Research

Arthropods of Agricultural Importance With the world population projected to increase to > 9 billion by 2050 [1], production of food in a cost effective and environmentally sustainable manner is a high priority. A doubling of current food production will be required [2]. However, an estimated 10-20% of major crops worth billions of dollars are lost to herbivorous insects, representing a major constraint to achieving this goal. In addition, post-harvest losses resulting from insect and mite-associated damage of stored food, cause estimated losses of 30% valued globally at over one hundred billion U.S. dollars [3, 4]. Within the United States, the management of a single pest species, the soybean aphid, which decimated soybean production in the North Central region, has cost an estimated $1.6 billion over a ten year period [5].

Arthropods of Medical Importance Arthropods negatively impact human health and welfare through infliction of injury and transmission of disease. Bed bugs are of significant public health importance with the recent resurgence of bed bugs attributed in part to increased international travel and resistance to multiple pesticides [6, 7]. Bed bugs have caused considerable economic loss to the hotel industry through lawsuits and loss of business, with costs to hotels in New York City estimated at $7,700 per room per year in lost revenue and extermination.

Mosquito-vectored dengue virus and malaria have spread rapidly during the last decade into highly populated urban areas resulting in a dramatic rise in the numbers of clinical cases [8, 9]: There are some 50 million dengue hemorrhagic fever infections per year resulting in 500,000 hospitalizations [10], and 250 million cases of malaria per year, leading to some 1 million deaths worldwide [11, 12]. An estimated $2 billion was spent on malaria control in 2011. Costs associated with morbidity are massive. Vector control is one of the most effective strategies used to prevent the spread of mosquito-borne diseases [5]. In the United States, mosquito-transmitted West Nile virus [13] and tick-transmitted Lyme disease [14] are the primary arthropod vectored disease concerns for public health officials.

Arthropod Management and Current Research Needs

The use of classical chemical insecticides was a major contributing factor to the increase in agricultural productivity in the 20th century [15] and insecticide application remains the primary management practice for the majority of arthropod pests. There are a number of disadvantages associated with their use including development of resistance by pest populations, deleterious impacts on non-target organisms, bioaccumulation in the food chain, environmental pollution and potential effects on the health of humans [16]. Hence, there is ongoing pressure to develop target-specific, environmentally-friendly and biodegradable pest management tools.

Repeated application of chemicals invariably results in the development of insecticide resistance in the targeted pest, with more than 500 species of insects and mites with insecticide resistance recorded, including vectors of human disease [4, 17-19]. As a result, chemicals that were effectively employed in the past are no longer useful against many pest species. Insecticide resistance mechanisms are highly diverse and include enhanced metabolism by detoxifying enzymes, target site insensitivity, reduced insecticide penetration and increased excretion [20-35]. There is a pressing need to find new approaches to manage pests that are resistant to classical chemical insecticides.

Pest tolerant transgenic plants provide a more sustainable approach for crop protection. Toxins derived from the bacterium, Bacillus thuringiensis (Bt), have been highly effective for the management of lepidopteran (moth) and coleopteran (beetle) pests when delivered by transgenic plants [36-39]. Indeed, since their initial introduction in the early 1990s, transgenic plants have been widely adopted [38], with 65% of corn and 73% of cotton planted in U.S. in 2011 expressing Bt toxins [40]. As a result, pesticide use and crop production costs have both been reduced [41-43]. However, resistance to Bt toxins has been documented [44-46] and Bt toxins are not sufficiently toxic for management of the sap-sucking, hemipteran pests [47]. In some cases, the reduced application of chemical insecticides on Bt crops has resulted in increased populations of hemipteran pests [48-51]. Greater flexibility is needed for in planta expression of insecticidal constructs such as Bt toxins, including tissue specific expression, protein and transcript stability. In addition, training of personnel with knowledge of hemipteran pests will be essential for the needs of industrial partners seeking to deal with this emerging group of primary pest arthropods.

In many organisms including insects introduction of double-stranded RNA (dsRNA) results in the specific inactivation of an endogenous gene with sequence identity to the introduced dsRNA; this process is known as RNA interference (RNAi) [52]. RNAi has potential for developing target-specific management methods for insect pests. Injection of dsRNA down-regulates the expression of genes in many insect species [53-60], and the practical application of this approach for arthropod control has been demonstrated [55, 61-63]. However, research is needed to delineate factors that limit the current application of RNAi to certain arthropods to fully exploit the potential of this new approach.

There is an urgent need for development of pest control tools with new target sites. Recent advances in the development of genomic and post genomic technologies provide enhanced means for identifying target sites and for screening assays to rapidly identify chemicals that function through newly identified target sites.  A target site must satisfy several criteria to be acceptable for screening assays:

1. The target site should be necessary for pest survival, present most of the time and respond quickly to intervention leading to death of the pest insect;

2. The presence and functionality of the identified target site in non-targets including beneficial insects, animals and humans should be assessed;

3. The identified target site should have screening potential and be amenable to high throughput screening;

4. The potential for development of resistance to the identified target site should be considered. 

Due to the magnitude of economic loss associated with arthropods and the propensity for arthropods to develop resistance to management strategies in current use, there is a critical need for industry to provide arthropod management products with novel modes of action. However, in many cases, there is insufficient understanding of the basic biology of the pest organisms to provide a foundation for such innovative technological solutions.

Research conducted within the Center falls within five areas of emphasis:

1) Pest tolerant transgenic plants

2) RNA interference

3) Insect resistance

4) Novel target sites

5) Methods.

 

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