The haploid males and diploid females of Hymenoptera have all chromosomes in the same proportions. This rules out most familiar sex-determining mechanisms, which rely on dosage differences at sex determination loci. Two types of model — genie balance and complementary sex determination (CSD) — have been invoked for Hymenoptera. Experimental studies provide no good evidence for genie balance models, which are contradicted by the detection of diploid males in 33 disparate species. Furthermore, recent advances have shown that sex determination in the best-studied diploid animals does not depend on genie balance, removing the original justification for hymenopteran genie balance models. Instead, several Hymenoptera have single-locus CSD. In this system, sex locus heterozyotes are female while homozygotes and hemizygotes are male. Single-locus CSD does not apply to several inbreeding species and this probably reflects selection against the regular production of diploid males, which are sterile. A multilocus CSD model, in which heterozygosity at any one of several sex loci leads to female development has also been proposed. To date, multilocus CSD has not been demonstrated but several biases against its detection must be considered. CSD can apply to thelytokous races as long as the cytogenetic mechanism permits retention of sex locus heterozygosity. However, some thelytokous races clearly do not have CSD. The distribution of species with and without CSD suggests that this form of sex determination may be ancestral in the Hymenoptera. However, phylogenetic analyses are hindered by the lack of data from several superfamilies and the fact that the internal phylogeny of the Hymenoptera remains controversial.

Single locus complementary sex determination (CSD) occurs in several species of Hymenoptera. Individuals that carry two different alleles (heterozygotes) are female while those with one and two copies of the same allele (hemizygotes and homozygotes) are haploid and diploid males, respectively. A multilocus model, in which diploids are only male if homozygous at all sex loci, has been proposed for species with regular but not exclusive inbreeding. To date, the only explicit test of the multilocus model is for Nasonia vitripennis. The latter is an inbreeding species in the Infra-order Parasitica and was shown not to conform to the multilocus model. In this study, inbreeding experiments are used to refute single and multilocus sex determination in a second inbreeding hymenopteran, Goniozus nephantidis (Infra-order Aculeata). Single locus CSD has been demonstrated in five other aculeates and G. nephantidis is the first aculeate species shown not to have CSD. The absence of CSD in G. nephantidis is probably a derived condition, favoured by the penalty of increased diploid male production under inbreeding.

In the HymenopteraDiadromus pulchellus diploid males have been observed in samples collected in the wild and bred in the laboratory. Using a yellow body color mutant strain, a protocol of crosses, involving inbred individuals, allows the routine production of such diploid males. These males result from the development of fertilized ova and emerge normally. Their preimaginal viability is similar to those of other individuals, and their imaginal viability does not differ from that of haploid males. Diploid males present normal external morphology and neither mosaicism nor intersexuality was observed. However, they are bigger than haploid males and have head size and wing length similar to those of females. The significance of diploid male viability in hymenopteran populations is discussed.

Summary

Inbreeding may have important consequences for the genetic structure of social insects and thus for sex ratios and the evolution of sociality and multiple queen (polygynous) colonies. The influence of kinship on mating preferences was investigated in a polygynous ant species, Iridomyrmex humilis, which has within-nest mating. When females were presented simultaneously with a brother that had been reared in the same colony until the pupal stage and an unrelated male produced in another colony, females mated preferentially with the unrelated male. The role of environmental colony-derived cues was tested in a second experiment where females were presented with two unrelated males, one of which had been reared in the same colony until the pupal stage (i.e., as in the previous experiment), while the other had been produced in another colony. In this experiment there was no preferential mating with familiar or unfamiliar males, suggesting that colony-derived cues might not be important in mating preferences. Inbreeding was shown to have no strong effect on the reproductive output of queens as measured by the number of worker and sexual pupae produced. The level of fluctuating asymmetry of workers produced by inbreeding queens was not significantly higher than that of non-inbreeding queens. Finally, colonies headed by inbreeding queens did not produce adult diploid males. Based on the current hypotheses of sex-determination the most plausible explanations for the absence of diploid-male-producing colonies are that (i) workers recognized and eliminated these males early in their development, and/or (ii) there are multiple sex-determining loci in this species. It is suggested that even if inbreeding effects on colony productivity are absent or low, incest avoidance mechanisms may have evolved and been maintained if inbreeding queens produce a higher proportion of unviable offspring.

Males of the hymenopteran Diadromus pulchellus are normally haploid, but diploid males can be obtained by inbreeding. Inbred crosses within strains that are polymorphic at the enzymatic loci Pgm-2 and Ao-4 or that differ by a body colour mutation produce heterozygous diploid males in offspring. The genotypic distributions observed in such progeny were compared with expected results under the one-locus sex determination model or the two independent loci model. The results show that only the one-locus multi-allele model fits the data and allow a provisional estimate of ∼ 15 sex alleles. These conclusions generalize the case of existence of a single locus to determine sex in Hymenoptera and are discussed at the evolutionary level.

DNA probes containing the repeated rDNA region ofDrosophila melanogaster (coding for e.g. 28S and 18S rRNA) hybridized in situ to distinct regions of two heterologous mitotic chromosomes of the honeybee, identifying the nucleolus organizing regions (NORs). The method allows a rapid establishment of a physical map ofApis mellifera using other DNA probes ofDrosophila. This is the first report on well-defined chromosomal markers in the honeybee.

Soilborne, fungal pathogens of cool season food legumes, including seed and seedling blights, rot rots, and wilts are described. Seed and seedling diseases are caused primarily by Pythium and Rhizoctonia spp. The most important fungi causing root rots include Aphanomyces euteiches, Fusarium solani, Pythium spp., Sclerotium rolfsii, and Macrophomina phaseolina. Wilt is caused primarily by various host-specific forms of Fusarium oxysporum. This paper discusses these diseases and screening procedures that emphasize standardization of inoculum levels, maintenance of virulent pathogen cultures, inoculum growth media, environmental conditions, and host plant age. Sources of resistance to these diseases are discussed.

The biology of the parasitic mite Tropilaelaps clareae Delfinado and Baker (Acarina: Laelapidae) was studied with a view to identify the time of invasion of the mite into the honey bee (Apis mellifera) brood and the threshold stage in the life cycle of the host. Honey bee brood was sequentially sampled on day 0, 4, 8, 12, 16 and 20 of development. Adult T. clareae infested the 8-day larva shortly before its cell was capped. The larvac, protonymphs, deutonymphs and adults of T. clareae were all found parasitising bright red eyed pupae during day 16 of brood development. This was identified as the most parasitised stage in the life cycle of the host. The mite developed from egg to adult in about 8 days.

We have developed a touch-fluorescence method using preparations from the outer surface of elevated and ulcerative malignant melanoma lesions. This method allows the demonstration of the melanogenic activity of melanoma cells within 30 min and has made it possible to definitively diagnose a lesion as malignant melanoma at the initial examination. In 21 cases clinically diagnosed as typical melanoma, 17 were definitively diagnosed as melanoma from the touch-fluorescence microscopic findings. Of the four cases in which no fluorescent tumor cells were found, two proved not to be melanoma. There was some correlation between the morbid types of primary melanoma and the configuration of fluorescent melanoma cells, the main cellular configuration of superficial spreading melanoma being round whereas that of nodular melanoma and acral lentigenous melanoma was pleomorphic. Based on the above results, this method was concluded to be extremely reliable for the preoperative diagnosis of elevated and ulcerative lesions of malignant melanomas, which are sometimes difficult to diagnose.