Factors other than Light Affecting the Pineal Gland: Hypophysectomy, Testosterone, Dihydrotestosterone, Estradiol, Cryptorchidism, and Stress

This article reviews those factors other than light that affectthe activity of the pineal gland. Both testosterone and dihydrotestosteronewere shown to have tissue specific inhibitory effects on pinealMAO activity concomitant with an increased activity of the gland.Estradiol stimulated pineal MAO activity and decreased the activityof this gland. This effect also was tissue-specific. Bilateraland unilateral experimental cryptorchidism also decreased pinealMAO activity 3 to 4 weeks after surgery. Acute stresses appearto increase adrenal catecholamine output (epinephrine and norepinephrine)as well as to stimulate local adrenergic pathways, while chronicstress, such as starvation, appears to act through the adrenalcorticosteroids by decreasing pineal MAO activity thereby indirectlyincreasing melatonin synthesis. Thusly, both components of theadrenal gland appear to act in concert to increase effectivelymelatonin synthesis by the pineal gland. Irradiation and histaminehave also been reported to affect pineal function—thelatter specifically inhibits HIOMT activity. These observationsindicate that many factors other than light affect pineal morphologyand melatonin synthesis. The pineal appears to be a true neuroendocrineorgan that is affected by hypophysectomy and is responsive tofeedback and control from other organs within the mammalianorganism.     

Host-plant susceptibility to the carrot fly, Psila rosae. 2. Suitability of various host species for larval development

Several apiaceous and two asteraceous species were tested for their suitability to support larval development of the carrot fly. Plants grown in pots or transplanted from seed beds into pots, were inoculated with a specific number of eggs. Pupae and non-pupated larvae were collected 6–7 wk after inoculation. Both the number and weights of pupae produced varied widely among the species. Cultivated carrots Daucus carota sativus often gave rise to only moderate numbers of pupae, but these invariably attained the highest weights. Pimpinella major was the only apiaceous plant tested that did not yield any carrot flies. The two asteraceous plants Cichorium intybus and Tanacetum vulgare failed to support larval development. Total carrot fly biomass produced per plant was influenced by both the host species and the root weight. Emergence rates of adult flies were positively correlated with pupal weights. Small individuals tended to have a longer total developmental time from egg to adult fly.     

The influence of genetic background on resistance to the cabbage aphid (Brevicoryne brassicae) in Kale (Brassica oleracea var. acephala)

Resistance to Brevicoryne brassicae has been identified in the progeny of two selected kale (B. oleracea var. acephala) plants, one from the F1 hybrid cultivar ‘Arsis RS’ and one from the landrace ‘Butzo’. These plants were crossed with susceptible B. oleracea morphotypes that have different periods to flowering. The type of susceptible plant line used had an effect on the resistance phenotypc of the progeny. Tested F2 populations derived from these crosses show that resistance is not under simple genetic control. This, in addition to variation in aphid numbers within accessions, suggests that separation of genetic components of control from environmental ‘noise’ for any accession may only be possible by the production of double haploid plant lines.     

Drosophila melanogaster males respond differently at the behavioural and genome‐wide levels to Drosophila melanogaster and Drosophila simulans females

Drosophila melanogaster are found in sympatry with Drosophila simulans, and matings between the species produce nonfertile hybrid offspring at low frequency. Evolutionary theory predicts that females choose mates, so males should alter their behaviour in response to female cues. We show that D. melanogaster males quickly decrease courtship towards D. simulans females. Courtship levels are reduced within 5 min of exposure to a heterospecific female, and overall courtship is significantly lower than courtship towards conspecific females. To understand changes at the molecular level during mate choice, we performed microarray analysis on D. melanogaster males that courted heterospecific D. simulans females and found nine genes have altered expression compared with controls. In contrast, males that court conspecific females alter expression of at least 35 loci. The changes elicited by conspecific courtship likely modulate nervous system function to reinforce positive conspecific signals and dampen the response to heterospecific signals.     

The influence of plant age on resistance of radish to cabbage root fly egg-laying

Cabbage root fly ( Delia brassicae ) egg-laying around radish plants ranging in age from newly emerged seedlings to plants with flowering shoots was studied in the field and laboratory. The attractiveness of radish changed with age, one peak in egg-laying occurring just before plants were of marketable size and further peaks as they produced flowering shoots. The pattern of egg-laying was similar for the six radish cultivars tested, both in the field and laboratory, irrespective of whether flies did or did not have a choice of plants of different ages. At any one age, there was no correlation between egg-laying and plant size. Selection within radish cultivars for the extremes of the range of egg-laying preference appeared to alter the cycle of attractiveness of different radish stocks to cabbage root fly, the response being influenced by environmental conditions.