Joseph P. McCaffrey

Allelochemicals produced during glucosinolate degradation in soil.

A variety of plant pests are suppressed by the incorporation of cruciferous plant material into soil. Although this effect is attributed to decomposition of glucosinolates into toxic products, little is known concerning glucosinolate degradation in the soil environment. Arenas (30 × 18 × 8 cm) that contained soil amended with 30 g defatted winter rapeseed meal (Brassica napus L.)/kg soil on one half and unamended soil on the other were constructed. Isothiocyanate concentrations in the soil were measured using infrared analysis of CC14 extracts, and ionic thiocyanate (SCN−) using ion chromatography on aqueous extracts. Quantities were monitored during a 100-hr time period in conjunction with a wireworm bioassay. Isothiocyanate production reached a maximum of 301 nmol/g soil at 2 hr, but decreased by 90% within 24 hr. Production of SCN− reached a maximum of 180 nmol/g soil at 8 hr but persisted longer than isothiocyanate. Separate late instar wire-worms (Limonius infuscatus Mots.) were repelled by the presence of rapeseed meal in less than 24 hr even though the meal was shown in separate experiments not to be toxic. We propose that rapidly produced isothiocyanates are responsible for this repellency, but other products such as SCN− may play a role.

Effect of late season insect infestation on yield, yield components and oil quality of Brassica napus , B. rapa , B. juncea and Sinapis alba in the Pacific Northwest region of the United States

The effect of late season insect infestation on seed yield, yield components, oil content and oil quality of two canola species ( Brassica napus L. and B. rapa L.) and two mustard species ( B. juncea L. and Sinapis alba L.) was examined over 2 years. In each year, ten genotypes from each species were evaluated with late season insects controlled with either methyl parathion or endosulfan insecticides, and without insecticides. Major late season insect damage in 1992 was caused by cabbage seedpod weevil ( Ceutorhynchus assimilis Paykull), while diamondback moth ( Plutella xylostella L.) and aphids (primarily cabbage aphids, Brevicoryne brassicae L.) were major insect pests in 1993. Insecticide application was very effective in controlling diamondback moth larvae and adult cabbage seedpod weevils, but only partially effective in controlling aphids. Higher numbers of diamondback moth larvae were observed on mustard species compared to canola species. S. alba was completely resistant to cabbage seedpod weevil and there was no damage due to this pest observed. Aphid colonization was observed on plants from all species, but infestation on S. alba and B. rapa occurred too late to have a major effect on seed yield. Seed oil content of canola species was significantly reduced by insect damage although oil quality (indicated by fatty acid profile) was not affected by insect attack. Uncontrolled insect infestation reduced seed yield of canola species by 37 and 32% in B. napus and B. rapa , respectively. Least yield reduction occurred in S. alba , where average yield reduction from plants in untreated control plots was S. alba , therefore, has good potential as an alternative crop suitable for northern Idaho because it can be grown with reduced late season insecticide application.

Toxicity of allyl isothiocyanate-amended soil toLimonius californicus (Mann.) (Coleoptera: Elateridae) wireworms

Acute toxicity of soil amended with allyl isothiocyanate (AITC) to three size classes ofLimonius californicus (Mann.) wireworms was determined in the laboratory. Wireworms were exposed to AITC at initial concentrations of 120–300 nmol/g soil for one day. During this time, extractable AITC concentrations decreased by 66 to 93 %. Probit analysis estimated LC50 values of 238 and 226 nmol/g soil at one day posttreatment for medium and large wireworms, respectively. For small wireworms, LC50 values decreased from 211 to 157 nmol/g soil during 1–137 days posttreatment. Sublethal concentrations of AITC significantly reduced feeding activity of treated wireworms at three posttreatment times and over the entire 137 days. Wireworm weight was not significantly affected by AITC. The potential exists to use glucosinolate-containing plant tissue as an isothiocyanate (ITC) source to reduce crop damage caused byL. californicus wireworms.

Assessment of Sinapis alba, Brassica napus and S. alba × B. napus hybrids for resistance to cabbage seedpod weevil, Ceutorhynchus assimilis (Coleoptera: Curculionidae).

Canola (Brassica napus L.), yellow mustard (Sinapis alba L.) and intergeneric crosses of S. alba × B. napus were assessed for resistance (antixenosis) to the cabbage seedpod weevil (Ceutorhynchus assimilis Paykull). Pod trichomes did not appear to be a major factor in the resistance of S. alba to weevils. The number of feeding punctures and eggs per pod in S. alba was not significantly different in pods with trichomes than in those where the trichomes had been removed. Choice and no-choice laboratory tests examining feeding punctures and eggs laid per pod suggested that resistance in S. alba is not conferred in the intergeneric cross, S. alba × B. napus. Similar data on feeding and weevil oviposition were found in field test plots. However, despite many eggs being laid in S. alba × B. napus hybrid plants, fewer cabbage seedpod weevil larvae developed to exit the intergeneric hybrid pods. Glucosinolate analyses of leaves, pods and seeds showed that S. alba plants have a high concentration of p-hydroxybenzyl glucosinolate in all three plant parts, but B. napus has no p-hydroxybenzyl. Interestingly the intergeneric hybrid examined in this study had 62% and 60% of p-hydroxybenzyl concentration in the leaves and seeds, respectively, than was found in the S. alba parent. However, pod tissues contained very little (3 %) compared with the S. alba parent. It is possible, therefore, that the adult cabbage seedpod weevil feeds on the pods of the intergeneric hybrid and lays eggs in the pod, because of the low concentration ofp-hydroxybenzyl glucosinolate, but the larvae then fail to develop as they feed on the seeds containing high concentrations of p-hydroxybenzyl glucosinolate. It should be noted also that this hybrid produced pods that were more similar in physical shape to canola pods and that this may also be a factor determining cabbage seedpod weevil feeding and subsequent egg laying. In addition, both B. napus and the intergeneric hybrid produced 3-butenyl and 4-pentenyl glucosinolates in their pods, and degradation products (3-butenyl, and 4-pentenyl isothiocyanates) from these glucosinolate types, are known to be stimulatory kairomones that attract cabbage seedpod weevil. Further studies are being conducted to examine these factors in more detail.

Yield Reduction in Brassica napus, B. rapa, B. juncea, and Sinapis alba Caused by Flea Beetle (Phyllotreta cruciferae (Goeze) (Coleoptera: Chrysomelidae)) Infestation in Northern Idaho

Abstract Phyllotreta cruciferae is an important insect pest of spring-planted Brassica crops, especially during the seedling stage. To determine the effect of early season P. cruciferae infestation on seed yield, 10 genotypes from each of two canola species (Brassica napus L. and Brassica rapa L.) and two mustard species (Brassica juncea L. and Sinapis alba L.) were grown in 2 yr under three different P. cruciferae treatments: (1) no insecticide control; (2) foliar applications of endosulfan; and (3) carbofuran with seed at planting plus foliar application of carbaryl. Averaged over 10 genotypes, B. rapa showed most visible P. cruciferae injury and showed greatest yield reduction without insecticide application. Mustard species (S. alba and B. juncea) showed least visible injury and higher yield without insecticide compared with canola species (B. napus and B. rapa). Indeed, average seed yield of S. alba without insecticide was higher than either B. napus or B. rapa with most effective P. cruciferae control. Significant variation occurred within each species. A number of lines from B. napus, B. juncea, and S. alba showed less feeding injury and yield reduction as a result of P. cruciferae infestation compared with other lines from the same species examined, thus having potential genetic background for developing resistant cultivars.

Phenological Synchrony of Eustenopus villosus (Coleoptera: Curculionidae) with Centaurea solstitialis in Idaho

Abstract The phenological synchrony of Eustenopus villosus (Boheman) with its host, yellow starthistle, Centaurea solstitialis L. (Asteraceae: Cardueae), was studied in Idaho in 1995 and 1996. Field plots were observed for adult weevil activity periodically throughout the growing season, and yellow starthistle capitula were examined for adult feeding damage, oviposition damage, and larval development. At the study site, weevil phenology was well synchronized with C. solstitialis. Immature capitula, fed upon by adults, were abundant when E. villosus began to emerge in late May. During both years, the number of weevils and capitula increased throughout June. Adult females fed on capitula for about 2 wk. Weevil ovary dissections revealed that ovaries were mature after a 2-wk period of feeding. The development of mature capitula during late July corresponded to the initiation of oviposition. Eustenopus villosus, unique among the phytophages introduced for C. solstitialis biological control, attacks four plant stages resulting in observable impact to buds. Damaged buds either died or became distorted. Weevil feeding damage on young and mature capitula may make this insect a highly effective control agent.

Phenological Synchrony ofEustenopus villosus(Coleoptera: Curculionidae) withCentaurea solstitialisin Idaho

Abstract The phenological synchrony of Eustenopus villosus (Boheman) with its host, yellow starthistle, Centaurea solstitialis L. (Asteraceae: Cardueae), was studied in Idaho in 1995 and 1996. Field plots were observed for adult weevil activity periodically throughout the growing season, and yellow starthistle capitula were examined for adult feeding damage, oviposition damage, and larval development. At the study site, weevil phenology was well synchronized with C. solstitialis. Immature capitula, fed upon by adults, were abundant when E. villosus began to emerge in late May. During both years, the number of weevils and capitula increased throughout June. Adult females fed on capitula for about 2 wk. Weevil ovary dissections revealed that ovaries were mature after a 2-wk period of feeding. The development of mature capitula during late July corresponded to the initiation of oviposition. Eustenopus villosus, unique among the phytophages introduced for C. solstitialis biological control, attacks four plant stages resulting in observable impact to buds. Damaged buds either died or became distorted. Weevil feeding damage on young and mature capitula may make this insect a highly effective control agent.

Resistance of canola-quality cultivars of yellow mustard, Sinapis alba L., to the cabbage seedpod weevil, Ceutorhynchus obstrictus (Marsham)

Oilseed Bassica is susceptible to attack by the cabbage seedpod weevil while commercial yellow mustard, Sinapis alba L., is resistant. The objective of this study was to determine if canola-quality S. alba would maintain its resistance traits. In laboratory choice and nochoice tests we found the number of eggs laid by the weevil to be low or non-existent in all S. alba genotypes. Key words: Ceutorhynchus obstrictus, Ceutorhynchus assimilis, Sinapis alba, plant resistance

Insecticidal activity of Brassica juncea seed meal to the fungus gnat Bradysia impatiens Johannsen (Diptera:Sciaridae)

Fungus gnats (Bradysia impatiens) can be a serious pest especially to plants grown in confined areas, and although various methods of control are available, safer and more effective control measures are desirable. Mustard seed meal, a by‐product remaining after oil removal for use as a biodiesel feedstock, contains compounds called glucosinolates that hydrolyse to insecticidal 2‐propenyl isothiocyanate. Our objective was to produce a dose‐response curve for making recommendations of Brassica juncea seed meal applications that will result in fungus gnat larvae control. Twenty colony‐raised fungus gnat larvae were added to 20 g (226 per cm3) of potting media, and adult emergence monitored during 2 weeks using yellow sticky cards. Treatments included without meal, detoxified meal and 19 doses ranging from 0.05 to 3.0 g seed meal. A logistic model was used to predict an LC50 of 0.18 and an LC90 of 0.38 g seed meal for the 20‐g pot. The amounts of seed meal required to produce the observed LC50 and LC90 were predicted to produce 0.08 and 0.17 μmol 2‐propenyl isothiocyanate per cm3 potting medium, respectively. B. juncea seed meal has potential utility for the control of B. impatiens, thus warranting additional studies to determine the seed meals chronic impact on fungus gnats, phytotoxicity and plant fertility benefits.

Cabbage seedpod weevil resistance in canola (Brassica Napus L.) yellow mustard (Sinapis alba L.) and canola × yellow mustard hybrids

Canola, yellow mustard and yellow mustard × canola hybrids were screened for resistance to Ceutorhynchus obstrictus (Marsham) in a series of greenhouse and laboratory choice tests. Tests were conducted using small and large cages designed to hold Brassica pods or whole plants, respectively, with ovipositing female C. obstrictus. Pods were examined for feeding punctures, eggs laid and exit holes that resulted from emerging larvae. All yellow mustard cultivars examined were highly resistant to C. obstrictus feeding and egg laying. In addition, hybrid lines were found with significantly reduced feeding punctures, oviposition, and exit holes compared with canola. A negative relationship was observed between total glucosinolate content of seed and C. obstrictus resistance; however, in both detached pod and whole plant choice tests, hybrids were identified with high seed glucosinolate content that were more susceptible than the most susceptible canola. The relatively poor association between total seed meal glu...