Ralph E. Berry

Host plant stimulation of detoxifying enzymes in a phytophagous insect

Abstract The midgut microsomal aldrin epoxidase of variegated cutworm larvae (Peridroma saucia, Hubner) fed bean or peppermint leaves was up to 10 and 45 times more active, respectively, than that of larvae fed a basic control diet. Large increases in oxidase activity and cytochrome P-450 levels also occurred in larvae fed mint plant constituents such as menthol menthone, α-pinene, and β-pinene. Mint-fed larvae were more tolerant of the insecticide, carbaryl, than bean-fed larvae.

Longevity of phytophagous heteropteran predators feeding on transgenic Btt‐potato plants

As public opposition to insecticide use increases due to human and environmental health concerns, alternative methods for controlling agricultural pests must be found in order to maintain adequately high crop yields. One such method is the use of the bacterium Bacillus thuringiensis(Bt) and its toxin that, when ingested by an appropriate host insect, binds to the brush-border of the insect’s gut and increases gut cell water permeability. The midgut epithelium cells swell and lyse, leading to bacterial septicemia and host death (Slaney et al., 1992). In the last decade, researchers have isolated theδ-endotoxin toxin gene from different strains of Bt, and have expressed the gene in corn, cotton, poplar trees, tobacco, potatoes, and eggplant to control lepidopteran and coleopteran pests. Potato plants have been transformed with the CryIIIA δ-endotoxin gene ofBacillus thuringiensis ubsp.tenebrionis(Btt) (Perlak et al., 1993) to control the Colorado potato beetle, one of the most serious insect pests of potatoes in the United States and Europe. This insect costs U.S. potato growers approximately

Phylogeny of Photorhabdus and Xenorhabdus species and strains as determined by comparison of partial 16S rRNA gene sequences

100 million annually to control (Perlak et al., 1993) and has developed resistance to most available pesticides (Ferro, 1994), making it an ideal target for alternate methods of control. Proponents of planting transgenic crops suggest that the use of toxin-expressing transgenic plants could permit fewer pesticide applications, which would allow natural enemies to survive and provide control of pest insects not affected by the transgenic gene products (Perlak et al., 1993). Colorado potato beetle is not the only pest of potato crops; aphids, loopers and cutworms, spider mites, and psyllids also are occasional or frequent pests that are not controlled by the CryIIIA endotoxin. Natural enemies including coccinellids, carabids, lacewings, and several heteropteran generalist predators feed on many of these potato pests (Hough-Goldstein et al., 1993; Hilbeck & Kennedy, 1996). These predators are frequently killed by the application of pesticides (Hilbeck & Kennedy, 1996), but if pesticide sprays are reduced by the use of transgenic plants, the predators can survive to control pest arthropods not affected by the Btt toxin. However, if the Btt toxin adversely affects predators, the natural enemies cannot provide control of pests remaining on the plants. A key group of predators, members of the Heteroptera, feeds directly on plants for nutrients and moisture to supplement their prey diet (Naranjo & Gibson, 1996; Coll, 1998). Several heteropteran predators feed on the mesophyll of leaves (Cohen, 1990; Armer et al., 1998), where high levels of Btt toxin are expressed ( ∼0.1% of total leaf proteins, [Perlak et al., 1993]). Therefore, these predators would encounter high concentrations of toxin when feeding on transgenic plants. This study examines the effect of direct feeding on transgenic Btt potato plants on the longevity of plant-feeding predatory Heteroptera.

Aldrin epoxidase activity and cytochrome P-450 content of microsomes prepared from alfalfa and cabbage looper larvae fed various plant diets

Partial 16S rRNA gene sequences of 16 strains of the genera Photorhabdus and Xenorhabdus were determined by direct sequencing of PCR products. Aligned sequences were subjected to phylogenetic analysis by maximum-likelihood and maximum-parsimony methods. Distance matrix and phylogenetic analysis did not separate the genera unambiguously. Taxonomic grouping of the bacteria closely paralleled taxonomic grouping of their nematode associates and their geographic origins. We found at least two well-supported taxonomic groups in Photorhabdus species, which suggests that the genus Photorhabdus is coevolving with the nematodes and may be polyspecific.

Molecular differentiation and phylogeny of entomopathogenic nematodes (rhabditida: heterorhabditidae) based on ND4 gene sequences of Mitochondrial DNA.

Abstract The alfalfa looper ( Californica autographica ) and the cabbage looper ( Trichoplusia ni ) were reared through the fourth instar on a semidefined artificial diet and for the first 60 hr of the last instar on fresh leaves of one of their host plants. Microsomes prepared from midguts and a carcass segment which included the fat body were then assayed for aldrin epoxidase activity and cytochrome P -450 content. Epoxidation by midgut microsomes of alfalfa loopers fed peppermint leaves was at a rate up to eight times that of larvae fed alfalfa, snap beans, or broccoli. The epoxidase activity of the carcass microsomes was induced about fourfold by the peppermint diet. Midgut microsomes prepared from cabbage looper larvae reared on peppermint leaves were also more active (about four times) than those reared on alfalfa, broccoli, or cabbage. Although the epoxidase activity of the carcass microsomes of the cabbage loopers was low, about one-eighth that of the midgut microsomes, this enzyme was greatly induced by peppermint leaves. In neither species did the peppermint leaf diet cause a corresponding increase in the cytochrome P -450 content of the microsomes, the maximum difference between peppermint and the other plants being about twofold. Bioassays of cabbage looper larvae reared on broccoli or peppermint and of alfalfa loopers reared on alfalfa or peppermint indicated that the stimulation of microsomal oxidase activity by the peppermint constituents provided increased tolerance for carbaryl and methomyl but not acephate.

Colorado potato beetle control by application of the entomopathogenic nematode Heterorhabditis marelata and potato plant alkaloid manipulation

We determined partial ND4 gene sequences of mitochondrial DNA from 15 heterorhabditid nematode isolates, representing 5 species collected from different regions of the world, by using polymerase chain reaction (PCR) and direct-sequencing of PCR products. Aligned nucleotide as well as amino acid sequences were used to differentiate nematode species by comparing sequence divergence and to infer phylogeny of the nematodes by using maximum parsimony and likelihood methods. Robustness of our phylogenetic trees was checked by bootstrap tests. The 15 nematode isolates can be divided into 7 haplotypes based on DNA sequences. On a larger scale, the sequence divergence revealed 4 distinct groups corresponding to 4 described species. No sequence divergence was detected from 5 isolates of Heterorhabditis bacteriophora or between Heterorhabditis marelatus to Heterorhabditis hepialius. Our sequence data yielded phylogenetic trees with identical topologies when different tree-building methods were used. Most relationships were also confirmed by using amino acid sequences in maximum parsimony analysis. Our molecular phylogeny of Heterorhabditis species support an existing taxonomy that is based largely on morphology and the sequence divergence of the ND4 gene permits species identification.

Effects of nitrogen and Douglas-fir allelochemicals on development of the gypsy moth,Lymantria dispar

Control of the Colorado potato beetle (CPB), Leptinotarsa decemlineata (Say) (Coleoptera: Chrysomelidae), with the entomopathogenic nematode Heterorhabditis marelata Liu and Berry (Nematoda: Heterorhabditidae) was examined in the laboratory and in potato fields in north central Oregon. This research tested the hypothesis that varying nitrogen fertilizer levels would affect foliar alkaloid levels, which would stress the host, and allow increased nematode reproduction and long‐term control of the CPB. Laboratory results indicated that nematodes tended to reproduce more readily in CPB fed on potato plants with high levels of fertilizer. Field trials tested CPB population responses to four treatments: application of nematodes vs. no nematodes, with application of low vs. high rates of nitrogen fertilizer. The higher nitrogen application rate increased field foliar levels of the alkaloids solanine by 35%, and chaconine by 41% over the season. Nematodes were applied twice during the season, causing a 50% reduction in adult CPB populations, and producing six times as many dead prepupae in nematode‐treated soil samples as in the untreated samples. However, no reproducing nematodes were found in the 303 dead prepupae and pupae collected from nematode‐treated plots. Nitrogen fertilizer levels, and their related alkaloid levels, did not affect nematode infection rates or reproduction in the field. Foliar alkaloid levels of plants from the growth chamber were 3–6‐fold as high as those in the field, which may explain the variation in nematode response to nitrogen applications to host plants of the CPB. Heterorhabditis marelata is effective for controlling CPB in the field, and does not have negative non‐target effects on one of the most common endemic CPB control agents, Myiopharus doryphorae (Riley) (Diptera: Tachinidae), but the low rate of nematode reproduction cannot be manipulated through alkaloid stress to the beetle. Until H. marelata can be mass‐produced in an inexpensive manner, it will not be a commercially viable control for CPB.

Cytochrome P-450 in insects—V.: Monoterpene induction of cytochrome P-450 and associated monooxygenase activities in the larva of the variegated cutworm Peridroma saucia (Hübner)☆

Two experiments were conducted to examine the influence of foliar nitrogen, terpenes, and phenolics of Douglas-fir on the development of gypsy moth larvae. In the first experiment, foliar concentrations of nitrogen and allelochemicals were manipulated by fertilizing 3-year-old potted seedlings with 0 or 200 ppm nitrogen. Concentrations of foliar nitrogen (0.33–2.38%) were negatively correlated with the phenolics (15.8–24.4 mg/g). Sixth-instar larvae previously reared on current-year Douglas-fir needles were allowed to feed on these seedlings. Pupal weights (312.8–995.6 mg) were positively correlated with levels of foliar nitrogen, negatively correlated with amounts of foliar phenolics, and uncorrelated with terpene concentrations. In the second experiment, terpene and phenolic extracts from Douglas-fir foliage were incorporated at natural levels into artificial diets with high and low levels of protein nitrogen. Neonate larvae grew faster and were larger on the high nitrogen control diet (4.1–4.5%), however, fourth instars performed better on the control diet with low nitrogen levels (2.5–2.7%). Foliar terpenes incorporated into diet had little effect on neonate fitness, but may induce subtle physiological changes in later instar larvae. Phenolics, alone or in combination with terpenes, excessively suppressed growth and survival, with no individuals living through the fourth instar, regardless of the nitrogen level. Incorporating foliar phenolic extracts into artificial diet caused unnatural levels of toxicity and failed to clarify the effects of Douglas-fir phenolics on gypsy moth fitness. Foliar nitrogen is a key factor influencing gypsy moth development on Douglas fir, but may be mitigated to some degree by phenolics.

White alder and Douglas-fir foliage quality and interegg-mass influences on larval development of gypsy moth,Lymantria dispar.

Abstract 1. The induction of microsomal cytochrome P-450 and associated polysubstrate monoxygenase activities by natural levels (0.01–0.1%) of the naturally occurring monoterpenes pulegone, menthone and menthol was examined in sixth-instar larvae of the variegated cutworm ( Peridroma saucia Hubner). 2. The monoterpenes increased cytochrome P-450 levels, aldrin and heptachlor epoxidase activity in microsomes from midgut and other tissues of the midsection. 3. NADPH-dependent cytochrome c reductase levels generally were not increased in midgut microsomes and were increased in carcass microsomes by higher doses of the inducers. 4. Induction by any of the monoterpenes increased the size of the Type I (substrate) binding spectra obtained with pulegone, menthone and nerolidol, but not those obtained with menthol. 5. The induction of polysubstrate monooxygenases by these compounds may increase the resistance of the larvae to both host plant allelochemicals and to insecticides in the field.

Fall Flaming Effects on Densities, Distributions, and Dispersal of Tetranychus urticae and Neoseiulus fallacis (Acari: Tetranychidae, Phytoseiidae) on Peppermint

Individual families of gypsy moth collected from a single population exhibited different degrees of fitness when fed diets of white alder, a suitable broadleaf host, and Douglas-fir, an unsuitable conifer host. Members of families on diets of Douglas-fir had significantly lower survival, longer larval periods, lower pupal weights, and shorter pupal periods than members of the same families fed alder. Foliar nutritional quality, including nitrogen level and allelochemical composition (terpenes and phenols), was considered the key factor responsible for these differences. Growth parameters differed significantly for families within diet treatments, indicating that the genetic resources of a family did affect performance somewhat. The influence of a familys genetic resources on larval survival was most notable when larvae were under the greatest nutritional stress.