Responses in insects

By understanding this it may be readily appreciated that the toxicological findings in rats and mice are indeed predictable and, because of a differing response in insects, humans are protected by a wide margin of safety. This has of course been borne out in practice by a very long history of safe use, encompassing the last 40 years or so. 

Much evidence has accumulated that octopamine functions as a neurotransmitter, neurohormone and neuromodulator in insects (for reviews see 1JL, 12 ). The physiological events influenced by octopamine are those that might be expected to be associated with a generalized sympathetic response and indeed, octopamine has been proposed as the mediator of a sympathomimetic response in insects. 

Hetru, C., Hoffmann, D., Bulet, P. Antimicrobial peptides from insects. In Molecular mechanisms of immune responses in insects Brey P.T. and Hultmark, D. (Eds.) Chapman Hall New York, 1998 pp. 44—66... 

The first studies in this direction, which were started by Clever (1961), led to some very interesting results. Clever carried out experiments to study the effect of the hormone ecdysone, responsible in insects for induction of the metamorphosis from larva to pupa (a hormone of steroid type) on the pattern and activity of puffs. This hormone is produced by the pro thoracic gland. 

Provides a coordinated crop protection industry response to the development of resistance in insect and mite pests. During the last decade, IRAC has formed several international working gi oups to provide practical solutions to mite and insect resistance problems within major crops and pesticide groups. 

Materials produced by crystalliferous bacilli which elicit a toxic response in susceptible insects may be separated into two types. The first type, the true toxins, include the crystalline protein inclusion body the parasporal body of Hannay (14)], a heat-stable, water-soluble exotoxin active against flies, a heat-stable, dialyzable water-soluble exotoxin, toxic to Lepidoptera on injection (23), and a heat-labile, water-soluble, filterable exotoxin, toxic toward larch sawfly larvae (Hymenoptera) which was reported by Smirnoff (31). 

Water-Soluble Exotoxins. In this area, we enter into the slightly muddy waters of the lower molecular weight compounds which elicit toxic responses in susceptible host insects. Without reference to molecular identity, it is possible to sift through the various reports on the effects of bacillus-produced soluble exotoxins and recognize three possible types of material which are produced under appropriate conditions by specific strains of bacilli ... 

The organophosphorons insecticides dimethoate and diazinon are mnch more toxic to insects (e.g., housefly) than they are to the rat or other mammals. A major factor responsible for this is rapid detoxication of the active oxon forms of these insecticides by A-esterases of mammals. Insects in general appear to have no A-esterase activity or, at best, low A-esterase activity (some earlier stndies confnsed A-esterase activity with B-esterase activity) (Walker 1994b). Diazinon also shows marked selectivity between birds and mammals, which has been explained on the gronnds of rapid detoxication by A-esterase in mammals, an activity that is absent from the blood of most species of birds (see Section 23.23). The related OP insecticides pirimiphos methyl and pirimiphos ethyl show similar selectivity between birds and mammals. Pyrethroid insecticides are highly selective between insects and mammals, and this has been attributed to faster metabolic detoxication by mammals and greater sensitivity of target (Na+ channel) in insects. 

At its most fundamental level, the circadian cycle rests on the influence of so-called clock genes . These genes have been studied most extensively in insects but they have also been found in humans. Their protein products enter the cell nucleus and regulate their own transcription. This feedback process is linked to exposure to light and so it is not surprising that visual inputs are important for maintenance of circadian rhythms. However, it is not the reception of specific visual information, transmitted in the optic nerve to the lateral geniculate nucleus (LGN) and visual cortex (i.e. visual discrimination), that is responsible for the rhythm but the more simple, almost subconscious, reception of light. 

Drosophila bristle receptors and chordotonal organs are surface mechanoreceptors. These surface mechanoreceptors on insects have been studied for many years. Progress on identifying molecules responsible for insect mechanoreception received a big boost in 1994, when Kernan et al. developed a screen for mechanoreceptor mutants in Drosophila [5], They identified several dozen mutants that were deficient in mechanoreception and, with the assistance of their colleagues, have begun to identify them. 

The sex pheromone communication system basically involves the release of specific chemicals from a pheromone producer (emitter), the transmission of these chemicals in the environment to a receiver, and the processing of these signals to mediate appropriate behavioral responses in the receiver. The chemicals transmitted downwind have been the most obvious targets for characterization. The code was first broken with the publication in 1959 (3) of the sex pheromone for the domesticated silkworm Bombyx mori after extraction of a half million female silkworm pheromone glands and 30 years of classical chemical analyses. The pheromone was found to be (E10, Z12)-hexadecadien-l-ol, which was called bombykol. This work showed that there was nothing magical about the communication system, and chemists around the world were "attracted" to this area of research on insect pheromones. 

Karsten U, Franklin LA, Liming K, Wiencke C (1998) Natural ultraviolet radiation and photosyn-thetically active radiation induce formation of mycosporine-like amino acids in the marine macroalga Chondrus crispus (Rhodophyta). Planta 205 257-262 Karsten U, Bischof K, Hanelt D, Tug H, Wiencke C (1999) The effect of ultraviolet radiation on photosynthesis and ultraviolet-absorbing substances in the endemic Arctic macroalga Devaleraea ramentacea (Rhodophyta). Physiol Plant 105 58-66 Kessler A, Baldwin IT (2002) Plant responses to insect herbivory the emerging molecular analysis. Ann Rev Plant Biol 53 299-328... 

Interferences in the mussel homogenates may be responsible, in part at least, for the low measured epoxidation activity. Properties of endogenous inhibitors in several insect preparations have been reviewed by Wilkinson and Brattsten (29). 

Carboxylesterases are well-represented in insects and are sometimes important in the development of resistance to insecticides. Thus, a well-characterized carboxylesterase E4 is responsible for resistance to organophosphorus insecticides in the aphid (Myzuspersicae) [107]. In the California Culex mosquito, the esterase B1 is 500-fold more abundant in organophosphate-resistant than in susceptible insects. The increase of esterase levels is the result of gene amplification, i.e., the resistant animals have an increased number of copies of the structural esterase gene [108],... 

Karlson and Luscher first introduced the term pheromone in 1959 in a publication about chemical communication in insects in the scientific journal NatureP A pheromone was viewed as a substance that is secreted or excreted into the environment by one individual that elicits some behavioral, developmental, or endocrine response when received by another individual of the same species. The behavioral change in the male silkworm moth in response to bombykol secreted into the environment by the female of the same species fits this mold, for example. 

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