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Two forest pests appear to become partially resistant to the insect toxins produced by Bacillus thuringiensis. Both Thaumetopoea pityocampa and Lymantria monacha lose binding sites for the Cry1Ab toxin during larval development.

Bacillus thuringiensis produces crystalline inclusions comprised of a mixture of delta-endotoxins during sporulation. Following ingestion by insect larvae, these inclusion proteins are solubilized, and the protoxins are converted to toxins. Research findings showed a greater extent of oligomerization of the Cry1Ac toxin with vesicles from the Heliothis virescens midgut than with those from the Manduca sexta midgut, which correlated with observed differences in toxicity. Tight binding of virtually the entire toxin molecule to the membrane is an important step in toxicity.

A susceptible strain of diamondback moth and resistant strains of diamondback moth from the Philippines, Hawaii and Pennsylvania were subjected to competitive binding tests. A model which includes at least four binding sites involved in binding of Cry1Aa, Cry1Ab, Cry1Ac, Cry1B, Cry1C and Cry1F was proposed. Results showed that in each of the three resistant strains, the common binding site is altered. In the strain from the Philippines, the alteration reduced binding of Cry1Ab but not of the other crystal proteins, while in the resistant strains from Hawaii and Pennsylvania, the alteration affected binding of Cry1Aa, Cry1Ab, Cry1Ac, Cry1B and Cry1F.

An examination of larvae of the oil fly, Helaeomyia petrolei, from the asphalt seeps of Rancho La Brea in Los Angeles, CA, for microbial gut contents revealed that these contain ca 2 x 10(super 5) heterotrophic bacteria. The bacteria found in oil fly larvae are neutrophiles, facultative or obligate aerobes and nonsporeformers, almost all of which are gram negative. Acridine orange staining showed that the culturable bacteria represented 15% to 20% of the total population. There was no evidence found that the 14 isolates chosen grew on derived nutrients from the asphalt or that they had a major role in insect development.

The Bacillus thuringiensis-produced Cry1Ab and the Cry1Ac toxins fail to show any differences in their binding to the protein of ca.80-kDa in Plodia interpunctella strains resistant to the toxins. The binding protein is necessary for toxicity and differs in size from the aminopeptidase N antigens responsible for binding in other insects. The toxins bind to the membranes of susceptible larvae but not to those of resistant larvae. This indicates that the resistant P. interpunctella strains have altered accessibility of Cry1A-binding protein rather than altered binding properties.

Preoccluded virus forms (POV) of baculoviruses are more potent in infecting host larvae than wild-type viruses and are easily stabilized and produced in larval tissue. Almost 50% of the potency of the wild-type-virus is due to the occluded polyhedra and the rest is due to the POV in the tissue. The polyhedrin-negative viruses are more infectious than the wild-type and their potency is unaffected by lyophilization. The POVs are unstable in dead larval tissues. The ability of POV to infect larvae opens up possibilities for their use as biopesticides.

European foulbrood is a disease that attacks four- to five-day-old honeybee larvae. The Melissococcus pluton bacterium has been recognized as the cause of this disease. A fast and accurate method for the identification of the bacterium directly from diseased honeybee larvae is described. It uses polymerase chain reaction primers developed from the 16S rRNA gene of the bacterium. The technique takes six hours to complete following overnight incubation of the bee larvae and is particularly valuable given the difficulty in isolating and identifying the bacterium.

The digestive tract of humus-feeding scarab beetle larvae shows considerable parallels to the situation in soil-feeding termites, particularly with respect to the alkaline gut regions. The gut pf Pachnoda ephippiata larvae harbors a dense and diverse microbiota, which differs considerably among the major gut regions and from that in the soil, fed to the larvae.

A report on the community structure of bacteria and archaea in the midgut, hindgut, and food soil of Pachnoda ephippiata larvae, determined with cultivation-independent techniques is presented. Analysis revealed that the intestines of Pachnoda ephippiata larvae contain a complex gut microbiota that differs markedly between midgut and hindgut and that is clearly distinct from the microbia in the food soil.