Parallel somatotopic maps of gustatory and mechanosensory neurons in the central nervous system of an insect.

Relatively little is still known about the sense of taste, or contact chemoreception, compared with other sensory modalities, despite its importance to many aspects of animal behaviour. The central projections of the sensory neurons from bimodal contact chemoreceptors (basiconic sensilla) were compared with those from mechanosensory tactile hairs located on similar regions of the middle leg of the locust. Basiconic sensilla are multiply innervated, containing one mechanosensory and several chemosensory neurons, whereas tactile hairs are innervated by a single mechanosensory neuron. We show that the sensory neurons from tactile hairs form a complete 3-dimensional somatotopic map in the mesothoracic ganglion. Sensory neurons from hairs located on the coxa projected to a region near the midline of the ganglion with neurons from hairs located on progressively more distal parts of the leg arborizing in successively more lateral regions of neuropil. All the neurons from basiconic sensilla, both mechanosensory and chemosensory, also projected in a similar, strictly somatotopic, manner, and the arbors from these neurons overlapped considerably with those from tactile hairs on equivalent parts of the leg to form a continuous region. Thus, the position of a receptor on the leg is preserved in the central nervous system not only for the mechanosensory neurons from both tactile hairs and basiconic sensilla but also for chemosensory neurons. We could observe no anatomical features or small differences in projection region between sensory neurons from individual basiconic sensilla consistent with differences in modality.

The delayed effects and the basal follicle numbers developed by females of Culex pipiens L. Emerged from treatments of larvae with partially-lethal concentrations of Altosid and Dimilin.

The possible juvenilizing effects of Dimilin and Altosid against larvae of Culex pipiens L. were studied. Apart from delayed lethal action, possible effect on the mean number of basal follicles developed per female has been considered. A baseline exposure was found which caused only low mortalities of the early 4th larval instar. Results showed a correlation between the overall deaths during development and the sex ratio. Higher mortality increases the proportion of females. Treatments with 0.00001, 0.0001 and 0.001 ppm Dimilin caused 9.6%, 33.6% and 18.6% increase in the mean basal follicle numbers developed per female, respectively. In the case of Altosid, these levels of increase were 23.1%, 26.5% and 23.8%, respectively, after treatments with the same concentrations.

Effects of larval treatment with the insect development inhibitor PH60:40 on the vectorial capacity of Aedes aegypti (L.) for Brugia pahangi (Buckley and Edeson).

The effects of PH60:40, an insect development inhibitor, on fourth instar larvae of Aedes aegypti were investigated. Apart from delayed lethal action, possible effects on the vectorial capacity of Brugia pahangi were investigated. Two strains of A. aegypti were used, one DDT-susceptible and a good filarial vector and the other DDT-resistant and a refractory vector. A baseline exposure was found which caused only low mortalities in both strains. The treatments did not have any appreciable effect on the vectorial capacity of the good vector strain, but modified the refractory nature of the poor vector strain. It was considered possible that this could be due to a generalized harmful stress of the treatment rather than to a specific action of the chemical. Larvae were therefore subjected to heat treatments, as an example of stress, and these produced similar mortalities as with PH60:40. They did not. however, alter the vectorial capacity of survivors of either strain, so that the effects described do not seem to be due to simple stress.

Residue analysis of DDT, malathion and kelthane on pears.

Malthion, DDT, kelthane and their mixture (3 : 10 : 5) were applied to pear fruits at the rate recommended by the Ministry of Agriculture. The rate of disappearance of their residues on pear fruits was investigated under refrigerated conditions (2 +/- 1 degree and 47% relative humidity (RH)). The same insecticides were tested in higher concentrations (1.5 and 2 times) to determine the effect of insecticides on the black spots usually found on pears after storage. No relation was found between the tested insecticides and the appearance of the black spots. Residue-disappearance curves of the three tested concentrations of these insecticides and their mixture were drawn on semi-log paper. The residues of each material found on pear fruits after one hour, 1, 8, 15, 30 and 45 days' storage in a refrigerator, estimated biologically by C. pipiens larvae and D. magna were recorded. The highest concentrations of the mixture and of the individual insecticides left higher residues on pears than the lower ones of all the insecticides either as a mixture or alone. Stored pears, refrigerated under the above conditions immediately after treatment with the mixture of insecticides recommended for the pest control of pears, cannot be consumed fresh after 45 days.

Standard curves for nuvacron, malathion, sevin, DDT and kelthane tested against the mosquito Culex pipiens L. and the microcrustacean Daphnia magna Straus.

The fourth instar larvae of Culex pipiens L. and adults of microcrustacean Daphnia magna Straus were reared under standardized conditions and used as bioassay test organisms for the preparation of the standard log concentration--probit (lc--p) regression lines for each of the following pesticides: nuvacron, malathion, sevin, DDT and kelthane. When the above pesticides were tested against the larvae of C. pipiens, the LC50 values (in ppm) ranged as follows: nuvacron 0.0014--0.0019, malathion 0.0027-0.0043, sevin 0.059-0.095, DDT 0.233-0.525, kelthane 0.17-0.24 and a mixture of malathion, DDT and kelthane (3 : 10 : 5) 0.1805-0.2451, based on 24-h readings. The corresponding LC50 values (in ppm) for D. magna were 0.00018-0.00032, 0.000074-0.00013, 0.00063-0.00069, 0.0061-0.0064, 0.071-0.090 and 0.055-0.028 for the aforementioned pesticides. D. magna proved to be more sensitive to all tested pesticides than C. pipiens larvae: it succumbed to concentrations ranging from 0.000032 to 0.004 ppm of nuvacron, from 0.000032 to 0.0016 ppm of malathion, from 0.000032 to 0.02 ppm of sevin, from 0.0008 to 0.1 ppm of DDT, from 0.03 to 0.3 ppm of kelthane and from 0.007 to 0.075 ppm of the mixture. C. pipiens larvae were affected by concentrations ranging from 0.0005 to 0.008 ppm of of nuvacron, from 0.0005 to 0.04 ppm of malathion, from 0.008 to 1.0 ppm of sevin, from 0.05 to 2.5 ppm of DDT, from 0.06 to 0.5 ppm of kelthane and from 0.07 to 0.75 ppm of the mixture.

Effects of plant species, age and part on the disappearance of sevin, nuvacron and malathion residues.

Residues as determined by bioassay using Daphnia or mosquito larvae were in agreement with each other in most cases except sevin residues at 1 h and 8 days after treatment of mallow. The mosquito larvae failed to record nuvacron, sevin and malathion on 45-day-old plants on the 8th, 12th and 24th day, respectively, whereas residues on younger plants continued to affect mosquitoes up to the 12th day and disappeared only on the 24th day. Daphnia continued to show toxicity up to the 24th day on younger and older plants. Insecticide residues of nuvacron, malathion and sevin, found on the leaves 30- and 45-day-old plants of cotton, Jew's mallow and kidney beans after 1 h, 1, 4, 8, 12 and 24 days were estimated biologically by C. pipiens larvae and D. magna. Residues of insecticides disappeared more readily on bean pods than on bean leaves. Residues of sevin, malathion and nuvacron found on the pods 12 days after treatment as indicated by Daphnia were 0.189, 0.055 and 0.059 ppm respectively. They are far less than the corresponding residues on bean leaves. The 1-hour residue was higher on younger bean leaves than on mallow and cotton with very few exceptions (nuvacron, malathion and sevin: 2.125, 11.75 and 95 ppm on cotton leaves; 2.25 and 145 ppm on Jew's mallow and 3.750, 32.500 and 250 ppm on common bean leaves, respectively). These data were obtained with C. pipiens larvae. The picture was completely reversed on 45-day-old plants. 1-h deposits of malathion were higher on mallow than on cotton or beans (nuvacron, malathion and sevin; 2.3, 200 and 140 ppm on cotton leaves, 1.90, 191.15 and 92.86 ppm on mallow leaves, 2.25, 21.5 and 137.5 ppm on common bean leaves, respectively). These data were obtained with C. pipiens larvae. Nuvacron residues on 45-day-old mallow were less on mallow than on cotton or beans. Sevin was higher in 1-h residues on cotton and beans than on mallow. Mallow did not retain insecticides as long as did cotton and beans. The initial concentration of nuvacron was little less than that of sevin and malathion. It was more toxic to mosquito larva (LC50 = 0.0016 ppm) than malathion (LC50 = 0.0034 ppm) and sevin (LC50 = 0.075 ppm). Daphnia was more affected by malathion (LC50 = 0.000098 ppm) than by nuvacron (LC50 = 0.00024 ppm). Nuvacron was nearly equitoxic to sevin (LC50 = 0.00026 ppm) against Daphnia. In spite of this all tested plants, both young or older ones, retained nuvacron in the smallest quantities in proportion to the other insecticides. The 1-h residues were less on older plants (except cotton) for only nuvacron and sevin: 2 and 94.5, 1.9 and 92.8 ppm than on younger ones 2.4 and 137.2, 2.25 and 145 ppm as indicated by Daphnia and mosquito larvae respectively. This emphasizes that the initial concentration is not the limiting factor for the determination of the 1-h residue as the initial concentration was much higher on older than on younger plants.