David N. Ferro

Importance of plant size, distribution of egg masses, and weather conditions on egg parasitism of the European corn borer, Ostrinia nubilalis by Trichogramma ostriniae in sweet corn

Trichogramma ostriniae (Hym: Trichogrammatidae), an egg parasitoid of the European corn borer, Ostrinia nubilalis (Lep: Pyralidae), were released into sweet corn (Zea mays L.) fields to study the effects of weather, plant size and distribution of egg masses on egg parasitism by the wasp. Sentinel European corn borer eggs were stapled onto leaves located in the upper, middle and lower third of sweet corn plants 5 to 35 meters away from the wasp release point in either a radial or grid manner. Weather conditions and plant architecture were monitored during the experiments. Logistic regression was used to analyze the data. The results indicated that percentage of eggs parasitized was negatively related to an increase in leaf area as well as an increase in distance eggs were located from the point of release of wasps. Eggs distributed on plants at different directions from the release point received different levels of parasitism. Eggs that were stapled onto leaves in the upper third of a corn plant received much less parasitism than those on the middle and lower third of the plant. Higher mean temperature adversely affected the level of parasitism during hotter times of the season and conversely, lower temperatures (<17 °C ) reduced the egg parasitism during cooler times of the season. The longer the exposure of eggs to wasps, the higher the level of egg parasitism. However, the levels of egg parasitism for 2 days exposure were almost the same as that for 3 days exposure due to the limited longevity and egg‐laying behavior of the wasp. These results suggest that inundative releases of T. ostriniae should be made every two to three days, with multiple release points per hectare. In addition, weather conditions and plant architecture, especially temperature, plant height and leaf area must be taken into consideration to optimize levels of parasitism.

Distribution of overwintering Colorado potato beetle in and near Massachusetts potato fields.

The Colorado potato beetle (CPB), Leptinotarsa decemlineata (Say), is a major pest of potatoes and other Solanaceae in the north temperate zones. Its diapause responses are variable both within and among populations (de Wilde & Hsiao, 1981; Tauber et al., 1988; Biever & Chauvin, 1990). The majority of diapause investigations have been in the lab, or with artificiallyconfined populations under field conditions. Studies of diapause phenomena and post-diapause movement in the CPB have not investigated quantitatively the natural distribution of overwintering beetles in croplands and adjacent habitats. This investigation is important to any attempt to understand and manage the spring colonization of crops by the overwintered adults. During August and early September 1990, thousands of beetles were observed making diapause flights (sensu Voss & Ferro, 1990a) to the borders of a large (20 ha) field in Southwick, Massachusetts. In late September, approximately 1500 beetles were collected in less than four manhours by simply digging with shovels in this border zone. A more systematic effort to document the distribution of diapausing beetles was undertaken the following spring. Materials and methods

Effectiveness of Trichogramma ostriniae and T. nubilale for controlling the European corn borer Ostrinia nubilalis in sweet corn

Seven field releases of Trichogramma ostriniae and T. nubilale (Hymenoptera: Trichogrammatidae) were made separately and in combination in a sweet corn field to compare the level of parasitism in sentinel eggs of the European corn borer, Ostrinia nubilalis (Lepidoptera: Pyralidae). The results indicate that the levels of egg parasitism among different release dates differed mainly because of changes in weather and plant architecture within the season. The level of egg parasitism by releasing T. ostriniae alone was found to be 15% higher than that by releasing T. nubilale alone, and 20% higher than by releasing the combination of the two species. Further analyses using the logistic regression model for independent and correlated data indicated T. ostriniae to be more efficient at discovering host egg masses and to have higher levels of egg parasitism than T. nubilale. Mutual interference between T. ostriniae and T. nubilale was the main factor for the lower level of egg parasitism when T. ostriniae and T. nubilale were released together. The results suggest that T. ostriniae is the better candidate for augmentative releases for control of the European corn borer, and the two species should not be released into a corn field at the same time.

DISRUPTING SPRING COLONIZATION OF COLORADO POTATO BEETLE TO NONROTATED POTATO FIELDS

Overwintering Colorado potato beetles (Leptinotarsa decemlineata (Say)) were concentrated primarily within woody borders, and mortality was lower in borders than in potato fields. After overwintering, only 15–44% of live beetles were in the potato fields. In experiments with small plots, colonization of fields from woody borders was reduced ∼ 60% by a trap crop, either treated with adulticide or with beetles collected daily. Such trap crops, or simply pitfall traps to prevent colonization from woody borders, could significantly reduce early‐season adult numbers and subsequent larval populations. However, success is dependent on the local densities of overwintered beetles, and the prevalence of arrestment behavior in the case of trap crops.

Persistence and Inheritance of Costs of Resistance to Imidacloprid in Colorado Potato Beetle

Abstract Reduced fitness among resistant versus susceptible individuals slows resistance evolution and makes it easier to manage. A loss of resistance costs could indicate novel adaptations or mutations contributing to resistance. We measured costs of resistance to imidacloprid in a Massachusetts resistant population compared with a Massachusetts susceptible population in 1999 in terms of fecundity, hatching success, egg development time, and sprint speed. Resistance was additive and seemed to be polygenic with high heritability. The fecundity cost appeared overdominant in 1999, and the hatch rate cost was partly recessive in 1999, but neither was significantly different from dominant or recessive. In 2004, we repeated our measures of resistance costs in Massachusetts in terms of fecundity and hatching success, and we added a new resistant population from Maine. In 2005, we compared development time of Maine resistant and the laboratory susceptible colony eggs. Significant fecundity costs of resistance were found in both population in both 1999 and 2004, and significant egg developmental time costs were found in 1999 and 2005. However, the hatching success costs of resistance were significant in 1999 and not apparent in 2004, suggesting some modification or replacement of the resistance genes in the intervening time.

Role of visual and olfactory stimuli in host finding of adult cabbage root flies, Delia radicum

Visual host finding and form recognition by the cabbage root fly, Delia radicum, were studied using four shapes of yellow sticky traps as plant models. Cross, disc, and Y traps caught similar numbers of flies. Cross traps caught more females than ‘vertical’ or ‘horizontal’ rectangular traps. Black borders did not increase rectangle trap catches. Discs (8 cm diam.) at ground level caught more females than discs at 40 cm above ground. Larger discs (11.2 and 13.8 cm diam.) caught more females per trap than 8 cm diam. discs, but not as many per unit area.

Reproductive status and flight activity of the overwintered Colorado potato beetle

Mating behavior of post‐diapause Colorado potato beetles, Leptinotarsa decemlineata (Say), was observed within an overwintering site, a rotated potato field, newly colonized potato plants, and under laboratory conditions. The influence of spring mating on beetle flight in the presence and in the absence of host plants was investigated using a computer‐linked flight mill system. Diapause was terminated simultaneously in male and female beetles, and the first matings were observed as early as within the first 24 h after the beetles emerged from the soil (60–90 DD accumulated). The beetles mated within the overwintering site, the potato field, and the fields rotated out of potatoes. Mating status did not affect flight behavior of overwintered beetles; however, unfed beetles displayed higher flight activity than fed beetles. Most flight activity took place soon after flight muscle regeneration, and then declined sharply by the 5th day after flight initiation. Mating in or near overwintering sites soon after diapause termination might be an important factor in providing gene flow between insecticide‐resistant and insecticide‐susceptible Colorado potato beetle populations, and should be considered in designing resistance management plans.

Modifications in dispersal and oviposition of Bt‐resistant and Bt‐susceptible Colorado potato beetles as a result of exposure to Bacillus thuringiensis subsp. tenebrionis Cry3A toxin

Laboratory strains of Colorado potato beetle, Leptinotarsa decemlineata (Say), physiologically resistant and susceptible to Bacillus thuringiensis (Berliner) subsp. tenebrionis Cry3A toxin were reared to adults on caged potato plants. Influence of three different diets (transgenic potatoes, regular potatoes, and regular potatoes followed by the transgenic potatoes) on beetle mortality, fecundity, and flight behavior were tested under laboratory conditions. A computer‐linked flight mill system was used to quantify beetle flight, and dissections were performed to determine the level of flight muscle development. Susceptible beetles continuously fed on transgenic foliage suffered heavy mortality, did not develop flight muscles, and did not produce any eggs. Resistant beetles continuously fed on transgenic foliage were capable of flight and reproduction; however, it took them longer to initiate flight behavior, and their fecundity was lower than fecundity of other treatments. In both strains, detrimental effects became significantly less severe when the beetles were allowed to feed on regular foliage prior to toxin ingestion. In the resistant strain, ingestion of Cry3A toxin significantly increased flight activity, indicating that physiological resistance was probably reinforced by the behavioral escape from toxic environments. No such response was observed for susceptible beetles. When fed on regular foliage, resistant Colorado potato beetles engaged in significantly fewer flights than susceptible beetles. Behavioral differences between resistant and susceptible beetles observed in the present study are likely to affect gene flow between transgenic crops and adjacent refugia, and should be taken in consideration when designing resistance management plans for transgenic potato crops.

Population dynamics of the Colorado potato beetle (coleoptera:chrysomelidae) in western Massachusetts

Population trends for first-and second-generation Colorado potato beetle (CPB),Leptimtarsa decemlineata (Say), on potato in western Massachusetts were examined using density estimates obtained from direct counts of eggs, early and late instars, and adults. There was a range of phenologies and relative sizes of first-and second-generation populations. The size of the first generation was largely determined by the density of colonizing adults; however, even very low numbers of colonizing adults were sufficient to initiate damaging populations. The number of adults produced one year was not a good predictor of the number of colonizing adults the following year. This study indicated that dispersal was an important factor driving CPB population dynamics. Because dispersal and overwintering mortality greatly reduce the number of adults surviving from one year to the next within the same field, we suggest that reduction of end-of-season adult populations is not efficacious, and that control efforts should focus on reducing the number of colonizing adults by rotating fields, delaying planting dates or using a trap crop.CompendioSe examinaron las tendencias para la primera y segunda generación del escarabajo de la papa de Colorado (CPB),Leptimtarsa decemlineata (Say), en el oeste de Massachusetts, utilizando estimados de densidad obtenidos de la cuenta directa de huevos, estadios tempranos y tardíos, y adultos. Se observó un rango fenológico y tamaños relativos de las poblaciones de primera y segunda generación. El tamaño de la primera generación fue mayormente determinado por la densidad de adultos colonizadores; sin embargo, aun un número muy reducido de adultos colonizadores fueron suficientes para iniciar poblaciones dañinas. El número de adultos producidos un año no fue un buen argumento para pronosticar el número de adultos colonizadores del año siguiente. Este estudio indicó que la dispersión fue un factor importante DRIVING la dinámica de la población del CPB. Debido a que la dispersión y la mortalidad durante el invierno reducen considerablemente el número de adultos sobrevivientes de un año al otro dentro del mismo campo, se sugiere que la reducción de las poblaciones de adultos al final de la temporada no es eficaz y que las labores de control deben concentrarse en reducir el número de adultos colonizadores mediante la rotacion de campos, atrasar la fecha de siembra o utilizar cultivos trampa.

Habitat enhancement and conservation of natural enemies of insects

Publisher Summary The chapter describes the effects of diversifying agricultural landscapes on insect pests and their natural enemies, in and unto themselves, as highly variable. A much better understanding of the ecology of parasitoids and predators outside their cultivated habitat needs to be achieved, and the resources that are necessary for their survivorship and reproduction need to be identified. The extent to which populations within the crop contribute to the metapopulation in subsequent years also needs to be determined. A specific modification of the landscape may prove beneficial with respect to one specific insect pest, but any potential actions need to be evaluated within the context of a broader integrated management program of the agricultural crop. The reason for caution is that potential benefits may be less than unforeseen costs. Thus, an action taken to increase the efficacy of natural enemies may incur losses through increased levels of disease. Thus, an action taken to increase the efficacy of natural enemies may incur losses through increased levels of disease. Intraguild predation may also increase if several species of natural enemies are favored as a result of habitat management. This may result in a lower impact on the target pest, despite a rise in the densities of natural enemies.