Suppression of pederin biosynthesis through antibiotic elimination of endosymbionts in Paederus sabaeus.

Biosynthesis of the unique defensive compound pederin is confined to female rove beetles of the genus Paederus (Coleoptera: Staphylinidae). These (+)-females endow their eggs with toxin whereas (-)-females, which occur both naturally and in laboratory reared specimens, do not. The latter are aposymbionts lacking biosynthetic capabilities because of endosymbiotic deficiency. They can, however, be induced to accumulate pederin if fed with (+)-eggs during larval development. The endosymbionts can thus be transmitted by ingestion of (+)-Eggs. (+)-eggs treated with benzylpenicillin, erythromycin, oxytetracycline or streptomycin show that the induction of pederin accumulation depends on the antibiotic's spectrum of efficaciousness, its dosage and duration of the treatment. Certain bacteria, probably belonging to the gram-negative type, must be transmitted to produce (+)-females.

Possible genetic basis of pederin polymorphism in rove beetles (Paederus riparius).

In Paederus riparius, (+) females able to biosynthesize the unique hemolymph toxin pederin and (-) females lacking this ability co-occur in natural populations. Larvae descended from both types of females were reared in the laboratory and the imagoes were crossed in order to get information about a possible genetic basis of this polymorphism. The daughters of (+) mothers become (+) females or (-) females, while the progeny of (-) mothers comprises only (-) females. This suggests a matrilineal trait because pederin biosynthesis cannot be inherited from the father. The rather stable proportion of nearly 90% (+) females in collected females is not maintained, however, when the beetles are reared in the laboratory. This observation is discussed with regard to artificial rearing conditions, where individuals are kept separate and cannot prey on conspecifics.

Allocation of pederin during lifetime ofPaederus rove beetles (Coleoptera: Staphylinidae): Evidence for polymorphism of hemolymph toxin.

Pederin, a hemolymph toxin found in the rove beetle genusPaederus, is quantified in individual specimens ofP. fuscipes andP. riparius. Whereas males always contain only small quantities of the toxin (0.1-1.5 µg), females are not so restricted (0.2-20.5 µg) and in most cases possess roughly 10-fold that in males. There are, however, females containing as little pederin as the males, and so two clearly separate groups of females can be discerned. These two groups hint at two types of females defined by the eggs they lay. About 85% of the females, i.e., those containing much of the substance, transfer pederin into every egg and thus are denoted (+)-females. The remaining 15%, the (-)-females, contain at best small amounts of the toxin, which is transferred in minute quantities into the first eggs while the subsequent ones lack pederin. With respect to the pederin content of their eggs, there is no overlap between these two types of females. If fed with pederin, (-)-females can transfer it into the eggs like (+)-females. After hatching the larvae store pederin when present. Larvae are not able to biosynthesize the toxin on their own, but storage of that received in the egg is very efficient, and the difference between larvae with and without pederin is preserved until imaginal eclosion. In (+)-females, pederin increases, probably reflecting a biosynthetic capacity, but in males and presumptive (-)-females the amount of pederin never exceeds the quantity transferred by parental (+)-females. Consequently, males and (-)-females probably are unable to biosynthesize pederin. This polymorphism of females may have a genetic basis. Individuals of all stages nevertheless sequester pederin if it is supplied with the diet.