Effect of desalination on the littoral tecturid gastropods in early development

The effect of decreased salinity on the limpetsCollisella dorsuosa, C. versicolor, C. radiata, andNotoacmea concinna (Mollusca, Gastropoda) is studied at early stages of development. It is shown that, for normal development from fertilization to the veliger stage, the salinity must be not less than 22–24‰. A decrease in salinity depressed the behavior of larvae. At earlier stages, the larvae were less sensitive to changes in salinity than at later stages. At the same time, veligers were better able to adapt to changes in salinity than trochophores. The vertical water distribution of larvae depended on their age. Two days after fertilization, the larvae sank down to start a benthic life. It is proposed that the narrow tolerance range of littoral limpet larvae to changes in salinity is connected with the fact that they spend a relatively small part of their life in plankton.     

Local epizootics caused by teleomorphic cordycipitoid fungi (<Emphasis Type=Italic>Ascomycota: Hypocreales</Emphasis>) in populations of forest lepidopterans and sawflies of the summer-autumn complex in Siberia

Unique epizootic loci were revealed in the summer-autumn complex of the multispecies communities of forest lepidopterans and sawflies in two regions of Novosibirsk oblast and in the Baikal region at the border of the Buryat Republic and Irkutsk oblast. Mass insect mortality was caused by two species of cordycipitoid fungi: Cordyceps militaris and Cordyceps sp. At least 30 species from 7 families of millers (Macroheterocera) and sawflies from the family Cimbicidae were found to be C. militaris hosts. Lepidopterans from the family Thyatiridae are the hosts of the second species, Cordyceps sp. Total mortality was noted for the condition close to optimal for pupation, i.e., in places of mass pupa accumulation. It may be assumed on the basis of the results of the laboratory experiments that, under natural conditions, host insects may be infected by ascospores and conidia at the anamorphic stage.     

An increase in the immune system activity of the wax moth Galleria mellonella and of the Colorado potato beetle Leptinotarsa decemlineata under effect of organophosphorus insecticide

Several aspects of immune response in insects treated with an organophosphate (pirimiphosmethyl) have been assessed. Both humoral (phenoloxidase activity) and cellular (hemocyte count and encapsulation rate) immunity changes have been studied in larvae of the representatives of two insect orders, the Colorado potato beetle Leptinotarsa decemlineata (Coleoptera, Chrysomelidae) and the wax moth Galleria mellonella (Lepidoptera, Pyralidae). A direct contact with sublethal and half-lethal doses of the insecticide results in stimulation of immune reactions: phenoloxidase activity and encapsulation rate are heightened, and hemocyte count increases.     

Phenotypic variability of environmental isolates of the entomopathogenic fungus <Emphasis Type="Italic">Beauveria bassiana</Emphasis>

A total of 35 isolates of Beauveria bassiana (Bals.) Vuill. isolates obtained from various insects of Novosibirsk oblast were investigated. The fungal morphotypes were found to include cultures of high, medium, and low virulence. Low correlation (r < 0.48) was observed between virulence and the morphophysiological characteristics of the isolates (lipase and protease activity, biomass, radial growth rate, conidia productivity, and relief). Isolates exhibiting high virulence to insects of a certain order proved to be virulent to the insects of other orders. A high correlation (r > 0. 74) was revealed between the virulence of the isolates to the potato beetle Leptinotarsa decemlineata Say and the locusts Calliptamus barbarus Costa and Locusta migratoria L. Isolates obtained from insects of the same species in the same site may differ significantly in virulence.     

Effect of temperature on early development of the Pacific mussel <Emphasis Type="Italic">Mytilus trossulus</Emphasis> (Bivalvia: Mytilidae) in sea water polluted by copper ions

The effects of water temperatures of 7, 15 and 20°C and pollution of sea water by copper ions in concentrations of 0.005 and 0.01 mg/l on the early development of the Pacific mussel Mytilus trossulus were studied. It was shown that copper additives were most toxic at the initial stages of development, from fertilization up to the veliger stage. It was determined that larvae of the Pacific mussel were able to adapt to copper at a concentration of 0.005 mg/l. The copper toxicity increased to a greater extent with an increase in water temperature from its average value of 15°C, than with a temperature decrease.     

Protection of Embryos from Freshening and Drying in Layings of the Gastropod Littorina sitkana

Protection from wetting (freshening) and drying of layers of the intertidal gastropod Littorina sitkana Philippi, 1846, specified by direct development was studied. It has been shown that the jellylike material of the layings did not protect the developing embryos from changes in the environmental salinity, but rather protected them from drying periods up to 12 h.     

The Vertical Distribution of Larvae of the Sea Urchin Strongylocentrotus intermedius in Superficial Desalination Conditions

The vertical distribution of larvae of the sea urchin Strongylocentrotus intermedius in conditions of superficial desalination was studied under laboratory conditions. In the earlier stages of development, the larvae accumulated in the water column zone with a salinity below the optimal level. The long-term observations of the larval accumulations revealed the deceleration of, and abnormalities in, the development and death of the larvae. The larvae at the pre-settling stages changed their behavior: when they reached layers of a salinity unfavorable for their survival or development, the larvae did not enter them and instead moved down instead. Obviously, S. intermedius larvae are only capable of actively choosing their position within the water column with the salinity gradient at the later stages of development.     

Comparative analysis of immune responses in Colorado potato beetle larvae during development of mycoses caused by <Emphasis Type="Italic">Metarhizium robertsii</Emphasis>, <Emphasis Type="Italic">M. brunneum</Emphasis>, and <Emphasis Type="Italic">M. pemphigi</Emphasis>

Development of mycoses and progress of humoral and cellular immune responses were compared in larvae of the Colorado potato beetle Leptinotarsa decemlineata infected with entomopathogenic fungi Metarhizium robertsii, M. brunneum and M. pemphigi. The larvae were found to be highly susceptible to the strains of M. robertsii and M. brunneum but weakly responsive to M. pemphigi. The extent of susceptibility to the pathogens was not related to the stimulating effect of epicuticular extracts on fungal growth. Metarhizium pemphigi, which is non-specific to the Colorado potato beetle, did not cause any significant changes in the immune response and did not colonize the hemocoel. When infected with M. robertsii and M. brunneum, the larvae exhibited an increase in hemocyte count during the early stage of mycosis (day 2) followed by a drastic decrease on day 3. The immunocompetent cells, plasmatocytes and granulocytes, exhibited the greatest decrease. Elevated phenoloxidase activity was recorded in the hemolymph and cuticle on days 2 and 3 post-infection. These changes in the immune responses correlated with strain-specific virulence. Thus, the immune response in Colorado potato beetle larvae is an important factor, which determines differences in the development of mycoses caused by different Metarhizium species.     

More than a colour change: insect melanism,disease resistance and fecundity

A ‘dark morph’ melanic strain of the greater wax moth, Galleria mellonella, was studied for its atypical, heightened resistance to infection with the entomopathogenic fungus, Beauveria bassiana. We show that these insects exhibit multiple intraspecific immunity and physiological traits that distinguish them from a non-melanic, fungus-susceptible morph. The melanic and non-melanic morphs were geographical variants that had evolved different, independent defence strategies. Melanic morphs exhibit a thickened cuticle, higher basal expression of immunity- and stress-management-related genes, higher numbers of circulating haemocytes, upregulated cuticle phenoloxidase (PO) activity concomitant with conidial invasion, and an enhanced capacity to encapsulate fungal particles. These insects prioritize specific augmentations to those frontline defences that are most likely to encounter invading pathogens or to sustain damage. Other immune responses that target late-stage infection, such as haemolymph lysozyme and PO activities, do not contribute to fungal tolerance. The net effect is increased larval survival times, retarded cuticular fungal penetration and a lower propensity to develop haemolymph infections when challenged naturally (topically) and by injection. In the absence of fungal infection, however, the heavy defence investments made by melanic insects result in a lower biomass, decreased longevity and lower fecundity in comparison with their non-melanic counterparts. Although melanism is clearly correlated with increased fungal resistance, the costly mechanisms enabling this protective trait constitute more than just a colour change.     

Combined action of the entomopathogenic fungus <Emphasis Type="Italic">Metarhizium robertsii</Emphasis> and avermectins on the larvae of the colorado potato beetle <Emphasis Type="Italic">Leptinotarsa decemlineata</Emphasis> (Say) (Coleoptera,Chrysomelidae)

Synergy between the entomopathogenic fungus Metarhizium robertsii J.F. Bisch., S.A. Rehner et Humber and a complex of natural avermectins was observed after combined treatment of the Leptinotarsa decemlineata (Say) larvae. This effect was also recorded at the larval stage most resistant to fungi (5 days after molting to the IV instar). Intoxication with avermectins led to a 2.7-fold decrease in food consumption and arrest of larval development. Synergy between the fungus and avermectins was revealed in field experiments conducted in the steppe zone of Western Siberia under strong fluctuations of temperature and humidity. In particular, the median lethal time (LT₅₀) decreased 2.8-fold after combined treatment as compared to treatment with M. robertsii alone. The mechanisms of synergy and the prospects of using the combined treatment for Colorado potato beetle control are discussed.