The slow growth-high mortality hypothesis （SG-HG） predicts that slower growing herbivores suffer greater mortality due to a prolonged window of vulnerability. Given diverse plant-herbivore-natural enemy systems resu...The slow growth-high mortality hypothesis （SG-HG） predicts that slower growing herbivores suffer greater mortality due to a prolonged window of vulnerability. Given diverse plant-herbivore-natural enemy systems resulting from different feeding ecologies of herbivores and natural enemies, this hypothesis might not always be applicable to all systems. This is evidenced by mixed support from empirical data. In this study, a meta- analysis of the SG-HM hypothesis for insects was conducted, aiming to find conditions that favor or reject SG-HM. The analysis revealed significant within- and between-group heterogeneity for almost a11 explanatory variables and overall did not support SG-HM. In this analysis, SG-HM was supported when any of the following 5 conditions was met： （1） host food consisted of artificial diet; （2） herbivore growth was measured as larval mass; （3） herbivores were generalists; （4） no or multiple species of natural enemies were involved in the study; and （5） parasitoids （i.e., parasitic insects） involved in the study were gregarious. SG-HM was rejected when any of the following 5 conditions was met： （1） herbivores were from the order Hymentoptera; （2） parasitoids from more than 1 order caused herbivore mortality; （2） parasitoids were specialists; （3） parasitoids were solitary; （4） parasitoids were idiobionts or koinobionts; and （5） single species of natural enemy caused mortality of specialist herbivores. All known studies investigated herbivore mortality for a short period of their life cycle. Researchers are encouraged to monitor herbivore mortality during the entire window of susceptibility or life cycle using life tables. Studies involving multiple mortality factors （i.e., both biotic and abiotic） or multiple natural enemy species are also encouraged since herbivores in nature face a multitude of risks during the entire life cycle. More comprehensive studies may increase our understanding of factors influencing the relationships between herbivore growth and mortality.展开更多
The polyphagous shot hole borer （PSHB）, Euwallacea sp., was first detected in 2003 in Los Angeles County, California, USA. Recently, this invasive species has become a major pest of many hardwood trees in urban and ...The polyphagous shot hole borer （PSHB）, Euwallacea sp., was first detected in 2003 in Los Angeles County, California, USA. Recently, this invasive species has become a major pest of many hardwood trees in urban and wildland forests throughout southern California. PSHB is nearly identical in morphology and life history to the tea shot hole borer （TSHB）, Euwallaceafornicatus, an invasive pest of hardwoods in Florida, USA and many other parts of the world. However, molecular studies have suggested that the taxa are different species. We conducted morphometric and chemical analyses of the pheno- types of Euwallacea sp. collected in southern California （Los Angeles County） and E. fornicatus collected in Florida （Miami-Dade County）. Our analyses indicated that PSHB has 3 larval instars. The third larval instar was separated from the first 2 instars by head capsule width with 0 probability of misclassification. The body length, head width, and pronotal width of PSHB adult males were significantly less than those of females. Head width and pronotal width of female PSHB were significantly less than those of female TSHB. In contrast, body length, and ratio of body length to pronotal width of female PSHB were significantly greater than those of female TSHB. However, females of these 2 species could not be separated completely by these 4 measurements because of the overlapping ranges. Cuticular hydrocarbons detected in both species were exclusively alkanes （i.e., n-alkanes, monomethylalkanes, dimethylalkanes, and trimethylalkanes）. Cuticular hydro- carbon profiles of PSHB males and females were similar, but they both differed from that of TSHB females. Cuticular hydrocarbons of PSHB were predominantly internally branched dimethylalkanes with backbones of 31 and 33 carbons, whereas cuticular hydro- carbons of TSHB females were dominated by internally branched monomethylalkanes and dimethylalkanes with backbones of 28 and 29 carbons. Multiple compounds within these classes appear to be diagnostic for PSHB and TSHB, respectively.展开更多
Many natural enemies employ plant- and/or herbivore-derived signals for host/prey location. The larval parasitoid Tetrastichus planipennisi Yang （Hymenoptera： Eulophidae） is 1 of 3 biocontrol agents currently being...Many natural enemies employ plant- and/or herbivore-derived signals for host/prey location. The larval parasitoid Tetrastichus planipennisi Yang （Hymenoptera： Eulophidae） is 1 of 3 biocontrol agents currently being released in an effort to control the emerald ash borer （EAB）, Agrilus planipennis Fairmaire （Coloeptera： Burprestidae） in North America. To enhance its efficiency, allelochemicals that attract it need to be assessed. In this study, ash phloem volatile organic compounds （VOCs） of black, green, and white ash, and EAB larval frass were compared. Foraging behavior of T. planipennisi females in response to VOCs of white ash or frass from EAB larvae feeding on white ash phloem was tested using a Y-tube olfactometer. Results indicated that the 3 ash species had similar VOC profiles. EAB larval frass generally contained greater levels of VOCs than phloem. Factor analysis indicated that the 11 VOCs could be broadly divided into 2 groups, with c^-bisabolol, fl-caryophyllene, （E）-2-hexenal, （Z）-3-hexenal, limonene, methyl benzoate, methyl indole-3-acetic acid, methyl jasmonate, methyl salicylate as the first group and the rest （i.e., methyl linoleate and methyl linolenate） as a second. Abundance of VOCs in white ash phloem tissue and frass, nevertheless, did not attract T. planipennisi females. The concealed feeding of EAB larvae might explain the selection for detectable and reliable virbrational signals, instead of undetectable and relatively unreliable VOC cues from phloem and frass, in short-range foraging by T. planipennisi. Alternatively, it is possible that T. planipennisi is not amenable to the Y-tube olfactometer assay employed.展开更多
文摘The slow growth-high mortality hypothesis （SG-HG） predicts that slower growing herbivores suffer greater mortality due to a prolonged window of vulnerability. Given diverse plant-herbivore-natural enemy systems resulting from different feeding ecologies of herbivores and natural enemies, this hypothesis might not always be applicable to all systems. This is evidenced by mixed support from empirical data. In this study, a meta- analysis of the SG-HM hypothesis for insects was conducted, aiming to find conditions that favor or reject SG-HM. The analysis revealed significant within- and between-group heterogeneity for almost a11 explanatory variables and overall did not support SG-HM. In this analysis, SG-HM was supported when any of the following 5 conditions was met： （1） host food consisted of artificial diet; （2） herbivore growth was measured as larval mass; （3） herbivores were generalists; （4） no or multiple species of natural enemies were involved in the study; and （5） parasitoids （i.e., parasitic insects） involved in the study were gregarious. SG-HM was rejected when any of the following 5 conditions was met： （1） herbivores were from the order Hymentoptera; （2） parasitoids from more than 1 order caused herbivore mortality; （2） parasitoids were specialists; （3） parasitoids were solitary; （4） parasitoids were idiobionts or koinobionts; and （5） single species of natural enemy caused mortality of specialist herbivores. All known studies investigated herbivore mortality for a short period of their life cycle. Researchers are encouraged to monitor herbivore mortality during the entire window of susceptibility or life cycle using life tables. Studies involving multiple mortality factors （i.e., both biotic and abiotic） or multiple natural enemy species are also encouraged since herbivores in nature face a multitude of risks during the entire life cycle. More comprehensive studies may increase our understanding of factors influencing the relationships between herbivore growth and mortality.
文摘The polyphagous shot hole borer （PSHB）, Euwallacea sp., was first detected in 2003 in Los Angeles County, California, USA. Recently, this invasive species has become a major pest of many hardwood trees in urban and wildland forests throughout southern California. PSHB is nearly identical in morphology and life history to the tea shot hole borer （TSHB）, Euwallaceafornicatus, an invasive pest of hardwoods in Florida, USA and many other parts of the world. However, molecular studies have suggested that the taxa are different species. We conducted morphometric and chemical analyses of the pheno- types of Euwallacea sp. collected in southern California （Los Angeles County） and E. fornicatus collected in Florida （Miami-Dade County）. Our analyses indicated that PSHB has 3 larval instars. The third larval instar was separated from the first 2 instars by head capsule width with 0 probability of misclassification. The body length, head width, and pronotal width of PSHB adult males were significantly less than those of females. Head width and pronotal width of female PSHB were significantly less than those of female TSHB. In contrast, body length, and ratio of body length to pronotal width of female PSHB were significantly greater than those of female TSHB. However, females of these 2 species could not be separated completely by these 4 measurements because of the overlapping ranges. Cuticular hydrocarbons detected in both species were exclusively alkanes （i.e., n-alkanes, monomethylalkanes, dimethylalkanes, and trimethylalkanes）. Cuticular hydro- carbon profiles of PSHB males and females were similar, but they both differed from that of TSHB females. Cuticular hydrocarbons of PSHB were predominantly internally branched dimethylalkanes with backbones of 31 and 33 carbons, whereas cuticular hydro- carbons of TSHB females were dominated by internally branched monomethylalkanes and dimethylalkanes with backbones of 28 and 29 carbons. Multiple compounds within these classes appear to be diagnostic for PSHB and TSHB, respectively.
文摘Many natural enemies employ plant- and/or herbivore-derived signals for host/prey location. The larval parasitoid Tetrastichus planipennisi Yang （Hymenoptera： Eulophidae） is 1 of 3 biocontrol agents currently being released in an effort to control the emerald ash borer （EAB）, Agrilus planipennis Fairmaire （Coloeptera： Burprestidae） in North America. To enhance its efficiency, allelochemicals that attract it need to be assessed. In this study, ash phloem volatile organic compounds （VOCs） of black, green, and white ash, and EAB larval frass were compared. Foraging behavior of T. planipennisi females in response to VOCs of white ash or frass from EAB larvae feeding on white ash phloem was tested using a Y-tube olfactometer. Results indicated that the 3 ash species had similar VOC profiles. EAB larval frass generally contained greater levels of VOCs than phloem. Factor analysis indicated that the 11 VOCs could be broadly divided into 2 groups, with c^-bisabolol, fl-caryophyllene, （E）-2-hexenal, （Z）-3-hexenal, limonene, methyl benzoate, methyl indole-3-acetic acid, methyl jasmonate, methyl salicylate as the first group and the rest （i.e., methyl linoleate and methyl linolenate） as a second. Abundance of VOCs in white ash phloem tissue and frass, nevertheless, did not attract T. planipennisi females. The concealed feeding of EAB larvae might explain the selection for detectable and reliable virbrational signals, instead of undetectable and relatively unreliable VOC cues from phloem and frass, in short-range foraging by T. planipennisi. Alternatively, it is possible that T. planipennisi is not amenable to the Y-tube olfactometer assay employed.
