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We examined oviposition decisions by Hippodamia convergens Guerin in semi-natural arenas in the laboratory. Gravid females were presented individually with an array of four young sorghum plants, Sorghum bicolor, bearing (1) no additional stimu- lus, (2) an established colony of greenbug, Schizaphis graminum Rondani, (3) residues of conspecific larvae, and (4) greenbugs plus residues of conspecific larvae. Females laid no egg masses on type 3 plants, significantly fewer than expected by chance on type 4 plants, and significantly more on type 1 plants, with type 2 plants receiving expected numbers. Females laid 50% of egg masses on elements of the arena other than the plants, especially the cage screen, suggesting that females sought to distance their eggs farther from larval residues than the spacing of plants in the arena permitted (15 cm). When the experiment was repeated with plants exposed to larvae of Coleomegilla maculata DeGeer, the repellency was weaker. Once again, clean plants were the most preferred and aphids did not increase the acceptability of plants with larval residues. Nevertheless, only 18% of egg masses occurred off the plants and larval residues did not reduce the acceptability of aphid-bearing plants as did conspecific larval residues. Simultaneous choice tests conducted with individual third instars of both species revealed that C. maculata larvae consumed H. convergens eggs as readily as conspecific eggs, but H. convergens larvae preferred conspecific eggs to those of C. maculata. We conclude that H. con- vergens oviposition decisions are shaped by the risks of both egg cannibalism and predation.

Biotype 2 of the Russian wheat aphid, Diuraphis noxia (Mordvilko), is virulent to both sources of resistance presently available in commercial wheat, Triticum aestivum L. The performance of biotype 2 was compared with that of biotype 1 on eight wheat cultivars at two constant temperatures, and the plants were evaluated for overall damage and leaf rolling. Colonies of biotype 2 grew an average of 2.3 and 24.9 times faster in the first and second generation, respectively, than did their biotype 1 counterparts at 20°C, reaching 80 to 125 aphids per plant after 20 d, compared with 10 to 31. The no. of aphids per plant at 10 and 20 d after infestation displayed a significant biotype-temperature interaction. There was also a biotype-temperature interaction for plant damage at 10 d, and for damage and leaf rolling at 30 d. After 20 d at 24°C, damage ratings ranged from 7.3 to 8.6 on a scale of 1.0 to 9.0, and leaf rolling ranged from 2.4 to 2.9 on a scale of 1.0 to 3.0 for biotype 2, whereas values for biotype 1 ranged from 2.8 to 5.1 and 1.4 to 2.2, respectively. There were no differences among cultivars in plant damage or leaf rolling induced by biotype 2, and ratings of both were higher than for biotype 1 in all cultivar-temperature combinations. Biotype 2 D. noxia has overcome both Dn4- and Dny-based sources of resistance, was more virulent than biotype 1 to all the cultivars tested, and induced plant injury more rapidly than biotype 1, especially at higher temperatures.

Late instar larvae of the army cutworm, Euxoa auxiliaris (Grote), infested replicated test plots of 43 wheat varieties in Hays, Kansas in early April, 2004. Five varieties, Trego, 2147, Betty, Thunderbolt, and Jagger, were selected for sampling cutworm defoliation and larval densities. Damage was lowest in Trego (12–41 damaged tillers/m of row), and highest in Betty (128–285 damaged tillers/m). Plots of Betty averaged 105 cutworms/m2, significantly more than plots of other varieties where densities ranged from 13 to 42 cutworms/m2. Plots of Thunderbolt sustained significantly more damage than plots of 2137, Trego or Jagger, but did not have significantly more larvae. The small size of the test plots appeared to facilitate aggregation of cutworms in plots of the preferred variety Betty. Grain yields of all varieties in 2004 were average for the region and the final grain yield of Betty plots averaged 20% less than that of Thunderbolt and Trego plots. This compares to an average of 10% lower yield ...

In spring 2003, several outbreaks of the Russian wheat aphid, Diuraphis noxia (Mordvilko), were reported in fields of supposedly resistant wheat cultivars (‘Stanton’, ‘Halt’, and ‘Prairie Red’) in eastern Colorado. We conducted two laboratory experiments to compare the biological performance of this new biotype 2 (B2) to that of two D. noxia collections of biotype 1 (B1) from western Kansas by using three wheat cultivars as host plants: ‘Trego’, a susceptible cultivar, and Stanton and Halt, two cultivars with different genetic sources of resistance. Survival of solitary nymphs from first instar to adult for the two clones of B1 on Trego was 96 and 90%, respectively, compared with 67 and 43% on Stanton, and 65 and 57% on Halt. In contrast, B2 had 60% survival on Trego, 43% survival on Halt, and 85% survival on Stanton. One clone of B1 required longer to mature on Halt compared with Trego or Stanton, but no other differences in developmental time among cultivars were significant. The standardized fecundity of solitary foundresses of the B1 clones was 19.6 and 20.1 nymphs on Trego, compared with 4.6 and 0.9 on Stanton, and 2.8 and 1.1 on Halt, respectively, over the same period. In contrast, fecundity of B2 was 21.1, 20.8, and 19.7 on Trego, Stanton, and Halt, respectively. When larger colonies developed on individual plants over longer periods, Trego supported the largest number of B1 aphids by experiment’s end, whereas Stanton and Halt yielded the largest numbers of B2. The order of overall plant damage was Trego > Stanton > Halt when infested with B1, with no significant differences for B2. Trego had more pronounced leaf rolling than other cultivars, independent of biotype. Collectively, the results suggest that D. noxia B2 from Colorado has evolved cross-virulence to both Dn4- and Dny-based resistance sources.

A 2 yr (1999–2000) study using water-pan traps in the field indicated four generations, including the spring generation, of cabbage maggot adults, Delia radicum (L.), in upstate New York. On average over the 2 yrs, an accumulation of 160.7 ± 8.1 degree-days and 120 ± 3 Julian-days was required for the first adult emergence of flies from overwintered puparia (spring generation). The emergence of 10% of the population required a mean accumulation of 176.6 ± 3.8 degree days and 122.0 + 1.0 Julian days, 25% emergence required 204.2 ± 2.3 degree days and 125.0 ± 1.0 Julian days, 50% emergence required 251.3 ± 3.5 degree-days and 129.3 ± 1.5 Julian days, 75% emergence required 297.6 ± 30.4 degree-days and 132.0 ± 0.0 Julian days, and 95% emergence required 390.9 ± 10.1 degree days and 141.0 ± 3.0 Julian days. From the emergence of the first adult flies, the population required a mean accumulation of 449.2 ± 1.4 degree days to complete the spring emergence. For complete emergence of flies, the F1 generation required a mean accumulation of 508.4 ± 32.9 degree days, the F2 generation required 465.3 ± 21.5 degree days and the F3 generation required 399.1 ± 3.1 degree days. With the help of a degree-days model, it is possible to predict fly emergence in the spring and succeeding generations. This model can help growers minimize insecticide use through better timing of treatments or adjustment of planting dates. In addition, this model will be useful in developing sampling plans and control strategies for immature stages of cabbage maggot.

The cabbage maggot, Delia radicum (L.), is an important chronic pest of cabbage in the northern U.S. The maggots of this species cause damage to young plants by feeding on roots and stems, resulting in plant stand and yield losses or rendering the crop unmarketable. In New York, the nation's largest producer of cabbage, the most common control practice is to apply a drench or banded spray of chlorpyrifos at transplanting. As an alternative to this practice, we investigated the duration of insecticidal activity of chlorpyrifos film-coated seeds on cabbage transplants. Seeds of the cabbage var. ‘Fresco F-1’ were film-coated with chlorpyrifos at the rates of 0, 9.6, 19.2 or 28.8 g [Al]/kg seed and then examined for phytotoxic effects on germination in the laboratory as well as effectiveness against immature stages of D. radicum under greenhouse and field conditions. Chlorpyrifos film-coated seed treatments did not adversely affect germination in the laboratory tests when plants were grown with peat soil in transplant cell trays and provided significant plant protection against immature stages of cabbage maggot through several weeks after transplanting seedlings with associated soil under greenhouse and field conditions. These results agree with previous European studies showing the potential of seed treatments to reduce damage by D. radicum while at the same time dramatically reducing the amount of insecticide compared with a banded spray or drench application.

One-d-old Heliothis virescens (F.) larvae were placed on Bacillus thuringiensis var. kurstaki Berliner-treated cotton leaves and terminals in the laboratory. Larval movement, food consumption and mortality were examined at 3, 6, 12, 24 and 48 h. Untreated leaves had a greater percentage of larvae on their under side than on their upper side; this location was not influenced by treatment with B. thuringiensis. When B. thuringiensis was applied to cotton terminals, first instars moved from B. thuringiensis-treated meristems; this movement increased with an increase in rate. Bacillus thuringiensis treatment also resulted in increased movement of larvae from the leaves and terminals onto the inner cup surface, although this movement was significantly greater than the untreated control only during the first 12 h after treatment. The leaf area consumed decreased with an increase in B. thuringiensis rate, but was not significantly correlated with larval mortality.

A commercial formulation of Bacillus thuringiensis variety kurstaki Berliner (Javelin) was evaluated 2 d after application at 0.02.5,0.1, and 0..5 kg/ha to cotton leaves and terminals for its effect on location, mortality, and leaf area consumption of exposed bollworm, Helicocerpa zea (Boddie), larvae. On leaves held in paper cups the percentage of larvae in the control was typically higher on the lower than upper surface, and results were similar at all B. thuringiensis rates and times. Increasing the B. thuringiensis rate also significantly decreased leaf area consumption, which was correlated inversely with larval mortality. Application of B. thuringiensis to cotton terminals resulted in a decrease in the percentage of live larvae located on meristematic tissue and squares at all sampling times (3, 6, 12, 24, and 48 h) and an increase in the percentage on the holding cup surface and the terminal leaves. except at 48 h. The percentage of live larvae on the meristematic tissues and squares at the 2 highest B. thuringiensis rates after 6 h had been reduced 36 and 50% and 73 and 64%, respectively. from the control. These results show that within hours of B. thuringiensis application to cotton terminals there is a significant shift in the location of H. zea larvae away from meristematic tissue and squares to expended leaves or off the terminal, or both. This suggests that adequate B. thuringiensis consumption causes larval movement to locations where larvae are less damaging.

We conducted a 2-yr study to determine the effects of crop density and weeds on levels of damage caused by stalk-boring insects in rain-fed sunflowers in west-central Kansas. Weed-free sunflower had higher seed weight and oil content in 2007, but not in 2006, but weeds did not affect infestation by stalk-boring insects in either year. High-density sunflower had lower estimated seed yield per unit area than low-density sunflower in both years, but percentage oil was slightly greater in the high-density treatment in 2006. Sunflowers were more heavily infested by larvae of Ataxia hubbardi Fisher, Cylindrocopturus adspersus (Leconte), and Pelochrista womanana (Kearfott) in 2006 than in 2007, ostensibly as a result of being planted earlier. Larvae of Dectes texanus LeConte appeared unaffected by planting date and were present in70% of plants in both years. Conditions during the period of crop maturity were much drier in 2006 than in 2007 and were associated with higher seed oil content and earlier and faster progression of stalk girdling by D. texanus larvae in both low- and high-density plots. There was also a strong effect of plant density on girdling behavior that seemed to be mediated by effects on soil moisture. Stalk girdling began earlier in high-density plots and a larger proportion of plants were girdled compared with low-density plots on all sampling dates in both years. Certain cultural tactics, in particular reduced plant spacing, have potential to delay the onset of girdling behavior by D. texanus larvae and thus mitigate losses that otherwise result from the lodging of girdled plants.

Changes in fitness parameters as a function of colony size (one versus 10 aphids) were measured in two biotypes (RWA1 and RWA2) of the Russian wheat aphid, Diuraphis noxia (Mordvilko) (Homoptera: Aphididae), feeding on three cultivars of wheat, Triticum aestivum L., at two temperatures. 'Trego' is a cultivar with no specific resistance to D. noxia, whereas, 'Stanton' and 'Halt' express Dny and Dn4 resistance sources, respectively. Feeding in a group accelerated the development of RWA1 on Trego and Stanton at 20 degrees C, but not at 24 degrees C, whereas grouped RWA2 developed faster than solitary RWA2 on all three cultivars at 24 degrees C, but not at 20 degrees C. Survival (first instar-adult) of RWA2 also was improved by grouping on Stanton and Halt at 24 degrees C, but solitary RWA2 survived better at 20 degrees C on all three cultivars. The reproductive rate of RWA1 was improved by grouping on Trego and Stanton at both temperatures, but only on Halt at 24 degrees C. Lifetime fecundity of RWA1 also was increased by grouping in all cases except for Trego at 20 degrees C. Grouped development increased the reproductive rate of RWA2 on all three cultivars at 24 degrees C, but had no effect at 20 degrees C. Grouped RWA2 developed and reproduced faster than grouped RWA1 on all three cultivars at 24 degrees C. Thus, the fitness of D. noxia was positively correlated with group size during colony establishment, but the effects were sensitive to temperature, being more pronounced at 20 degrees C for RWA1 and at 24 degrees C for RWA2.

The cabbage maggot, Delia radicum (L.) is an important insect pest of cruciferous crops in upstate New York. This species causes considerable damage to seedlings and young plants by feeding on roots and stems, resulting in plant stand loss and yield loss. Five crucifer accessions (Brassica oleracea variety italica L., ‘Green Comet’; B. oleracea L., ‘Rapid Cycling’ [Crucifer Genetics Cooperative 3–1]; B. oleracea variety botrytis L., a standard cauliflower cultivar ‘Amazing’; B. carinata L.; and Sinapis alba L., ‘Cornell Alt 543’) were evaluated to identify sources and mechanisms of resistance for D. radicum. Of the accessions tested, S. alba Cornell Alt 543 demonstrated reduced oviposition by D. radicum, reduced weights and survivorship of larvae, pupae or adults, and reduced damage to plants. Thus, S. alba Cornell Alt 543 could be a potential source for resistance to be bred into cruciferous crops for control of D. radicum.