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The insecticidal potential of various entomopathogenic bacteria was evaluated by ingestion and/or injection bioassays against noxious insects including Musca domestica, Ceratitis capitata, Lymantria dispar, and Malacosoma neustria. Bacteria involved in the study included newly isolated soil occurring strains, reference strains (i.e. Bacillus thuringiensis, Brevibacillus laterosporus, Photorhabdus luminescens and Xenorhabdus nematophila), and others isolated form Galleria mellonella larvae infected with an original collection of entomopathogenic nematods. The new bacterial isolates were identified by phylogenetic analysis involving 16S rRNA gene sequencing. As a result of bioassays, significant differences in the insecticidal potential emerged for diverse bacterial strains and different insect targets. B. thuringiensis, P. luminescines and X. nematophila were generally highly toxic against lepidopteran larvae, while different B. laterosporus strains showed variable degrees of toxicity against the house fly. Among the others, significant was the pathogenic potential of Bacillus firmus, Paenibacillus tundrae and Bacillus psychrodurans, and of new species belonging to the genera Serratia, Pseudomonas, Stenotrophomonas and Alcaligenes. These results are discussed in comparison with previous knowledge in the field, highlighting the prospect of a possible use of new bacterial strains for further studies focusing on the development of new actives for the microbial pest management.

Si riporta una sintesi delle indagini condotte in sugherete della Sardegna sui principali lepidotteri defogliatori. Le specie che causano danni di un certo rilievo sono Lymantria dispar L. e Malacosoma neustria (L.), con infestazioni di tipo periodico, e Tortrix viridana L., con fluttuazioni di tipo temporaneo. La periodicità delle gradazioni di L. dispar, studiata con il conteggio delle ovature, ha avuto un’ampiezza variabile fra 11 e 5-6 anni nei diversi comprensori subericoli dell’Isola, probabilmente per le differenti condizione di conservazione degli equilibri naturali nei singoli ambienti indagati. Sono inoltre illustrati i risultati di prove di lotta microbiologica condotte contro questo defogliatore con preparati a base di Bacillus thuringiensis kurstaki. Dosi superiori a 30 miliardi di U.I. per ettaro hanno determinato elevate mortalità larvali (anche superiori all’80%) mentre la distribuzione di soli 16 miliardi di U.I./ha non ha garantito un’efficace protezione della vegetazione. I preparati microbiologici saggiati nel corso di 5 anni di sperimentazione non hanno avuto nessun effetto negativo diretto sull’entomofauna utile.

Data are given on the biology, mortality factors and population dynamics of Lymantria dispar L., Malacosoma neustria L., Tortrix viridana L. and Euproctis chrysorrhoea L. the most harmful lepidopters to Quercus suber L. A revision of chemical, microbiological, biological, biotechnical and genetic control methods applied in the relevant diffusion areas is also reported.

Lepidopter infestation of Northern Sardinian cork-oaks was studied from 1964 to 1975. Data were obtained on population composition, factors influencing natural mortality, fluctuation rythms of the more important species, and on plant reaction to defoliation. 67 species were observed, of which the most frequently noted phytophagous lepidopters were: (1) Dryobotodes eremita Fabr. and D. Monochroma Esp., - with latent fluctuation; (2) Tortrix viridana L., Ortollosia cruda Schiff. and Spudaea ruticilla Esp., - with temporary fluctuation; and (3) Phalera bucephala L., Malacosola neustria L. and Porthetria dispar (L.), - with periodic fluctuation. P. dispar (L.) and M. Neustria L. fluctuations occurred in cycles of approximately 9 years. Severe defoliation was observed in 1973 and 1974, Malacosoma reaching maximum population density a year earlier than Porthetria. Numerous natural mortality factors affected the population fluctuation of Porthetria. Particularly significant was the impact of predators and parasites on the pre-imaginal stages as well as that of pathogenetic agents (e.g. viruses, protozoa), although the effect of the latter varied from year to year and was not entirely related to larval population density. Apart from a 7- 10% sterility, eggs showed a mortality rate varying from 2.7% to 17.7% due to the parasites Ooencyrtus kuwanai (How.) (Hym., Encyrtidae) and Anastatus disparis Ruschka (Hym. Eupelmidae) and the predators Dermestes lardarius L. (Col. Dermestidae) and Haplocnemus jejunus Kiensenw. (Col. Melyridae). The numbers of parasites on the larvae were in direct proportion to the larval population density and varied from 4.8% to 80.5 %; the most frequently encountered were Sturmia scutellata R.D., Exorista segregata Rond., Exorista larvarum L. (Dipt. Tachinidae) and Sarcophagidae of Agria and Sarcophaga genera. The predator Calasoma sychophanta L. (Col. Carabidae) appeared in large numbers the year following a maximum population density of the host larva. In addition to the forementioned dipters, the following were also observed to emerge from the Porthetria chrysalides: Pales pavida Meig. (Dipt. Tachinidae), Muscina stabulans Fall. (Dipt. Muscidae), Pimpla instigator F., Theronia atalantae Poda (Hym., Ichneumonidae) and Brachymeria intermedia (Nees) (Hym., Chalcididae). Porthetria population fluctuations were also affected by ambiental factors and by a reduction in fecundity when population densities were at their highest. Malacosoma neustria L., apart from being subject to the same parasites and pathogenetic agents as Porthetria, was particularly influenced by Pales pavida Meig. and Scambus malacosomae Seyrig (a hymenopter parasite specific to Malacosoma larvae in cocoon). Gradations in the two defoliator populations are, therefore, regulated by a whole number of contemporary factors in which tachinids, ichneumonids and disease play the predominant role. Provided that spring rainfall exceeds 180 mm, completely defoliated cork-oaks recover their foliage within 15 to 20 days. The damage caused by parasitic attack is, thus, limited to a certain extent. As a result of the observations made on the dynamics and regulating factors of the main forest defoliator populations, it is proposed that specific chemical control be confined (1) to the years of progradation, (2) to the period when the young larvae are present and (3) only to certain limited surfaces considered strictly necessary.