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The activity of four mycotoxins extracted from Beauveria bassiana, Paecilomyces fumosoroseus and Nomuraea rileyi and a bacterial exotoxin of Bacillus thuringiensis var. thuringiensis were assayed for activity on larvae of the greater wax moth and the gypsy moth. The procedure for toxin extraction was described and toxins were administered via. topical application and intrahemocoelic injection. Larvae of the wax moth showed higher mortality rates, and in general, high levels of toxicity were recorded in both species. Zusammenfassung Wirkungen von Mikroben-Toxinen auf die Larven des Schwammspinners und der grosen Wachsmotte Es wurde die Aktivitat der toxischen Extrakte von 4 Mikroorganismen: Beauveria bassiana, Paecilomyces fumoso-roseus, Nomuraea rileyi und Bacillus thuringiensis var. thuringiensis auf die Larven des Schwammspinners und der grosen Wachsmotte untersucht. Die Methodik der Toxin-Extraktion und der topikalen sowie intrahaemocoenalen Injektion der Toxine werden beschrieben. Die Larven der grosen Wachsmotte zeigten hohere Sterblichkeitsraten als jene des Schwammspinners. Allgemein wurde eine hohe Wirksamkeit der Toxine aller 4 Mikroorganismen gegenuber den Larven beider Schmetterlingsarten festgestellt.

Second-instar larvae of the gypsy moth, Porthetria dispar (L.) were infected with Beauveria bassiana (Balsamo) Vuill. by allowing larvae to crawl over sporulating cultures of the fungus. Virulence of the pathogen was increased by inoculating larvae of the wax moth, Galleria melonella (L.), twice in serial succession. Observations were made on the infectivity and histopathology of the parasite in the host. Penetration of the cuticle occurred 24 h after inoculation and at 64 h post-inoculation the interior was completely filled with hyphae. Penetration of the gut wall was also observed.

Fourth instar larvae of the gypsy moth,Porthetria dispar (L.) were infected with the fungusConidiobolus coronatus(Cost.) Batko using the spore shower technique for varying periods of time. Larvae treated for more than 20 minutes showed 100% mortality. Virulence of the pathogen was increased by inoculating larvae of the wax moth,Galleria mellonella (L.) three times in serial succession. Typical symptoms of the infection were lightening of color, flaccidity, shrinking and finally desiccation of the larvae. Observations on the histopathology of infected larvae showed penetration of the integument by hyphae within 22 hours after inoculation and at 34 hours post inoculation, the hemocoel, head, nervous system and muscles were completely infected. A localized mycelial growth in the digestive system resulted probably due to the ingestion of spores, but penetration of the gut wall was not recorded.

Larvae of the gypsy mothPorthetria dispar (L.) were infected with sporulating cultures of the fungus,Entomophthora virulentaHall & Dunn using the spore shower technique. The infectivity of the parasite in the host and its histopathology was observed. Penetration of the integument was recorded at 24 hours post-inoculation and conidiophore production occurred at 72 hours after infection. Experiments on mammalian toxicity against laboratory mice showed no significant differences between control and treated mice in body weight, blood cell counts, food and liquid consumption and in the post-mortem examination.

Inhibition by 14 isolates of nine species of entomogenous fungi against two strains of the Dutch elm fungus, Ceratocystis ulmi (aggressive and non-aggressive), was evaluated under laboratory conditions. Eleven of the 14 inhibited one or both strains of C. ulmi. Different levels of antagonism were observed at different light levels and temperatures. Beauveria bassiana, Metarhizium anisopliae, and Nomuraea rileyi were antagonistic to both strains of C. ulmi under the four tested combinations of light and temperature. Metarhizium anisopliae produced the highest qualitative level of inhibition. The growth rate of the cultures differed Conventional control measures for the Dutch elm disease (DED) have em- phasized control of the insect vectors, Scolytus scolytus Fabr. and Scolytus mul- tistriatus Marsham, mainly due to the inaccessibility of the pathogen, Ceratocystis ulmi (Buis.) Moreau in the xylem vessels of the elm (Holmes, 1980). Several workers (Doane, 1959; Barson, 1976,1977; Doberski, 1981) have reported patho- genicity in tests for control of the DED insect vectors by the entomogenous fungi, Beauveria bassiana (Bals.) Vuill., Metarhizium anisopliae (Metsch.) Sorokin, Pae- cilomyces farinosus (Dicks ex Fr.) Vuill., and Verticillium lecanii (Zimm.) Viegas. The possible use of these entomogenous fungi in biological control of DED requires investigation of antagonistic interactions between vector and control agent, and also between C. ulmi and each entomogenous fungus. Gibbs and Smith (1978) and Webber (1981) identified several fungal antagonists of C. ulmi. The bacterium, Pseudomonas syringae van Hall, has also demonstrated in vivo an? tagonism in studies by Myers and Strobel (1983), and earlier Holmes (1954) showed Bacillus polymyxa to be an effective inhibitor. The objectives of the present study were to assess the interactions between potential vector control agents (such as entomogenous fungi), and two strains of C. ulmi. Fungal antag? onists of C. ulmi would be efficiently brought into action if they were transported