exclusive earthworm diet was as good as mixed diets containing earthworms for egg production and hatching, but less good than such mixed diets for increase in beetle mass and sustained egg laying. For spiders, aphids alone (Sitobion avenae) or with the Collembola Folsomia candida, drastically reduced survival. Aphids plus the Collembola Isotoma anglicana improved survival but only aphids with a mixed Collembola diet maximized numbers of hatching eggs.Predators offered only pests (slugs or aphids) had lowest growth rates and fecundity. We therefore demonstrated that conservation of a diversity of prey species within farmland, allowing predators to exploit a diverse diet, is essential if predators are to continue to thrive in crops and regulate agricultural pests.     

Two Meridic Diets for Perillus bioculatus (Heteroptera: Pentatomidae), a Predator of Leptinotarsa decemlineata (Coleoptera: Chrysomelidae)

Two artificial diets, devoid of insect components, were developed for the predator Perillus bioculatus (Fabricius). The diets based on chicken liver and tuna fish were designed to approach the nutritional characteristics of the primary insect prey, Leptinotarsa decemlineata (Say) eggs. P. bioculatus was reared on diet 2 for 11 consecutive generations without cumulative detrimental effects on its biology. Developmental time and preovipositional period were significantly longer, and egg viability, survival from egg to adult, and fecundity were significantly lower in P. bioculatus individuals reared on artificial diets than in those reared on L. decemlineata eggs. A significant reduction in developmental time, increase in survival from egg to adult, and reduction in length of the preovipositional period were observed after 11 generations of in vitro reared P. bioculatus on diet 2. These changes may indicate that the predators experience some degree of adaptation to the diet after several consecutive generations of in vitro rearing. No changes in egg viability were observed after 11 generations of in vitro rearing. Adult female weight was unaffected when reared on artificial diet, but a significant increase was observed after 11 generations of in vitro rearing. Females under all treatments weighed an average of 11.6 mg more than the males.     

Food quality of Ephestia eggs,the aphid Rhopalosiphum padi and mixed diet for Orius majusculus

We studied the food quality of the aphid Rhopalosiphum padi to the pirate bug Orius majusculus using Ephestia eggs as high-quality comparison prey. Several performance parameters were tested on individuals that had been reared and maintained on each of the two single-prey diets or on a mixed diet. All fitness parameters were lower in individuals fed aphids only, indicating poor food quality of this prey. Compared with the pure Ephestia egg diet, the mixed diet enhanced teneral mass, while adult survival and female starvation tolerance were negatively affected and all other traits were unaffected. Body protein proportions were constant across diets, whereas lipid proportion was low in the aphid treatment. Preference for aphids was lower following a monotypic aphid diet than when reared on Ephestia eggs or a mixed diet. The results confirm that R. padi is low-quality food for O. majusculus as it is for other generalist predators, even though O. majusculus may contribute significantly to population suppression of the aphid.     

Copepod Foraging on the Basis of Food Nutritional Quality: Can Copepods Really Choose?

Copepods have been considered capable of selective feeding based on several factors (i.e., prey size, toxicity, and motility). However, their selective feeding behaviour as a function of food quality remains poorly understood, despite the potential impact of such a process on copepod fitness and trophodynamics. In this study, we aimed to evaluate the ability of copepods to feed selectively according to the nutritional value of the prey. We investigated the feeding performance of the calanoid copepod Acartia grani under nutritionally distinct diets of the dinoflagellate Heterocapsa sp. (nutrient-replete, N-depleted and P-depleted) using unialgal suspensions and mixtures of prey (nutrient-replete vs. nutrient-depleted). Despite the distinct cell elemental composition among algal treatments (e.g., C:N:P molar ratios) and the clear dietary impact on egg production rates (generally higher number of eggs under a nutrient-replete diet), no impact on copepod feeding rates was observed. All unialgal suspensions were cleared at similar rates, and this pattern was independent of food concentration. When the prey were offered as mixtures, we did not detect selective behaviour in either the N-limitation (nutrient-replete vs. N-depleted Heterocapsa cells) or P-limitation (nutrient-replete vs. P-depleted Heterocapsa cells) experiments. The lack of selectivity observed in the current study contrasts with previous observations, in which stronger nutritional differences were tested. Under normal natural circumstances, nutritional differences in natural prey assemblages might not be sufficiently strong to trigger a selective response in copepods based on that factor alone. In addition, our results suggest that nutritional quality might depend not only on the growing conditions but also on the inherent taxonomical properties of the prey.     

Effect of diet and mating status on ovarian development and oviposition in the polyphagous predator Macrolophus caliginosus (Heteroptera: Miridae)

The mirid bug Macrolophus caliginosus is commercially reared on eggs of Ephestia kuehniella, constituting an effective but expensive factitious food. Artificial diets can decrease the rearing costs of this natural enemy, but developing and evaluating an artificial diet is a very time-consuming activity. In the current study, development and reproduction of M. caliginosus on two artificial diets based on egg yolk were investigated. The artificial diets resulted in longer development and lower adult weights, but survival was comparable with that of control insects fed E. kuehniella eggs. Reproductive potential of the predator reared on factitious and artificial foods was assessed using a dissection method. The influence of nymphal food on fecundity was less important than that of adult food. Adults fed E. kuehniella eggs had a preoviposition period of about 4 days, whereas adults offered only plant material started laying eggs about 7 days after emergence. Ovarian scores at day 7 were higher for females fed E. kuehniella eggs than for those given access only to a tobacco leaf. Ovarian scores were not significantly affected by mating status. In a final test, a parallel comparison of two methods for assessing reproductive response to diet was made. Here, adult couples were offered one of four diets: E. kuehniella eggs, one of two artificial diets or no food. Half of the females were dissected and the other half was held for determining lifetime oviposition. Females fed E. kuehniella eggs had superior ovarian scores and laid more eggs than those fed either artificial diet or those given no extra food. A good correlation (r = 0.97) was obtained between ovarian scores and oviposition data, indicating that dissecting females after 1 week provides a reliable estimate of fecundity as affected by diet quality. Rapid reproductive assessments as used in the current study will help to increase the rate of development of artificial diets and may contribute to more cost effective production methods for augmentative biological control agents.     

Viability of dinoflagellate cysts after the passage through the copepod gut

Several dinoflagellate species form nonmotile, thick-walled resting cysts in their life cycle. Cysts can be ingested by planktonic and benthic organisms, but there is scarce information concerning their survival after the passage through the digestive apparatus of the grazers. We tested the germination capability of cysts produced by two neritic dinoflagellates, Scrippsiella trochoidea (F. Stein) A.R. Loeblich and Scrippsiella ramonii Montresor, after their ingestion by four copepod species. Experiments have been carried out with four species: Acartia clausi Giesbrecht, 1889; Centropages typicus Kröyer, 1849; Temora stylifera Dana, 1849; and Clausocalanus lividus Frost and Fleminger, 1968. Copepods were fed either with motile cells or cysts, and feeding and clearance rates were estimated for A. clausi, C. lividus and T. stylifera. Grazing rates on both dinoflagellates was much higher for vegetative cells than for cysts. Resting cysts were isolated from the faecal pellets and incubated to test their germination capability. S. trochoidea cysts eaten by C. typicus and T. stylifera showed a high germination rate, while cysts of the same species were not viable after the passage through the gut of A. clausi and C. lividus. In contrast, S. ramonii cysts were never able to germinate after being ingested by copepods. The observed variation in viability among the two cyst types and the different survival rates observed for S. trochoidea cysts might be related to differences in cyst morphology and to differences in the digestive process among the tested copepod species.     

Are the diatoms Navicula sp. and Thalassiosira fluviatilis suitable to be fed to the benthic harpacticoid copepod Tisbe biminiensis?

The objective of this study was to compare the influence of the diets of two diatoms, Navicula sp. (benthic) and Thalassiosira fluviatilis (planctonic), on the development, fecundity and survival of the harpacticoid copepod Tisbe biminiensis. In order to determine the optimal concentration of food, 35 egg-bearing females were submitted to six algal concentrations and controls (without food). After 24 h, the content of the recipients was fixed with 4% formalin and then fecal pellets produced by each female were counted and measured. The larval development was studied by surveying 50 nauplii on each diet individually until the adult stage, at intervals of 6 h. The cast exoskeletons were removed to count the number of segments and for measurement. The fecundity was obtained counting the naupliar production every 48 h of groups containing 10 females in different algal concentrations in both diets. The diet influence on fecundity was tested by submitting four groups of 10 females fed on optimal algal concentrations based on the fecal pellet experiments. In the Navicula sp. concentration of 0.4 μg Chl-a/ml, considered to be optimal for fecal pellets production, the diatoms were shown toxic, resulting in a low survival rate and inhibiting the egg production of copepods. The optimal concentration considering fecundity was estimated to be 0.1 μg Chl-a/ml for both diets. Copepods fed on Navicula sp. presented a faster development rate and higher naupliar production compared to copepods fed on T. fluviatilis. Size and survival did not vary significantly among diets. The algal concentration interfered significantly in the reproductive success of females. Both very low and very high algal concentrations reduced reproductive success. Concluding, the benthic diatom Navicula sp. was more favorable to the copepod T. biminiensis than the planktonic diatom T. fluviatilis.     

Omnivory in the calanoid copepod Temora longicornis: feeding, egg production and egg hatching rates

We measured in laboratory experiments the ingestion, egg production and egg hatching rates of female Temora longicornis as a function of diet. The diets consisted of a diatom (Thalassiosira weissflogii), an autotrophic dinoflagellate (Heterocapsa triquetra), and a bacterivorous ciliate (Uronema sp.) given as sole foods, or combinations of these single-food items: diatom+dinoflagellate, diatom+ciliate, dinoflagellate+ciliate, and diatom+ciliate+dinoflagellate. For the three single-item diets, the functional response was similar; i.e., ingestion rate increased linearly with food concentration (food range: ∼25 to ∼600 μg C l⁻¹). When all diets were considered, maximum daily carbon ration (∼70% of body weight) was independent of food type. However, the maximum daily egg production rate (12% of body carbon) was obtained with the diatom diet. For all diets, both ingestion and egg production rates increased with food concentration. Ingestion and egg production rates were affected differently by the interaction of food concentration and food type: at low food concentrations, ingestion rates were highest on diets containing the diatom. At high food concentrations, egg production rates were highest on the two phytoplankter diets and their combination. The presence of the ciliate in the diet did not enhance ingestion rate or egg production. Mixed-food diets did not enhance egg production relative to single-food diets. Hence, dietary diversity did not appear to be particularly advantageous for reproduction. Carbon-specific egg production efficiency (EPE; egg production/ingestion) was independent of food concentration and type, and equaled 9%. Egg hatching success was low (mean<30%) and independent of food concentration and type, and egg production rates. Our results are consistent with previous observations that egg production in T. longicornis is enhanced during diatom blooms. However, the relatively low EPE and egg hatching success suggest that reproduction and recruitment in this study were severely constrained by the biochemical composition of the diet, or the physiological condition of the females towards the end of their season of growth in Long Island Sound.     

Fitness consequences for copepods feeding on a red tide dinoflagellate: deciphering the effects of nutritional value, toxicity, and feeding behavior

Phytoplankton exhibit a diversity of morphologies, nutritional values, and potential chemical defenses that could affect the feeding and fitness of zooplankton consumers. However, how phytoplankton traits shape plant–herbivore interactions in the marine plankton is not as well understood as for terrestrial or marine macrophytes and their grazers. The occurrence of blooms of marine dinoflagellates such as Karenia brevis suggests that, for uncertain reasons, grazers are unable to capitalize on, or control, this phytoplankton growth—making these systems appealing for testing mechanisms of grazing deterrence. Using the sympatric copepod Acartia tonsa, we conducted a mixed diet feeding experiment to test whether K. brevis is beneficial, toxic, nutritionally inadequate, or behaviorally rejected as food relative to the palatable and nutritionally adequate phytoplankter Rhodomonas lens. On diets rich in K. brevis, copepods experienced decreased survivorship and decreased egg production per female, but the percentage of eggs that hatched was unaffected. Although copepods showed a 6–17% preference for R. lens over K. brevis on some mixed diets, overall high ingestion rates eliminated the possibility that reduced copepod fitness was caused by copepods avoiding K. brevis, leaving nutritional inadequacy and toxicity as remaining hypotheses. Because egg production was dependent on the amount of R. lens consumed regardless of the amount of K. brevis eaten, there was no evidence that fitness costs were caused by K. brevis toxicity. Copepods limited to K. brevis ate 480% as much as those fed only R. lens, suggesting that copepods attempted to compensate for low food quality with increased quantity ingested. Our results indicate that K. brevis is a poor food for A. tonsa, probably due to nutritional inadequacy rather than toxicity, which could affect bloom dynamics in the Gulf of Mexico where these species co-occur.     

Maternal and neonate diatom diets impair development and sex differentiation in the copepod Temora stylifera

Development and sex differentiation in the copepod Temora stylifera was studied in the presence of maternal and larval diets of the diatoms Thalassiosira rotula and Skeletonema marinoi, either provided alone or supplemented with the control dinoflagellate Prorocentrum minimum. Both diatoms had deleterious effects on growth compared to the control when used as pure diets, inducing very low or even zero survival from hatching to adulthood. This effect was deleted when the diet was supplemented with a good food (P. minimum) only in the case of T. rotula. By contrast, with a maternal or larval diet of S. marinoi, nauplii did not pass metamorphosis even when this alga was mixed with P. minimum. Arrested development was not due to lack of feeding since early and late nauplii (NII and NV) ingested all three algae at similar rates when used as single diets, and did not show any preference when the algae were offered as mixtures. Since mortality rates with a mixed diet of S. marinoi + P. minimum were similar or even higher than those obtained with a single diet of S. marinoi, we suggest that this diatom is more toxic than nutritionally deficient for T. stlyfera development. No males were produced in cohorts reared on pure diatom diets or with a mixture of S. marinoi + P. minimum, and intermediate male:female sex ratios were obtained with the mixed T. rotula + P. minimum diet. Possibly some diatoms produce compounds such as oxylipins or new molecules that alter sex differentiation in T. stylifera.     

Invertebrate biodiversity affects predator fitness and hence potential to control pests in crops

Natural enemies that control pests usually allow farmers to avoid, or reduce, the use of pesticides. However, modern farming practices, that maximize yields, are resulting in loss of biodiversity, particularly prey diversity. Does this matter? Pests continue to thrive, and without alternative prey the predators should, perforce, concentrate their attentions upon the pests.We showed that a diverse diet significantly enhances predator fecundity and survival. Experiments were conducted using common generalist predators found in arable fields in Europe, the carabid beetle Pterostichus melanarius (Coleoptera: Carabidae) and the linyphiid spider Erigone atra (Araneae: Linyphiidae). We tested the hypothesis that mixed species diets were optimal, compared with restricted diets, with respect to parameters such as predator weights, egg weights, numbers of eggs laid, egg development times, egg hatching rates and predator survival. In carabids, an exclusive earthworm diet was as good as mixed diets containing earthworms for egg production and hatching, but less good than such mixed diets for increase in beetle mass and sustained egg laying. For spiders, aphids alone (Sitobion avenae) or with the Collembola Folsomia candida, drastically reduced survival. Aphids plus the Collembola Isotoma anglicana improved survival but only aphids with a mixed Collembola diet maximized numbers of hatching eggs.Predators offered only pests (slugs or aphids) had lowest growth rates and fecundity. We therefore demonstrated that conservation of a diversity of prey species within farmland, allowing predators to exploit a diverse diet, is essential if predators are to continue to thrive in crops and regulate agricultural pests.     

Relationship between functional response and gut transit time in the calanoid copepod Acartia clausi: role of food quantity and quality

The relationship between ingestion rate and gut transit timeof the calanoid copepod Acartia clausi was examined in laboratoryexperiments with five different diets: (i) living cells of thediatom Thalassiosira weissflogii, (ii) detrital cells of thesame diatom, (iii) 50:50 mix of the two previous diets on aprotein basis, (iv) dinoflagellate cells of Prorocentrum micansand (v) Prorocentrum minimum. Ingestion followed a Holling type2 response for diets 1 and 4 and a linear one for diets 2, 3and 5. Gut transit time varied with food abundance only whenthe copepods were fed with the living diatom. The gut evacuationrate increased with the concentration of T. weissflogii withvalues of 0.010, 0.020, 0.032, 0.042 min^–1, correspondingto gut transit time of 97, 50, 31 and 24 min, measured at 50,110, 130 and 275 µg protein L^–1, respectively. Copepodsfed with dinoflagellates, mixed and pure detrital diets exhibitedlonger and similar gut transit times ranging from 85 to 166min, depending on diet. The coupling between ingestion rateand gut transit time measurements is discussed in the contextof copepod feeding strategies.     

Cyst production in four species of neritic dinoflagellates

The production of resting cysts in four species of dinoflagellates(Scrippsiella trochoidea, Ensiculifera sp., Alexandrium lusitanicumand Lingulodinium polyedra) was studied in response to severalenvironmental factors of ecological importance (nitrate, phosphate,iron, copper and cyanocobalamin deficiencies, high concentrationsof copper, turbulence, darkness plus concentration. as wellas various media biologically conditioned by dinoflagellates)using unialgal cultures and enrichments of natural populations.Some nutritional deficiencies, mainly phosphorus or nitrogen(in this order), are the most effective inducers of encystment.Among the other deficiencies tested, only iron deficiency wasimportant, affecting only A.lusitanicum. In some cases, biologicalconditioning produced considerable encystment reductions, makingit an important means of competition between species. We suggestthat encystment may be induced in these neritic species by deficienciesin compounds that act as indicators of changes in the hydrographicconditions to which the particular species are adapted.     

The effects of a microcystin-producing and lacking strain of Microcystis on the survival of a widespread tropical copepod (Notodiaptomus iheringi)

The tropical copepod Notodiaptomus iheringi (N. iheringi) is an ideal subject for studying zooplankton responses to cyanobacteria because it co-exists with permanent blooms across widespread regions in South America in high abundance. Single and mixed diets containing Cryptomonas and either a microcystin-producing (MC+) or microcystin-lacking (MC?) Microcystis were offered to N. iheringi at different proportions in a 10-day laboratory survival test to distinguish between the effects of toxicity versus nutrition. As expected, the pure MC+ Microcystis diet caused acute toxicity, indicated by high mortality compared to starved copepods. Both Microcystis strains were ingested in a 3-h short-term grazing experiment with pure diets. Despite its toxicity as the sole food source, survival was unaffected by MC+ Microcystis in mixed food diets. Even when MC+ Microcystis was 90% of the total food, survival was similar to the control with 10% Cryptomonas only. Hence, the survival in mixed food diets was controlled by the amount of Cryptomonas, not Microcystis. Previous reports show strong negative effects of Microcystis on copepod survival despite abundant high-quality food. Although this is the first example of copepods avoiding acute Microcystis toxicity in mixed diets, it could be a common trait where permanent blooms dominate the ecosystem.     

Genetic variability in growth rates of marine dinoflagellates

The growth rates of thirty clones of Prorocentrum micans, twenty-two clones of Gonyaulax excavata and fifteen clones of Scrippsiella trochoidea, isolated from eight different water samples were measured under two environmental conditions. There was significant genetic variability in growth rates between clones. The amount of genetic variability between clones ranged from 10–27% (coefficient of variation) in Prorocentrum micans, 31–52% in Gonyaulax excavata and 11–20% in Scrippsiella trochoidea. Unlike Gonyaulax excavata and Scrippsiella trochoidea many different Prorocentrum micans clones had identical growth rates.Supported by Spanish CAICYT, grant num. 2409/83.     

Effect of diet and mating status on ovarian development and oviposition in the polyphagous predator Macrolophus caliginosus (Heteroptera: Miridae)

The mirid bug Macrolophus caliginosus is commercially reared on eggs of Ephestia kuehniella, constituting an effective but expensive factitious food. Artificial diets can decrease the rearing costs of this natural enemy, but developing and evaluating an artificial diet is a very time-consuming activity. In the current study, development and reproduction of M. caliginosus on two artificial diets based on egg yolk were investigated. The artificial diets resulted in longer development and lower adult weights, but survival was comparable with that of control insects fed E. kuehniella eggs. Reproductive potential of the predator reared on factitious and artificial foods was assessed using a dissection method. The influence of nymphal food on fecundity was less important than that of adult food. Adults fed E. kuehniella eggs had a preoviposition period of about 4 days, whereas adults offered only plant material started laying eggs about 7 days after emergence. Ovarian scores at day 7 were higher for females fed E. kuehniella eggs than for those given access only to a tobacco leaf. Ovarian scores were not significantly affected by mating status. In a final test, a parallel comparison of two methods for assessing reproductive response to diet was made. Here, adult couples were offered one of four diets: E. kuehniella eggs, one of two artificial diets or no food. Half of the females were dissected and the other half was held for determining lifetime oviposition. Females fed E. kuehniella eggs had superior ovarian scores and laid more eggs than those fed either artificial diet or those given no extra food. A good correlation (r = 0.97) was obtained between ovarian scores and oviposition data, indicating that dissecting females after 1 week provides a reliable estimate of fecundity as affected by diet quality. Rapid reproductive assessments as used in the current study will help to increase the rate of development of artificial diets and may contribute to more cost effective production methods for augmentative biological control agents.     

Growth of Nyctiphanes (Euphausiacea) on different diets

To determine the effects of diet on the growth rate of Nyctiphanes australis (Euphausiacea), metanauplii were reared to mature adults in the laboratory. Sibships (siblings from the same mother) were raised on different food items collected from the field and cultured in the laboratory. A sibship was divided at the calyptopis stage and 50% of the siblings were fed one of three experimental diets (Thalassiosira, Heterocapsa, or Phaeocystis); the balance of the siblings were fed a control diet of Tetraselmis chuii and Artemia larvae.The growth rate of siblings was not altered by the different diets. Siblings developed asynchronously, however, from egg to adult.Some animals were always at a more advanced developmental phase and by day 100, up to 25% larger than their siblings (p<0.001). A possible implication of this result is that the larval growth of N. australis is strongly influenced by genotype.     

Artificial diets for rearing the coconut hispine beetle Brontispa longissima and its parasitoid Asecodes hispinarum

We tested artificial diets for rearing the coconut hispine beetle, Brontispa longissima, a serious invasive pest of coconut (Cocos nucifera) in Southeast Asia. We examined three artificial diets that were identical except for their agar content. The survival rate from hatching to adult emergence was 26.0% when beetles were reared on a ‘soft diet’ (20 g/l agar), 16.0% on a ‘hard diet’ (40 g/l agar), and 41.0% on a ‘mixed diet’, in which the hard diet was used for the first instar and the soft diet for later instars. Females raised as larvae on the mixed diet and then as adults on the soft diet laid few eggs, which did not hatch. However, females reared on the mixed diet as larvae and then on fresh leaves as adults consistently laid eggs that hatched. We then examined the suitability of B. longissima larvae reared on the mixed diet as hosts for the larval parasitoid Asecodes hispinarum, a specialist parasitoid of this beetle. Of the oviposited hosts, 75.0% became mummified and 41.7% produced adult wasps. These results indicate that the mixed diet may be useful for rearing B. longissima larvae as hosts for the rearing of A. hispinarum.     

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.