The microsporidium Nosema pyrausta as a potent microbial control agent of the beet webworm Loxostege sticticalis.

The microsporidium Nosema pyrausta is an important mortality factor of the European corn borer, Ostrinia nubilalis. The present study was aimed at N. pyrausta virulence testing to the beet webworm (BW), Loxostege sticticalis. This agricultural pest, L. sticticalis, was highly vulnerable to N. pyrausta. The parasite's spores were located in salivary glands, adipose tissue, and Malpighian tubules of the infected specimens. Infection was transmitted transovarially through at least 3 laboratory generations, in which BW fitness indices were lower than in the control, and moth emergence and fertility decreased prominently. Transovarial infection was most detrimental to female egg-laying ability, resulting in zero fertility in F3. When propagated in BW, the microsporidium tended to increase its virulence to L. sticticalis, as compared to the Ostrinia isolates. The parasite's ability to infect this host at low dosages and transmit vertically should guarantee its effective establishment and spread within BW populations. In conclusion, N. pyrausta is a promising agent against BW, which is a notorious polyphagous pest in Eurasia.

Combined effect of the entomopathogenic fungus Metarhizium robertsii and avermectins on the survival and immune response of Aedes aegypti larvae.

Combination of insect pathogenic fungi and microbial metabolites is a prospective method for mosquito control. The effect of the entomopathogenic fungus Metarhizium robertsii J.F. Bischoff, S.A. Rehner & Humber and avermectins on the survival and physiological parameters of Aedes aegypti (Linnaeus, 1762) larvae (dopamine concentration, glutathione S-transferase (GST), nonspecific esterases (EST), acid proteases, lysozyme-like, phenoloxidase (PO) activities) was studied. It is shown that the combination of these agents leads to a synergistic effect on mosquito mortality. Colonization of Ae. aegypti larvae by hyphal bodies following water inoculation with conidia is shown for the first time. The larvae affected by fungi are characterized by a decrease in PO and dopamine levels. In the initial stages of toxicosis and/or fungal infection (12 h posttreatment), increases in the activity of insect detoxifying enzymes (GST and EST) and acid proteases are observed after monotreatments, and these increases are suppressed after combined treatment with the fungus and avermectins. Lysozyme-like activity is also most strongly suppressed under combined treatment with the fungus and avermectins in the early stages posttreatment (12 h). Forty-eight hours posttreatment, we observe increases in GST, EST, acid proteases, and lysozyme-like activities under the influence of the fungus and/or avermectins. The larvae affected by avermectins accumulate lower levels of conidia than avermectin-free larvae. On the other hand, a burst of bacterial CFUs is observed under treatment with both the fungus and avermectins. We suggest that disturbance of the responses of the immune and detoxifying systems under the combined treatment and the development of opportunistic bacteria may be among the causes of the synergistic effect.

Bacterial and fungal infections induce bursts of dopamine in the haemolymph of the Colorado potato beetle Leptinotarsa decemlineata and greater wax moth Galleria mellonella.

Dopamine (DA) is known as a hormone neurotrasnmitter molecule involved in several stress reactions in both vertebrates and invertebrates. Following infections with the fungi Metarhizium robertsii or Beauveria bassiana and the bacterium Bacillus thuringiensis, dopamine the concentration was measured at different time points in the haemolymph of the Colorado potato beetle, Leptinotarsa decemlineata and the larvae of the greater wax moth Galleria mellonella. The infection with M. robertsii increased (4 to 12-fold) DA concentrations in the haemolymph of the potato beetle larvae and the oral infection by B. thuringiensis also lead to a 30 and 45-fold increase. During infection of the greater wax moth larvae with Beauveria bassiana and B. thuringiensis DA increased 4 to 20-fold and about 2 to 2,5-fold respectively, compared to non-infected insects. The relative DA concentrations varied between the two insects and depended on the pathogens and post infection time.

Maintenance of redox balance by antioxidants in hemolymph of the greater wax moth Galleria mellonella larvae during encapsulation response.

The lipid peroxidation process in hemocytes, activities of phenoloxidase and key enzymatic antioxidants (superoxide dismutase, glutathione-S-transferase, catalase) and nonenzymatic antioxidants (thiols, ascorbate) in hemolymph of the greater wax moth Galleria mellonella L. (Lepidoptera: Pyralidae) were studied during the encapsulation process of nylon implants. It has been established that as soon as 15 min after piercing a cuticle with the implant, a capsule is formed on its surface. Active melanization of the capsule has been shown to last for 4 h. During the first hours after incorporating the implant, an increase in phenoloxidase activity and lipid peroxidation in the insect hemocytes has been revealed. Adhesion and degranulation on the surface of foreign object lead to the depletion of total hemocytes count (THC). Our results indicated that thiols and ascorbate molecules take part in the immediate antioxidant response, during later stages of encapsulation process hemolymph glutathione-S-transferase detoxifies and protects insect organism thereby restoring the internal redox balance. We suggest that nonenzymatic and enzymatic antioxidants of hemolymph plasma play a key role in the maintenance of redox balance during encapsulation of foreign targets.

VENOM FROM THE ECTOPARASITIC WASP Habrobracon hebetor ACTIVATES CALCIUM-DEPENDENT DEGRADATION OF Galleria mellonella LARVAL HEMOCYTES.

Ectoparasitoids inject venom into hemolymph during oviposition. We determined the influence of envenomation by the parasitoid, Habrobracon hebetor, on the hemocytes of its larval host, Galleria mellonella. An increase in both intracellular Са(2+) content and phospholipase C activity of the host hemocytes was recorded during 2 days following envenomation by the parasitoid. The decreased hemocyte viability was detected 1, 2, and 24 h after the envenomation. Injecting of the crude venom (final protein concentration 3 µg/ml) into the G. mellonella larvae led to the reduced hemocyte adhesion. The larval envenomation caused a decrease in transmembrane potential of the hemocytes. These findings document the suppression of hemocytic immune effectors in the parasitized host larvae.