Laboratory studies on the acute contact and oral toxicities of insecticides to honeybees

Standard procedures for determining acute oral and contact toxicities of insecticides to worker honeybees were developed and used to find the median lethal doses (LD₅₀) of twenty-one compounds. The test procedures can be simplified to give less precise results and can be applied with little modification to other species of bee.     

The secretion of the systemic insecticides dimethoate and phorate into nectar

In pot experiments, root applications of dimethoate and phorate were made to plants of fuchsia, nasturtium and bean. Twenty-five mg dimethoate applied to a 5-in pot made nectar from fuchsia and nasturtium and nectaries of beans toxic to bees and Drosophila melanogaster. Similar amounts of phorate and disulfoton did not cause toxicity. Gas chromatography showed that 4 days after treatment there was at least 100 times more dimethoate than phorate in the nectar of fuchsia and nasturtium. The dimethoate in nectaries taken from bean plants treated at rates between 0·5 and 50 mg dimethoate per pot was assayed by gas chromatography. The concentration of dimethoate in the nectaries depended on the applied dose: it was greatest 4 days after treatment. Loss was more rapid with larger doses than with smaller doses.     

Changing Activities of the Crustacean Epidermis during the Molting Cycle

The criteria established by Drach for subdividing the moltingcycle into stages are reviewed, and a suggestion is made forimproving the uniformity of postmolt staging of different species.Changes in the epidermis during the molting cycle of the crayfishOrconectes obscurus and O. sanborni are described. EpidermalDNA content was measured throughout the cycle and found to dropsharply at stage D₀ and to rise sharply at stage A. Proteincontent declined during postmolt and rose during premolt, asexpected. Protein synthesis remained more or less constant duringpostmolt, rose during premolt, and dropped to the postmolt levelat ecdysis. Chitin synthesis appeared to follow two differentcurves depending upon whether labelled glucose or acetylglucosaminewas used as precursor. This, and the presence of a separateenzyme capable of phosphorylating acetylglucosamine and notglucose, suggests that acetylglucosamine may be utilized directlywithout prior conversion to glucose. Actinomycin D was foundto prevent increases in rate of chitin biosynthesis during premoltbut not to inhibit chitin biosynthesis already underway. Duringthe same period, actinomycin stimulated general protein biosynthesis.By utilizing the molt staging criteria described, we were ableto detect induction of premolt by ecdysone.     

Isoforms of glutamine synthetase in asparagus spears: the cytosolic enzyme increases after harvest

Two distinct forms of glutamine synthetase (GS) have been identified in the spear tip tissues of harvested asparagus (Asparagus officinalis L. cv. Limbras 10). The GS activities were separated by anion exchange chromatography. They have distinct kinetic properties and contain polypeptides of different sizes, and the abundances of the GS isoforms change differently after harvest. Plastid GS has a 44 kD polypeptide, and during the post-harvest period the abundance of this polypeptide declined dramatically. After 5 d, the activity of plastid GS had declined to just 20% of that at harvest. Cytosolic GS has a 40 kD polypeptide and is the major constituent of the GS activity present at harvest (73% of total). After harvest, cytosolic GS activity declined by half and then, at 3 or 4 d after harvest, rose to 80% of the cytosolic GS activity present at harvest. The nitrogen metabolism of asparagus spears is significantly altered as the tissues deteriorate rapidly after harvest. We demonstrate that cytosolic GS activity increases during the post-harvest period and is likely to be a critical feature of the physiology of the tip of a harvested asparagus spear.     

The toxicity to foraging honeybees, Apis mellifera, of endosulfan, malathion and azinphos-methyl applied to flowering oil seed rape, Brassica napus

Wettable powder and emulsifiable concentrate formulations of endosulfan and azinphos-methyl and an emulsifiable concentrate of malathion were sprayed on oil seed rape in full flower to assess their relative toxicities to foraging honeybees. Endosulfan was very much safer to honeybees than the two organophosphate insecticides, but there was little difference between the two types of formulation.