L. T. Wilson

Invasion by the Variegated Leafhopper and Biotic Interactions: Parasitism, Competition, and Apparent Competition

In 1980 the variegated leafhopper (VLH), Erythroneura variabilis, invaded Californias San Joaquin Valley, and has since rapidly increased in numbers to become a major pest in vineyards. Correlated with the invasion by VLH are declining populations of the congeneric grape leafhopper (GLH), E. elegantula. This paper explores interspecific competition and shared parasitism as possible reasons for this decline in GLH. Although interspecific competition between VLH and GLH was evident in field-cage experiments, its effects were equivalent to intraspecific competition. Instead of simple direct competition explaining the replacement of GLH by the invading VLH, the key appears to be a parasitoid that is shared by the two leafhoppers. In particular, the native GLH experiences higher attack rates from the shared parasitoid (Anagrus epos) than does the invading VLH. This differential parasitism apparently shifts the competitive balance from one of equality to a strong disadvantage for the native relative to the invader. This is the first study, to our knowledge, to document the importance of parasitoid-mediated indirect effects in an in- vasion.

Food security and climate change: on the potential to adapt global crop production by active selection to rising atmospheric carbon dioxide

Agricultural production is under increasing pressure by global anthropogenic changes, including rising population, diversion of cereals to biofuels, increased protein demands and climatic extremes. Because of the immediate and dynamic nature of these changes, adaptation measures are urgently needed to ensure both the stability and continued increase of the global food supply. Although potential adaption options often consider regional or sectoral variations of existing risk management (e.g. earlier planting dates, choice of crop), there may be a global-centric strategy for increasing productivity. In spite of the recognition that atmospheric carbon dioxide (CO2) is an essential plant resource that has increased globally by approximately 25 per cent since 1959, efforts to increase the biological conversion of atmospheric CO2 to stimulate seed yield through crop selection is not generally recognized as an effective adaptation measure. In this review, we challenge that viewpoint through an assessment of existing studies on CO2 and intraspecific variability to illustrate the potential biological basis for differential plant response among crop lines and demonstrate that while technical hurdles remain, active selection and breeding for CO2 responsiveness among cereal varieties may provide one of the simplest and direct strategies for increasing global yields and maintaining food security with anthropogenic change.

Pheromone blends of green stink bugs and possible parasitoid selection.

It is confirmed from a literature review and new research that different pheromone strains exist in Nezara viridula from different geographical regions and that males from the sister genus Acrosternum emit bouquets of distinctive ratios of the same sesquiterpenes as in N. viridula. Many tachinid parasitoids use heteropteran pheromones as kairomones, and it is suggested that the chemical similarity of pheromones of N. viridula and Acrosternum has facilitated the adoption of N. viridula as a host by tachinids in the New World.

Diel and seasonal variation in CO2 flux of irrigated rice

Abstract Rice is a primary food source for half the world’s population, but little is known of how temporal changes in the field-scale physical environment affect carbon dioxide exchange rate (CER), biomass accumulation, and crop yield. Experiments were conducted in 1998 and 1999 in a commercial field near El Campo, TX, to evaluate interactions between CER and the physical environment. Tower-based conditional sampling was used to measure CER. Environmental parameters such as photosynthetically active radiation (PAR), net radiation, and temperature were measured along with CER. Whole-plant biomass was also collected throughout both seasons. Fluctuations in diel CER were correlated with changes in PAR, while season-long trends in CER were associated with changes in leaf area index and stage of development. Crop yield was found to be directly related to total carbon-dioxide exchange after heading, and may have been affected by environmental conditions at anthesis, such as temperature and wind speed, or leaf nitrogen status, both of which differed considerably between the two seasons. Data showed a positive correlation between biomass accumulation and cumulative CER for both years of the study.

Predicting economic losses from the continued spread of the Mexican rice borer (Lepidoptera: Crambidae).

Abstract The Mexican rice borer, Eoreuma loftini (Dyar) (Lepidoptera: Crambidae), is an invasive species that originated from Mexico, and it is threatening to cause major economic losses to sugarcane, Saccharum spp., and rice, Oryza sativa L., industries in Louisiana. The insect is expected to reach sugarcane and rice production areas in Louisiana by 2008, and infest all of Louisiana sugarcane and rice industries by 2035. When all sugarcane in Louisiana becomes infested, annual yield losses of

Role of oviposition preference in an invasive crambid impacting two graminaceous host crops.

220 million would be expected for a cultivar of comparable susceptibility to LCP 85-384 (assuming this cultivar is planted on 100% of the production area). This also assumes the use of the current practice of rainfed production and one application of insecticide, which is presently used by farmers in Louisiana. Irrigation with 30 cm of water is predicted to reduce estimated losses by 29%, whereas four applications of a biorational insecticide such as tebufenozide are expected to reduce the loss in revenue by 53%. The use of the resistant ‘HoCP 85-845′ would reduce the projected loss in revenue by 24%. Combining all three management tactics on sugarcane, anticipated net loss in revenue would decrease by 66%. The rice industry in Louisiana is projected to suffer from a loss in revenue of

A food-web approach to economic thresholds: A sequence of pests/predaceous arthropods on California cotton

45 million when the entire state is infested. A 77% reduction in loss in revenue is expected with one application of lambda-cyhalothrin. A quarantine on east Texas sugarcane is estimated to save the Louisiana industry between

An ecosystem analysis of spider mite outbreaks: physiological stimulation or natural enemy suppression

1.1 billion and

Computer-based cotton pest management in Australia

3.2 billion (depending on management) during the time needed for the insect to fully invade the state’s sugarcane and rice producing area by natural migration rather than by accidental introduction. The rapid deployment of appropriate management tactics will have a key role in reducing the anticipated economic impact of E. loftini once it becomes a pest in Louisiana sugarcane and rice.

Models for age structured populations with distributed maturation rates

Abstract Oviposition preference studies of the Mexican rice borer, Eoreuma loftini (Dyar), on sugarcane, Saccharum spp., and rice, Oryza sativa L., showed that drought stressed sugarcane was 1.8-fold more attractive based on egg masses/plant than well watered sugarcane. The E. loftini susceptible sugarcane cultivar LCP 85–384 was 1.6-fold more attractive than HoCP 85–845 based on numbers of eggs per egg mass. Egg masses were 9.2-fold more abundant and 2.3-fold larger on sugarcane than on rice. Rice, however, was preferred to sugarcane on a plant biomass basis. Oviposition on sugarcane occurred exclusively on dry leaf material, which increased under drought stress. Egg masses per plant increased on drought stressed sugarcane and were correlated with several foliar free amino acids essential for insect growth and development. The more resistant (based on injury) but more attractive (based on oviposition) rice cultivar XL8 had higher levels of several free amino acids than the susceptible cultivar Cocodrie. The association of host plant characteristics to oviposition preference is discussed. Projected oviposition patterns relative to sugarcane and rice production areas were estimated for Texas and Louisiana based on the availability of each host in different regions of each state. These results suggest that, where sugarcane and rice co-occur, the majority of eggs would be found on sugarcane early in the season, because of this crop’s substantially greater biomass compared with rice. Abundance later in the season would also favor sugarcane; however, the abundance on rice would be greater than expected solely based on host availability, largely because of the greater preference per gram of rice plant dry weight.