We report on a phospholipase A2 (PLA2) found in the oral secretions, but not midgut contents, of ... more We report on a phospholipase A2 (PLA2) found in the oral secretions, but not midgut contents, of the burying beetle, Nicrophorus marginatus. PLA2 is responsible for hydrolyzing fatty acids from the sn-2 position of dietary phospholipids (PLs), an essential step in digestion and absorption of essential polyunsaturated fatty acids. Like the digestive PLA2s known from mammalian systems, and the one described insect digestive PLA2 the N. marginatus oral secretion PLA2 depends upon Ca2+ for full activity. However, unlike most digestive PLA2s, the N. marginatus enzyme is only partially inactivated in the absence of Ca2+. The PLA2 in N. marginatus oral secretions was influenced by altering the enzyme reaction conditions, including reaction time, protein concentration, pH, and temperature. Standard reaction conditions for assessing enzyme activity include 1.0 μg protein/μl incubated at pH 9.0 for 30 min at 28°C.
Sampling programs to establish baseline ecosystem information (e.g., species abundance and divers... more Sampling programs to establish baseline ecosystem information (e.g., species abundance and diversity) often fail to consider the potential influence of sampling techniques on results. Research on sampling economically important insects has demonstrated the possible influences of trap color and trap placement on results, but few data have been collected from natural environments. Consequently, we examined the effects of color (yellow and blue) and placement (exposed and shaded by plants) of sticky traps on insect captures and diversity estimates from a Nebraska inland salt marsh community. We identified 1913 specimens from 67 insect families collected during five trapping dates in July 1996. More Cicindelidae were collected on exposed traps, and more Staphylinidae, Dolichopodidae, Cicadellidae, and Thripidae were collected on shaded traps. More Dolichopodidae were collected on yellow traps, while more Syrphidae and Thripidae were collected on blue. Shannon and alpha diversity measures were significantly higher for shaded traps than exposed traps, but were not affected by trap color. Our results highlight the importance of characterizing sampling techniques when establishing diversity estimates. These data provide the first complete accounting of community-level insect response to colored sticky traps and provide new information for color preference of non-economic insect species.
Many amphipod crustaceans exhibit precopulatory mate guarding. Field samples of the amphipod Gamm... more Many amphipod crustaceans exhibit precopulatory mate guarding. Field samples of the amphipod Gammarus pseudolimnaeus indicated that pairs were positively size assortative. Receptive individuals readily formed pairs in the laboratory and the latency to formation of precopulatory pairs was decreased under threat of predation. In addition, females and, under conditions of extreme danger, males that formed pairs were significantly smaller when under the threat of predation. Amphipods distinguished between chemical stimuli (aquarium water) from predatory and nonpredatory fishes and between chemical cues from fish predators (trout) that had recently eaten conspecific amphipods vs. those fed a control diet of pelleted commercial fish food. These data indicate that chemical stimuli associated with predators can influence reproductive behavior of amphipods. The results also suggest the hypotheses that: 1. search time may be costly in terms of probability of predation; and 2. small pairs may be safer from predation than larger pairs.
1) Nodulation is the first, and qualitatively predominant, cellular defense reaction to bacterial... more 1) Nodulation is the first, and qualitatively predominant, cellular defense reaction to bacterial infections in insects and other invertebrates; 2) treating silkworms, Bombyx mori, with the eicosanoid biosynthesis inhibitor, dexamethasone, strongly reduced nodulation responses to bacterial infections; 3) the influence of dexamethasone was reversed by injecting the eicosanoid-precursor polyunsaturated fatty acid, arachidonic acid (20:4n-6), into dexamethasone-treated, infected larvae; 4) the presence of an eicosanoid biosynthesis system in silkworms was documented. Demonstrated elements include a digestive phospholipase A2, incorporation of exogenous 20:4n-6 into fat body phospholipids, the presence of 20:4n-6 in cellular phospholipids, a fat body intracellular phospholipase A2 that can hydrolyze 20:4n-6 from cellular phospolipids, and eicosanoid biosynthetic enzymes; and 5) these findings support the hypothesis that eicosanoids mediate cellular immune responses to bacterial infections in silkworms.
Nodulation is the first and quantitatively most important cellular defense reaction to bacterial ... more Nodulation is the first and quantitatively most important cellular defense reaction to bacterial infections in insects. Treating adults of the 17-year periodical cicadas, Magicicada septendecim and M. cassini, with eicosanoid biosynthesis inhibitors immediately prior to intrahemocoelic injections of the bacterium, Serratia marcescens, sharply reduced the nodulation response to bacterial challenges. Separate treatments with specific inhibitors of phospholipase A2, cyclooxygenase, and lipoxygenase reduced nodulation, supporting our view that nodule formation is a multi-step process in which individual steps are separately mediated by lipoxygenase and cyclooxygenase products. The inhibitory influence of dexamethasone was apparent by 2 h after injection, and nodulation was significantly reduced, relative to control insects, over the following 14 h. The dexamethasone effects were reversed by treating bacteria-challenged insects with the eicosanoid-precursor polyunsaturated fatty acid, arachidonic acid. Low levels of arachidonic acid were detected in fat body phospholipids. These findings in adults of an exopterygote insect species with an unusual life history pattern broaden our hypothesis that eicosanoids mediate cellular immune reactions to bacterial infections in most, if not all, insects.
Insects exhibit a remarkable array of adaptations that allow them to handle more or less severe h... more Insects exhibit a remarkable array of adaptations that allow them to handle more or less severe hypoxia associated with numerous aquatic and terrestrial habitats. We consider these habitats and then discuss physiological, behavioral and morphological mechanisms that facilitate insect life under oxygen deprivation. Actually or potentially hypoxic habitats include aquatic systems, flood-prone soils and burrows, intertidal zones, ice encasement and high altitudes. Some microhabitats, including dung, carrion, mammalian alimentary canals, grain and wood, also are subject to hypoxia. Adaptations to hypoxia include the ability to switch from aerobic to anaerobic metabolic pathways (with attendant generation of end products), the ability to drastically attenuate basal metabolic rates, altered behaviors and enlarged tracheal system volumes. Research into the biology of hypoxia seems to be progressing from early observations of the abilities of some insects to withstand exposure to hypoxia or anoxia through studies of organismal mechanisms operating in hypoxia to detailed investigations of cellular and intracellular signaling processes. Our hope is this essay will help crystallize the emergent picture of this area for those interested in contributing to future research.
We report on a phospholipase A2 (PLA2) found in the oral secretions, but not midgut contents, of ... more We report on a phospholipase A2 (PLA2) found in the oral secretions, but not midgut contents, of the burying beetle, Nicrophorus marginatus. PLA2 is responsible for hydrolyzing fatty acids from the sn-2 position of dietary phospholipids (PLs), an essential step in digestion and absorption of essential polyunsaturated fatty acids. Like the digestive PLA2s known from mammalian systems, and the one described insect digestive PLA2 the N. marginatus oral secretion PLA2 depends upon Ca2+ for full activity. However, unlike most digestive PLA2s, the N. marginatus enzyme is only partially inactivated in the absence of Ca2+. The PLA2 in N. marginatus oral secretions was influenced by altering the enzyme reaction conditions, including reaction time, protein concentration, pH, and temperature. Standard reaction conditions for assessing enzyme activity include 1.0 μg protein/μl incubated at pH 9.0 for 30 min at 28°C.
Sampling programs to establish baseline ecosystem information (e.g., species abundance and divers... more Sampling programs to establish baseline ecosystem information (e.g., species abundance and diversity) often fail to consider the potential influence of sampling techniques on results. Research on sampling economically important insects has demonstrated the possible influences of trap color and trap placement on results, but few data have been collected from natural environments. Consequently, we examined the effects of color (yellow and blue) and placement (exposed and shaded by plants) of sticky traps on insect captures and diversity estimates from a Nebraska inland salt marsh community. We identified 1913 specimens from 67 insect families collected during five trapping dates in July 1996. More Cicindelidae were collected on exposed traps, and more Staphylinidae, Dolichopodidae, Cicadellidae, and Thripidae were collected on shaded traps. More Dolichopodidae were collected on yellow traps, while more Syrphidae and Thripidae were collected on blue. Shannon and alpha diversity measures were significantly higher for shaded traps than exposed traps, but were not affected by trap color. Our results highlight the importance of characterizing sampling techniques when establishing diversity estimates. These data provide the first complete accounting of community-level insect response to colored sticky traps and provide new information for color preference of non-economic insect species.
Many amphipod crustaceans exhibit precopulatory mate guarding. Field samples of the amphipod Gamm... more Many amphipod crustaceans exhibit precopulatory mate guarding. Field samples of the amphipod Gammarus pseudolimnaeus indicated that pairs were positively size assortative. Receptive individuals readily formed pairs in the laboratory and the latency to formation of precopulatory pairs was decreased under threat of predation. In addition, females and, under conditions of extreme danger, males that formed pairs were significantly smaller when under the threat of predation. Amphipods distinguished between chemical stimuli (aquarium water) from predatory and nonpredatory fishes and between chemical cues from fish predators (trout) that had recently eaten conspecific amphipods vs. those fed a control diet of pelleted commercial fish food. These data indicate that chemical stimuli associated with predators can influence reproductive behavior of amphipods. The results also suggest the hypotheses that: 1. search time may be costly in terms of probability of predation; and 2. small pairs may be safer from predation than larger pairs.
1) Nodulation is the first, and qualitatively predominant, cellular defense reaction to bacterial... more 1) Nodulation is the first, and qualitatively predominant, cellular defense reaction to bacterial infections in insects and other invertebrates; 2) treating silkworms, Bombyx mori, with the eicosanoid biosynthesis inhibitor, dexamethasone, strongly reduced nodulation responses to bacterial infections; 3) the influence of dexamethasone was reversed by injecting the eicosanoid-precursor polyunsaturated fatty acid, arachidonic acid (20:4n-6), into dexamethasone-treated, infected larvae; 4) the presence of an eicosanoid biosynthesis system in silkworms was documented. Demonstrated elements include a digestive phospholipase A2, incorporation of exogenous 20:4n-6 into fat body phospholipids, the presence of 20:4n-6 in cellular phospholipids, a fat body intracellular phospholipase A2 that can hydrolyze 20:4n-6 from cellular phospolipids, and eicosanoid biosynthetic enzymes; and 5) these findings support the hypothesis that eicosanoids mediate cellular immune responses to bacterial infections in silkworms.
Nodulation is the first and quantitatively most important cellular defense reaction to bacterial ... more Nodulation is the first and quantitatively most important cellular defense reaction to bacterial infections in insects. Treating adults of the 17-year periodical cicadas, Magicicada septendecim and M. cassini, with eicosanoid biosynthesis inhibitors immediately prior to intrahemocoelic injections of the bacterium, Serratia marcescens, sharply reduced the nodulation response to bacterial challenges. Separate treatments with specific inhibitors of phospholipase A2, cyclooxygenase, and lipoxygenase reduced nodulation, supporting our view that nodule formation is a multi-step process in which individual steps are separately mediated by lipoxygenase and cyclooxygenase products. The inhibitory influence of dexamethasone was apparent by 2 h after injection, and nodulation was significantly reduced, relative to control insects, over the following 14 h. The dexamethasone effects were reversed by treating bacteria-challenged insects with the eicosanoid-precursor polyunsaturated fatty acid, arachidonic acid. Low levels of arachidonic acid were detected in fat body phospholipids. These findings in adults of an exopterygote insect species with an unusual life history pattern broaden our hypothesis that eicosanoids mediate cellular immune reactions to bacterial infections in most, if not all, insects.
Insects exhibit a remarkable array of adaptations that allow them to handle more or less severe h... more Insects exhibit a remarkable array of adaptations that allow them to handle more or less severe hypoxia associated with numerous aquatic and terrestrial habitats. We consider these habitats and then discuss physiological, behavioral and morphological mechanisms that facilitate insect life under oxygen deprivation. Actually or potentially hypoxic habitats include aquatic systems, flood-prone soils and burrows, intertidal zones, ice encasement and high altitudes. Some microhabitats, including dung, carrion, mammalian alimentary canals, grain and wood, also are subject to hypoxia. Adaptations to hypoxia include the ability to switch from aerobic to anaerobic metabolic pathways (with attendant generation of end products), the ability to drastically attenuate basal metabolic rates, altered behaviors and enlarged tracheal system volumes. Research into the biology of hypoxia seems to be progressing from early observations of the abilities of some insects to withstand exposure to hypoxia or anoxia through studies of organismal mechanisms operating in hypoxia to detailed investigations of cellular and intracellular signaling processes. Our hope is this essay will help crystallize the emergent picture of this area for those interested in contributing to future research.
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Papers by Wyatt W Hoback