Many species of tenebrionid beetles produce and secrete benzoquinones from specialized prothoracic and postabdominal glands. Tribolium confusum produces two compounds methyl-1,4-benzoquinone (MBQ) and ethyl-1,4-benzoquinone (EBQ). These compounds are hypothesized to function as external defense compounds, killing microbes and deterring predators, and their ability to evolve by natural selection depends on both selection and the genetic vs. environmental contribution to phenotypic variation. We crossed a strain of T. confusum that produces high quantities of benzoquinones, b-Pakistan, with a low-producing strain, b-+, and measured both the internal and external quantities of MBQ and EBQ for the two extreme strains and their F1 progeny. Internal amounts show a clear pattern of inheritance, with at least 50% of the phenotypic variation attributed to genotype. Additive and dominance coefficients for internal amounts indicate that the trait is additive with no significant dominance. In contrast, external quantities show little pattern of inheritance. The role of genetics and environment in determining quantities of secretory defensive compounds is important to elucidating the ecology and evolutionary potential of chemical defenses.

Insects often produce chemicals, such as defensive compounds, whose quantity and distribution can affect their fitness. For evolution to produce adaptations, chemical production must be genetically variable. Here we report the results of a study using high-performance liquid chromatography to quantify two important chemical secretions of the flour beetle Tribolium confusum, methyl-1, 4-benzoquinone (MBQ) and ethyl-1,4-benzoquinone (EBQ). Our results show a distinct difference in the production of the compounds among four genetically distinct strains of T. confusum (b-+, b-I, b-IV, b-Pakistan) with an unusually high amount measured for the b-Pakistan strain. By measuring internal and external benzoquinone levels separately, we were also able to detect differences in production and distribution of the compounds between the strains. Some strains secrete more of the chemicals, whereas other strains appear to sequester the compounds within their bodies. The sexes also differ in total quinone production as well as in their internal to external benzoquinone ratios, suggesting the trait is sex influenced. Finally, a consistent correlation in the amounts of MBQ to EBQ in individual beetles suggests that the substituted benzoquinones share a common precursor or pathway.

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Benzylic zinc reagents add with high regioselectivity to 1‐(phenoxycarbonyl) salts derived from pyridine‐3‐carboxaldehyde (1a) or 3‐acetylpyridine (1b) to yield 1‐(phenoxylcarbonyl)‐4‐benzyl‐1,4‐dihydropyridine‐3‐carboxaldehydes 5a, 5c or ketones 5b, 5d. Aromatizations of these dihydro analogues with sulfur led to the corresponding aldehydes 6a, 6c or ketones 6b, 6d. An alternate synthesis to the aldehydic precursors involved additions of benzylic zinc reagents to 1‐(phenoxycarbonyl) salts formed from methyl nicotinates which led to the corresponding methyl 1‐(phenoxycarbonyl)‐4‐benzyl‐1,4‐dihydronicotinates 7a, 7b. Aromatizations of 7a, 7b led to the corresponding pyridine esters 8a, 8b which on reduction with lithium aluminum hydride yielded the corresponding carbinols 9a, 9b. Oxidation of 9a, 9b by manganese dioxide afforded aldehydes 6e, 6f. Aldehydes 6a‐f were readily converted into the benz[g]isoquinolines 10a‐f on heating in polyphosphoric acid.

A convenient synthetic pathway to benzo[g]quinolines (1‐azaanthracenes) has been developed. The nickel catalyzed coupling of methyl 2‐chloronicotinate (3a) with benzylic organo zinc reagents 2a‐e led to the methyl 2‐benzylic substituted nicotinates 4a‐e. Treatment of methyl 2‐chloro‐6‐methylnicotinate (3b)with 2a in a similar manner led to methyl 2‐benzyl‐6‐methyInicotinate (4f). The coupling of 2‐chloro‐3‐acetylpyridine (5) with benzyl zinc bromide (2a) led to 2‐benzyl‐3‐acetylpyridine (4g). The coupling of the 2,5‐dichlorobenzylic organic zinc reagent (2f) with methyl 2‐choronicotinate (3a) was unselective but readily coupled with methyl 2‐bromonicotinate (6) to yield methyl 2‐(2,5‐dichlorobenzyl)nicotinate (4h). The esters 4a‐f,h on reduction with lithium aluminum hydride led to the corresponding alcohols 7a‐f,h which were subsequently oxidized with manganese dioxide to the respective 2‐benzylic substituted pyridine‐3‐carboxaldehydes 8a‐f,h. In one case the coupling of benzy] zinc bromide (2a) with 2‐chloropyridine‐3‐carboxaldehyde (9) led directly to 2‐benzylpyridine‐3‐carboxaldehyde (8a), but in poor yield. Cyclizations of the aldehydes 8a‐d,f,h or the ketone 4g with polyphosphoric acid afforded the benzo[g]quinolines 10a‐d,f‐h in high yields. Aldehyde 8e was cyclized to 10e using a solution of sulfuric acid in methanol. Several of the benzo[g]quinolines 10c,d could be readly converted into the benzo[q]quinoline‐5,10‐diones 11c,d on treatment with ammonium ceric nitrate.