Edwin P. Marks

Pesticides: Insecticides and Fungicides Are Chitin Synthesis Inhibitors

Several important groups of fungicides and insecticides are specific inhibitors of chitin synthesis in a Phycomyces enzyme system and in insect organ cultures. The recently discovered benzoylphenylurea insecticides, which prevent chitin synthesis in insect tissues, are apparently not direct-acting chitin synthetase inhibitors. These insecticides may prevent insect chitin synthesis by interfering with the proteolytic activation of the chitin synthetase zymogen.

An in vitro system for the quantitative measurement of chitin synthesis in the cockroach: Inhibition by TH 6040 and polyoxin D

Abstract The β-ecdysone-dependent in vitro synthesis of chitin by cockroach leg regenerates was confirmed by chemical analysis and provides a sensitive, quantitative bioassay for inhibitors of chitin synthesis or materials with molting hormone activity via 14 C-N-acetylglucosamine incorporation. Chitin synthesis in insect tissue was inhibited (I 50 ) by TH 6040 at 6·11 × 10 −10 M and by polyoxin D at 7·53 × 10 −7 M. An investigation of the low I 50 of TH 6040 showed that it partitions out of culture medium into tissue. This suggests that this compound may be magnified in food chains.

The effect of β-ecdysone on insect neurosecretion in vitro

Abstract Cultured brains of late instar larvae of Madeira cockroaches, Leucophaea maderae , rapidly accumulated neurosecretory material in the perikarya and axons of the median neurosecretory cells. Treatment with the hormone β -ecdysone prevented this accumulation by causing the cells to release their products as rapidly as they were formed.

The action of hormones in insect cell and organ cultures.

Abstract A review of the literature of the action of hormones on insect tissues in vitro published between 1915 and 1970 indicates that research has been concerned with four main areas: studies of the development of imaginal discs, studies of morphogenesis and cuticle secretion in epidermal tissues, studies of the development of gonads, and studies of secretory activity in endocrine glands. The progress made in each field and the possibilities of further investigations are discussed.

ESTABLISHMENT OF TWO CELL LINES FROM EMBRYONIC TISSUE OF THE TOBACCO HORNWORM, MANDUCA SEXTA (L.)

SummaryTwo cell lines were derived from primary cultures of embryonic tissue of the tobacco hornworm,Manduca sexta (L.). The cell lines were maintained on hemolymph-free synthetic insect medium. Cytogenetic and immunological identification of the lines were carried out. Techniques for obtaining the line and medium, subculturing and freezing procedures for long-term storage, and the morphological and growth characteristics are described.

Effects of ecdysterone in vitro on hindgut and hemocytes of Manduca sexta (Lepidoptera)

Tissues from the tobacco hornworm, Manduca sexla (Johannson), were maintained in vitro for up to 10 months. When treated with the molt-stimulating hormone ecdysterone (β-ecdysone), these tissues underwent morphogenetic changes that closely resembled those normally occurring in vivo. However, when treated with the inactive isomer 22-isoecdysone, no such changes occurred. When tissues from lastinstar larvae were treated, the changes were characteristic of those occurring during the larval-pupal transformation; and when tissues from diapausing pupae were treated, the changes were characteristic of those that occur during the pupal-adult transformation. Hemocytes also responded to treatment with an increase in migratory activity.

Ecdysone action on insect cell lines

SummaryCell lines derived from embryos of the tobacco hornworm,Manduca sexta (L.), showed a marked morphological response to treatment with physiological doses of β-ecdysone. The response of these cell lines with α-ecdysone indicated that the penta-ol (α-ecdysone) must be converted to the hexa-ol (β-ecdysone) form before the morphological response can appear. Liquid chromatographic analysis of the spent medium confirmed that the cells converted the α-ecdysone to β-ecdysone in amounts that exceeded the threshold level for a biological response. Constant exposure to β-ecdysone produced a cell line that was resistant to the killing effect of β-ecdysone and failed entirely to respond to the presence of α-ecdysone.

Synthesis and storage of a neurohormone in insect brains in vitro

Abstract The build-up of neurosecretory material in the median neurosecretory cells and fibre tracts of cultured cockroach brains was demonstrated by staining and bioassay. Examination of the cultured brains by electron microscopy showed active production of neurosecretory granules after 3 days in vitro. The close correlation of the results obtained by these different methods of assay leaves little doubt that a neurohormone is being synthesized and stored.

Regenerating tissues of the cockroach Leucophaea maderae: effects of humoral stimulation in vitro.

A series of experiments was devised to test the effects in vitro of endocrine gland incubates on leg regenerate tissues from the cockroach Leucophaea maderae F. Incubates of increasing numbers of prothoracic glands produced increasing effects on the test tissues. Stimulation of the prothoracic gland by incubates of the corpus allatum and inhibition by incubates of the brain were demonstrated. An hypothesis is presented to account for these findings.

Deposition of insect cuticle in vitro: Differential responses to α- and β-ecdysone

Abstract A series of time-dose studies was made to study the effects of α- and β-ecdysone on the induction of cuticle deposition by leg regenerates of the cockroach Leucophaea maderae (F.). With β-ecdysone, similar contributions to the frequency of cuticle deposition were made by the concentration of and length of exposure to the hormone. The ability of α-ecdysone to induce cuticle deposition was time-dependent. Thus, the action of α-ecdysone required an additional rate-limited process that was not required for the action of β-ecdysone. Subsequent experiments showed that the action of α-ecdysone was inhibited by the presence of puromycin but that that of β-ecdysone was not. These findings indicate that the activity of α-ecdysone in inducing cuticle deposition in vitro is dependent on its enzymatic conversion to β-ecdysone. An overview of the literature suggests that these processes differ in tissues of insect from different orders.