Donna Ellis

IS PURPLE LOOSESTRIFE (LYTHRUM SALICARIA) AN INVASIVE THREAT TO FRESHWATER WETLANDS? CONFLICTING EVIDENCE FROM SEVERAL ECOLOGICAL METRICS

Conflicting interpretations of the negative impacts of invasive species can result if inconsistent measures are used among studies or sites in defining the dominance of these species relative to the communities they invade. Such conflicts surround the case of Lythrum salicaria (purple loosestrife), a widespread exotic wetland perennial. We describe here a 1999 study in which we quantified stand characteristics of L. salicaria and associated vegetation in arrays of 30 1-m2 plots in each of five wet meadows in Connecticut, USA. We explored linear and non-linear relationships of above-ground plant biomass, stem density, and indices of species richness, diversity, and composition to gradients of L. salicaria dominance, including stem density, percent cover, and biomass. Species richness, other diversity metrics, and stem density of other species were not significantly correlated with the density or percent cover of L. salicaria stems. The relative importance values (number of quadrats in which they were found) of co-occurring species in low-density L. salicaria quadrats were significantly correlated with their relative importance in high-density L. salicaria quadrats, indicating that only modest shifts in abundance occurred as L. salicaria increased in density. No individual species were consistently associated with or repelled by the presence of L. salicaria across sites. In contrast to density and diversity features, however, the total biomass of species other than L. salicaria was significantly, negatively correlated with the total biomass of L. salicaria at each site surveyed. Lythrum salicaria in pure, dense stands maintained a greater above-ground standing biomass on invaded sites than uninvaded vegetation of similar physiognomy. This study demonstrates that hypotheses about L. salicaria effects can vary depending upon the ecological metric that is examined. Where one-time, correlative studies are the most feasible option, data taken on a range of metrics—especially biomass—should be taken to inform us about mechanisms by which L. salicaria invades and predominates in wetlands.

Invasive Ornamental Plants: Problems, Challenges, and Molecular Tools to Neutralize Their Invasiveness

The spread of invasive plants is one of the most challenging ecological problems in the 21st Century, causing a

EVALUATION OF SERANGIUM PARCESETOSUM (COLEOPTERA: COCCINELLIDAE) FOR BIOLOGICAL CONTROL OF SILVERLEAF WHITEFLY, BEMISIA ARGENTIFOLII (HOMOPTERA: ALEYRODIDAE), ON POINSETTIA

35 billion loss per year to the economy in the United States alone. More than 50% of all invasive plants and 85% of invasive woody species were introduced originally for ornamental and landscape use. Because many nonnative plants are commercially important and widely utilized for various purposes, completely banning their use and prohibiting their imports are unpractical solutions for control. On the other hand, the methods currently used to control the spread of nonnative plants are ineffective, expensive, or environmentally problematic. Recent advances in plant biotechnology may enable us to create sterile cultivars of these nonnative ornamental crops of commercial value. The use of sterile cultivars should reduce or eliminate the undesirable spread of some nonnative invasive plants into natural areas.

Purslane as a living mulch in broccoli production

Control of silverleaf whitefly (Bemisia argentifolii Bellows & Perring) on greenhouse poinsettia with biological agents has been unreliable. Serangium parcesetosum Sicard, a coccinellid predator, appears to have great potential for silverleaf whitefly control. In our study, dynamic changes in B. argentifolii populations on caged poinsettia in response to S. parcesetosum were monitored. Silverleaf whiteflies were introduced to caged poinsettias at 1 or 10 adults per plant and 6 weeks later S. parcesetosum were introduced at 0, 2 or 4 adults per plant. Within 2 weeks of Serangium release whitefly mortality increased dramatically, and for the ensuing 10 weeks whitefly levels remained at or near those observed at time of predator release. Beetle larvae were observed 2 to 10 weeks after Serangium release when prey was initially high but not when prey was initially low. Thus, whitefly control was primarily due to prolonged survival and continuous feeding of individual beetles. Our data suggest that Serangium may work well in a multiple species biological control program for whiteflies on poinsettia. However, further study is needed on multiple species interactions within the host (pest/plant) species, and on release management strategies.

Problems and Challenges of Invasive Ornamental Plants and Molecular Tools to Control Their Spread

Many of the characteristics of common purslane that describe this species as a “weed” are also desirable traits for a living mulch. Common purslane was investigated as a living mulch in spring broccoli production in Connecticut and was compared with mechanical and chemical weed control, as well as black plastic mulch. Common purslane seed was broadcast prior to transplanting broccoli in late May 1993 and in early June 1994. Broccoli yields with the purslane living mulch were comparable to yields with conventional methods of weed management and with no reduction in crop quality. Common purslane living mulch was able to effectively compete with weeds in broccoli when between-row areas were kept relatively weed-free by hoeing or hand pulling during the first 2 weeks after broccoli transplanting. High levels of weed control and ground cover occurred when purslane became established between crop rows. Broccoli plants were tolerant of purslane living mulch and weeds up to a critical threshold level without a significant reduction in yield. Purslane living mulch established through periodic mechanical weed management was determined to be the most economical treatment in the study. While including purslane living mulch in a spring broccoli crop production system may be a novel approach to controlling weeds, the strategies involved in this system still rely on basic weed management principles.

Fall applications of MCPA to improve tiller synchrony and reduce lodging in winter wheat

Abstract Invasive plants, one of the most devastating ecological problems in the 21st century, cause an estimated

EXOTIC LADY BEETLE SURVEY IN NORTHEASTERN UNITED STATES : HIPPODAMIA VARIEGATA AND PROPYLEA QUATUORDECIMPUNCTATA (COLEOPTERA : COCCINELLIDAE)

35 billion loss per year to the economy in the United States alone. More than 50% of all invasive plant species and 85% of invasive woody plant species were introduced originally for ornamental and landscape use. Because many non-native ornamentals are commercially important and widely utilized for various purposes, completely banning their use and prohibiting their import are unpractical solutions. On the other hand, currently used methods to control the spread of non-native plants are ineffective, expensive, or environmentally problematic. Recent advances in plant molecular biology and plant genetic transformation may enable us to create sterile cultivars of these non-native ornamental crops of high commercial value. The use of sterile cultivars should reduce or eliminate the undesirable spread of some non-native invasive plants into natural areas.

In vitro regeneration and Agrobacterium-mediated genetic transformation of Euonymus alatus

Poor developmental spike synchrony in wheat (Triticum aestivum L.) can reduce the effectiveness of chemical treatments keyed on reproductive events. The broadleaf herbicide (2-methyl-4-chlorophenoxy) acetic acid (MCPA) can be used to retard the development of wheat tillers if applied to winter wheat in the fall prior to the initiation of tiller primordia. Fall applications of 0.5 kg ha−1 MCPA were sufficient to reduce the tillering rate by 20–30% while providing a slight, but statistically non-significant, increase in yield. Significant increases in kernels spike−1 were observed in the MCPA treatments. The effect of MCPA on kernels spike −1 could be modulated by nitrogen fertility and planting density. A linear relationship between spike number m−2 and planting density could be observed with MCPA treatments. Reductions in total number of spikes m−2, but an increase in kernels spike−1, resulted in significant improvements in tiller synchrony. Improved tiller synchrony is important in optimizing chemical treatments where applications are based on the developmental stages of the spike. Significant reductions in plant height and subsequent reductions in lodging under high nitrogen fertility and high plant populations were observed with MCPA treatments.