Biogenic amines and phenolics characterize the defensive secretion of saturniid caterpillars (Lepidoptera: Saturniidae): a comparative study

The morphology of the scoli of Eudia pavonia, Saturnia pyri and Eupackardia calleta last instar caterpilars has been clarified. Chemical and biochemical comparisons of scolus secretions and corresponding caterpillar haemolymphs indicate two differing defensive strategies: Eudia and Saturnia contain phenolic and related compounds, whereas Eupackardia additionally synthesizes biogenic amines (e.g. neurotransmitters) in considerable amounts. For most aromatic compounds from the caterpillars a theoretical biogenetic scheme is proposed. Deterrent effects of all secretions and most haemolymphs on particular predatory ants were ascertained.Abbrevations CI chemical ionisation - EI electronimpact ionisation - GC-MS gas chromatography-mass spectrometry - GS gland secretion - HL haemolymph - PMSF phenylmethylsulphonyl fluoride - SDS-PAGF sodium dodecyl sulphate-polyacrylamide gel electrophoresis - SEM scanning electron microscope     

Foodplant preferences of Pieris caterpillars (Lepidoptera)

Summary Larvae of five Nearctic Pieris butterflies accept a wide range of native and naturalized crucifers under laboratory test conditions. Preferences among crucifers are usually statistical rather than absolute. Caterpillars do not necessarily reject plants that do not support larval growth in favor of those that do. Preferences are not significantly altered by larval development or prior experience with specific foodplant species. Progeny of different females do not exhibit significantly different preferences. Retention of behavioral flexibility by Pieris may enable older larvae to exploit alternative resources not suitable for young larvae.     

The "windows", scales, and bristles of the tropical moth Rothschildia lebeau (Lepidoptera: Saturniidae)

The common Spanish name of the moth Rothschildia lebeau (Saturniidae) is cuatro ventanas (four 'windows'), because it exhibits a transparent oval path in each wing. The scales of the colored areas and the bristles from the "window" were analyzed. We developed a simple device to measure transmittance across the "windows" with an spectrophotometer. A square section of "window" was mounted onto a flat black card and placed onto a clamp that hung in the path of the light - beam of the spectrophotometer. Absorbance was measured at 350 and 550 nm, with the "window" positioned perpendicular to the light beam (incidence of 90 degrees); then the measurements were repeated with the "window" moved at an angle of 45 degrees. Each measurement was replicated 5 times. Wing color spots were analyzed with a light dissection microscope (stereoscope) and with scanning electron microscopy. The scales have a minimum of 4 morphological types, 3 of them showed the typical appearance of unspecialized scales described for other butterflies; whereas the fourth has features particular to this species. On the "window" the scales are transformed in hair-like bristles that do not interfere with light, conferring the transparency that characterizes the "windows". However, if the wing is illuminated at an almost grazing-incidence, they reflect the light as a mirror. Two hypothetical functional explanation for the windows are mimicry and interspecies communication.     

Parasitism of orangestriped oakworm (Lepidoptera: Saturniidae) eggs in the urban landscape

Orangestriped oakworm, Anisota senatoria (J. E. Smith), has caused widespread defoliation of oak trees in the urban landscape of southeastern Virginia since 1985. Egg masses were collected from 1988 to 1990 to determine the impact of native egg parasites on A. senatoria populations. The most abundant egg parasite was Aprostocetus new sp. and mean egg mass parasitism was 24.6%. The eupelmid Anastatus hirtus (Ashmead), a new host record, parasitized a mean of 11.7% of A. senatoria egg masses. The encyrtid Ooencytrus sp., a new host record, had a mean egg mass parasitism of 0.09%. Inundative releases of Trichogramma minutum (Riley) in 1989 and 1990 did not increase parasitism rates and mean egg mass parasitism was 2.3%. Parasitism of first generation A. senatoria egg masses was higher compared with second generation. The four egg parasites collected in this study parasitized 30% of A. senatoria egg masses and within egg mass parasitism was 7.9%. These relatively low parasitism rates may partially explain the presence of consistently high A. senatoria populations in southeastern Virginia.     

Histopathology and ultrastructure of midgut of Alabama argillacea (Hübner) (Lepidoptera: Noctuidae) fed Bt-cotton

The interaction of Cry toxins from Bacillus thuringiensis in the midgut of some insect larvae determines their efficacies as insecticides, due to the expression and availability of sites of action of the toxin in the midgut. Researches point out cases of resistance to Cry toxin due to alterations in the binding sites in columnar cell membrane. We analyzed the effects of Cry1Ac toxin expressed by Bt-cotton plants on Alabama argillacea midgut morphophysiology clarifying in levels of morphological and ultrastructural. Larvae in the 4th instar of A. argillacea after 20 min from ingesting Bt-cotton leaves expressing 0.183 ng of Cry1Ac exhibited ultrastructural and morphological modifications in the columnar cells with significant changes in the mitochondrial polymorphism, cytoplasmic vacuolization, microvillus and basal labyrinth. Expressive morphological alterations were also observed in the goblet cells indicating that the columnar cells are not the only target of the Cry1Ac toxin. The regenerative cells did not modify their structures and exhibited decrease in regeneration capacity. In conclusion, the ingestion of 0.183 ± 0.077 ng of Cry1Ac was enough to promote alterations in the columnar and goblet cells, besides reducing significantly the number of regenerative cells, which may have contributed to larval death. Nevertheless, further studies are necessary to determine the true cause of death.     

Foodplant effects on colour morphs of Eumorpha fasciata caterpillars (Lepidoptera: Sphingidae)

Caterpillars of the hawkmoth Eumorpha fasciata are highly polymorphic for colour, with green, pink, and pink-and-yellow forms in the second through fourth instars, and green and multicoloured forms in the fifth instar. Four years of field censuses on four foodplant species determined that all morphs were found on all plant species; morph frequencies were homogeneous on each plant species over time; and morph frequencies differed consistently among plant species. When larvae were reared from eggs on three of the hostplant species in the laboratory, differences in morph frequencies paralleled the census results. Thus foodplant quality is one factor affecting larval colour in E. fasciata. A literature survey reveals that foodplant effects on larval colouration may be widespread in the family Sphingidae, but most reports are anecdotal rather than experimental. The implications of this mechanism of colour determination are discussed.     

New host-plant records for the defoliator Ormiscodes amphimone (Fabricius) (Lepidoptera: Saturniidae)

Ormiscodes amphimone (Fabricius) is a phytophagous moth species known to severely defoliate woody species in Chile and Argentina. Here we document new records of O. amphimonehost associations emphasizing the role of Nothofagus pumilio as its primary host in our study area. This new record for Argentina is highly significant given the economic importance of N. pumilio as a timber resource and the potential of O. amphimone to generate extensive outbreaks.     

Identification and characterization of a baculovirus from Lonomia obliqua (Lepidoptera: Saturniidae)

A baculovirus has been isolated from larvae of Lonomia obliqua, a Saturniidae of medical importance due to a potent toxin found in their spines. Electron Microscopy analysis of the occlusion body obtained from diseased larvae showed polyhedra of approximately 1 microm in diameter containing multiple nucleocapsids per envelope. This baculovirus was thus named Lonomia obliqua multicapsid nucleopolyhedrovirus (LoobMNPV). Restriction endonuclease profiles of viral DNA digested with three restriction enzymes were obtained and the genome size was estimated to be 95.52 +/- 2.3 kbp. The polyhedrin gene of LoobMNPV was identified and its DNA sequence was determined. Phylogenetic analysis of the polyhedrin gene showed that the LoobMNPV polyhedrin belongs to group I NPV and that it is closely related to the polyhedrin of the NPV of Amsacta albistriga.     

Direct and indirect effects of predatory wasps (Polistes sp.: Vespidae) on gregarious caterpillars (Hemileuca lucina: Saturniidae)

Summary We examined how predation by vespid wasps,Polistes dominulus andP. fuscatus, affected the behavior, growth rate and survivorship of aggregated caterpillars ofHemileuca lucina (Saturniidae). Although these larvae can exhibit a variety of defense and escape behaviors, in general larvae reacted to wasp attacks by clinging to the hostplant. Neighboring larvae in the aggregation responded by leaving the feeding site and moving to the interior or base of the plant. To determine wheter wasp attack affected the behavior and growth of the caterpillars that escaped, a field experiment was conducted with treatments of: 1) larvae exposed to wasps, 2) larvae protected from wasps, and 3) larvae protected from wasps but with the attack of wasps simulated (=harassment). Over just one instar, protected larvae gained significantly more weight than the harassed larvae, which in turn weighed significantly more than the larvae that escaped the wasps. The behavior of attacked and harassed larvae differed from that of the protected larvae; the disturbed larvae often fed in smaller groups and in shaded portions of the plant where only mature leaves were available. A laboratory experiment showed that at 35° C (daytime temperature) larvae had significantly higher relative growth rates and significantly shorter instar duration than larvae reared at 25° C. Our results suggest that wasps, in addition to killing caterpillars, indirectly affect larval fitness by slowing larval growth, at least in part by forcing larvae into cooler microhabitats where leaves are of lower quality.     

Winter predation of diapausing cocoons of slug caterpillars (Lepidoptera: Limacodidae)

Predators exert strong top-down pressure on herbivorous insects, but research on how predators affect herbivore fitness often focuses on the more active juvenile and adult life stages while ignoring the pupal or cocoon life stage. Few studies have investigated predation of lepidopteran pupae or cocoons and even fewer have investigated species that are not forest pests. Here we present a study on overwinter survival for two moth species in the family Limacodidae, a group of polyphagous species found in deciduous forests. We placed cocoons of the saddleback caterpillar, Acharia stimulea (Clemens), and the spiny oak-slug caterpillar, Euclea delphinii (Boisduval), in the field under saplings of six different tree species and monitored predation and survival. This is the first study to examine predation rate among different host plants within a site. We found that cocoon predation was fairly high and differed significantly between limacodid species (29% for A. stimulea vs. 22% for E. delphinii). Predation rate did not differ among the six host plant species that we tested and also did not vary annually. Through phenotypic selection analyses, we found that cocoon mass affected both the likelihood of predation and overwinter survival; larger cocoons were less likely to be depredated and more likely to successfully emerge the following year. Overall our results indicate that cocoon predation is an important source of mortality for these two limacodid species and that there may be positive selection for greater cocoon mass for both limacodid species.     

Effect of malathion and acetylcholine on the developing larvae ofPhilosamia ricini (Lepidoptera: Saturniidae)

Feeding of malathion induces accumulation of acetylcholine inPhilosamia ricini developing larvaevia inhibition of acetyl cholinesterase activity. The insecticide also causes depletion of all nutrients, loss in weight, under-development of silk glands resulting in reduced silk production, lack of oviposition and high mortality among the insects. Acetylcholine however, while fed during the same period of development, tones up their nutritional status, induces better growth, weight gain, improved silk production and oviposition and significantly lower mortality than in the control group of insects maintained on castor leaves. This improved status of insects has been attributed to choline, the insect vitamin released from acetylcholine. Acetylcholine has also been noted to protect the insects to some extent from the poisonous effect of malathion on exposure to it after a dose of acetylcholine during the preceding instar stadium     

Soldier bug predation on swallowtail caterpillars (Lepidoptera: Papilionidae): Circumvention of defensive chemistry

All larvae in the family Papilionidae possess osmeteria, eversible glands that release defensive chemicals upon disturbance. These chemicals have been shown to be repellent to ants, mantids, and other predaceous arthropods with chewing mouthparts. In this study, we demonstrate that the pentatomid Podisus maculiventris,an important predator of the black swallowtail Papilio polyxenes,is capable of piercing the body wall of the caterpillar and consuming body fluids without eliciting osmeterial eversion. Tenebrio molitorlarvae coated with osmeterial secretions of Papilio polyxeneswere universally rejected by Podisus maculiventris,suggesting that the predator is in fact repelled by the swallowtail defensive chemistry. By circumventing the defensive behavior of the caterpillar, the pentatomid is able to utilize an otherwise chemically unsuitable prey species.     

Impact of dietary allelochemicals on gypsy moth (Lymantria dispar) caterpillars: importance of midgut alkalinity

Midgut pH of gypsy moth larvae was depressed artificially with buffered diet to examine the impact of alkalinity on the caterpillars' ability to tolerate a dietary polyphenol and a quinone. A 2x3 factorial design was used, with 2 levels of succinate buffer and 3 dietary amendments (tannic acid, juglone, or control). Development was monitored during the third and fourth instars, with consumption, food passage rates, midgut pH, and midgut redox potential (Eh) measured in the fourth instar. Diet buffering successfully depressed midgut pH to hypothetically suboptimal acidic levels without reductions in survivorship, but it did reduce larval growth and impede development. Buffering dramatically reduced survivorship of fourth instar larvae eating diets containing tannic acid or juglone. Growth increased on unbuffered diet amended with tannic acid, but not with juglone. Caterpillars passed food through the gut more slowly when feeding on buffered tannic acid diet or on unbuffered juglone diet. These results indicate that maintenance of midgut alkalinity is critical to tolerance of dietary tannic acid and juglone, and that these allelochemicals have very different activities in the caterpillar gut.     

Assimilation efficiency of captive ringed seals (Phoca hispida) fed different diets

Food type or quality can influence assimilation efficiency (AE). AE (digestibility of dry matter) of two captive adult ringed seals (Phoca hispida; one male, one female) was estimated for five prey types. In trials, each of >8 days duration, the seals were fed redfish (Sebastes spp.), capelin (Mallotus villosus), Arctic cod (Boreogadus saida), Atlantic herring (Clupea harengus) and a mixture of herring and shrimp (Pandalus borealis). Prey were marked so that faecal samples could be matched to individual seals, and AE was estimated by the relative concentration of Mn²⁺ in food and faeces. AE was high but varied among the prey species (redfish 83%; capelin 87%; Arctic cod 88%; herring 94%; herring/Pandalus mixture 92%). There was a weak, positive relationship between AE and prey lipid content or energy density, but a negative relationship with inorganic content. AE was lower than expected for cape lin with high fat content. AE was not correlated with meal mass, number of fish in a meal, or seal mass. AE did not differ between the two seals. Received: 30 September 1996 / Accepted: 28 December 1996     

Egg ultrastructure in two Chilean moths: Ormiscodes socialis and Polythysana cinerascens (Lepidoptera: Saturniidae)

The structure and ultra-structure of the eggs from Ormiscodes socialis (Feisthamel) and Polythysana cinerascens (Philippi) are described, considering shape, size, coloring when recently laid, oviposition type and aeropiles (quantity, distribution and proportion) in the micropilar area, among others. The ultra-structure is shown for primary cells, secondary cells, aeropiles and micropiles. A comparative table of the eggs of these species is presented and includes the previously described eggs of Adetomeris microphthalma (Philippi). Myoschilos oblonga Ruiz y Pavón (Santalaceae) is recorded as a new host for P. cinerascens.     

Effects of larval diet on myrmecophilous qualities of Polyommatus icarus caterpillars (Lepidoptera: Lycaenidae)

Summary Fourth instar larvae of Polyommatus icarus maintain myrmecophilous associations with ants. In laboratory experiments, the attractiveness of larvae reared on foliage of the tree Robinia pseudacacia was significantly reduced compared with caterpillars fed with herbaceous Fabaceae. The ability to secrete carbohydraterich liquids from the dorsal nectary organ was also strongly reduced, while the function of the tentacle organs remained unaffected. The reductions in attractiveness and secretion abilities are caused by the food quality itself and not by secondary effects such as reduced larval size. The ecological significance of the results are discussed with respect to facultatively and obligately myrmecophilous lycacnids.