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United States Department of Agriculture

Agricultural Research Service

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Robert Hollingsworth
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Robert Hollingsworth

Contact Information

U.S. Pacific Basin Agricultural Research Center
64 Nowelo St.
Hilo, Hawaii 96720 
Ph: (808) 959-4349
Fax: (808) 959-5470


via ARIS System

via Google Scholar


  • Ph.D., Entomology, North Carolina State University, 1990
  • M.S., Agriculture and Pest Management, North Carolina State University, 1982
  • B.S., Biology, Davidson College, Davidson, NC, 1980

Professional History

1998 - Present

Research Entomologist, U.S. Pacific Basin Agricultural Research Center, USDA-ARS, Hilo, Hawaii (USA)


United Nations Fruit Fly Entomologist, Dodo Creek Research Station, Honiara, Solomon Islands


Research Associate, Entomology Department, University of Arkansas, Fayetteville (USA)


Post-doctoral Research Fellow, Entomology Department, University of Hawaii, Honolulu (USA)


Entomologist, Lowlands Agricultural Experiment Station, Keravat, E.N.B.P., Papua New Guinea


Research Assistant, Entomology Department, North Carolina State University, Raleigh (USA)


U.S. Peace Corps Entomologist, Western Samoa Department of Agriculture, Apia, Samoa


Research Accomplishments

I have worked in the fields of entomology and pest management over 28 years doing research, extension, and project management. I have worked in developing countries in the Pacific Basin, including Samoa, Papua New Guinea, and the Solomon Islands where I studied the coconut rhinoceros beetle, tephritid fruit flies and various species of slugs and snails. Since joining ARS in 1998, I have studied control methods for various pests of ornamental crops (especially thrips). I am now working on field control methods for a new pest on coffee: coffee berry borer.

Discovered caffeine as a control for slugs and snails

Unlike the situation with insects and insecticides, there are only a handful of active ingredients used in pesticides designed for slugs and snails. Even these are relatively ineffective, frequently killing less than half of the pest population each time treatment is applied. Drench treatments of caffeine have been used in Hawaii to control an invasive frog species (the coqui) and prevent its spread to other islands. Researchers noticed that slugs were affected by these treatments. Following up on this observation, we discovered that caffeine was very effective as a repellent and toxicant for slugs and snails. A series of laboratory and greenhouse bioassays demonstrated that caffeine solutions controlled small snails infesting potted orchids better than a liquid formulation of metaldehyde (the industry standard) while caffeine drenches killed or repelled large slugs infesting plant pots.

Cuban slugs on Napa cabbage dipped in caffeine solutionsCuban slugs feeding on Chinese cabbage

Left: feeding by Cuban slugs on Napa cabbage dipped in caffeine solutions (0.1 to 1.0% caffeine).

Right: Cuban slugs feeding on Chinese cabbage.

Studied pest status and diversity of fruit flies in the Solomon Islands

Tephritid fruit fly species are major quarantine pests of fresh fruits and vegetables, preventing or limiting their export to other counties. The native fruit fly fauna is naturally diverse in the Solomon Islands, and about 50 species have been identified from this region. For most of these species, the natural host plants are unknown. Over a 2?-year period, I coordinated a research program which included trapping, host fruit collection, fruit fly rearing, host-status experiments and heat-tolerance tests of fruit fly eggs and larvae.

Solomon Islands lie between Papua New Guinea and VanuatuThe mango fly, Bactrocera Frauenfeldi, is the most important fruit fly pest in the Solomons

Left: the Solomon Islands lie between Papua New Guinea and Vanuatu.

Right: The mango fly, Bactrocera frauenfeldi, is the most important fruit fly pest in the Solomons.

Developed sampling information for thrips in orchids

Cut Dendrobium orchid flowers produced in Hawaii are valued at $2.5 million per year. Thrips are the most important insect pest limiting the export of these flowers. They are difficult to see in blossoms, yet a single thrips found by a quarantine inspector can result in rejection of the entire shipment, meaning that the flowers must be sent back or destroyed. We studied distributions of thrips within commercial plantings. A Monte-Carlo nearest-neighbor analysis of sample data showed that thrips were randomly distributed regardless of the distance separating samples. This knowledge simplifies sampling protocols. In addition, we determined that flower shaking was a more efficient method for detecting adults than using Berlese funnels.

Left: Dendrobium orchids grown for cut flowers.

Middle: Thrips palmi damage on Dendrobium orchids.

Right: Dichromothrips smithi on bamboo orchids.

Documented pest status of slugs and snails in the Pacific Region and developed solutions

The importance of slugs and snails as direct pests of agriculture and as quarantine pests in the Pacific region has been underestimated because slug and snail damage is frequently attributed to other causes. In addition, the identification, biology and distributions of pest species are poorly documented. We studied the biology and pest status of the orchid snail and discovered that these small snails caused serious damage to orchid roots even when only one or two snails were present in a 4-inch pot. Because snails hide within the potting medium, some growers had been attributing the damage caused by snails to root rot pathogens, while others wrongly supposed snails were being introduced within new bags of commercial potting media. We discovered that none of the commercially available molluscicides were very effective against orchid snails, yet snails could be effectively controlled by repeated applications of the best-performing chemicals spaced 3-4 weeks apart.

The orchid snail (Zonitoides arboreus) with eggs

Above: The orchid snail (Zonitoides arboreus) with eggs.

In 2005 in cooperation with the Centers for Disease Control and Prevention (CDC), we carried out a survey for a new semi-slug species (Parmarion martensi) which was abundant around homes and gardens in east Hawaii island. We found that this species was not a serious agricultural pest, but posed serious disease risks for humans due to its behavior and propensity to vector a nematode species.

Parmarion martensi on a tree orchid

Parmarion martensi on a tree orchid.

During 2004-2006, working with USDA-APHIS malacologist Dr. David Robinson, we carried out slug/snail surveys in Hawaii and other Pacific islands documenting pest problems and distributions, raising awareness regarding the pest status of slugs and snails, and training others how to prevent the spread of these quarantine pests.

Tested treatments and procedures to reduce to risk of bringing in pest species with Christmas trees

Each autumn, hundreds of sea-freight containers filled with Christmas trees are imported into Hawaii from the Pacific Northwest. These imports are a risk for the accidental introduction and establishment of new yellowjacket species and other insect pests. Working with scientists at the Hawaii Department of Agriculture, the University of Hawaii and Washington State University, we studied the efficacy of shaking treatments and demonstrated the effectiveness of pre-harvest pyrethroid spray applications for control of yellowjacket queens and other pests in Christmas trees. This cooperative research project showed that current quarantine protocols were inadequate, and generated new data demonstrating the potential of using pre-harvest sprays of pyrethroid insecticides as a risk mitigation procedure. Beginning in 2008, quarantine protocols involving tree shaking procedures were made more strict.

Professor Gary Chastagner of WSU shaking insects from a Christmas tree

Professor Gary Chastagner of WSU shaking insects from a Christmas tree.

Developed improved formulations of essential oils for insect control

Mealybugs and scales are important quarantine pests which impede international trade of fruits, vegetables and ornamental plants. They are difficult to control with conventional contact insecticides because of the water-repellent waxes that cover their bodies. Hydrocarbon chemicals such as limonene and other terpenes found in plant essential oils soak through the wax coatings of these insects and kill them. However, plant oils are phytotoxic to plant leaves unless they are properly emulsified in water. In the process, the insect-killing ability of these terpene chemicals can be lost. We developed aqueous, plant-safe and effective emulsions of essential oils and terpene components for control of waxy insects using food-safe ingredients, and are carrying out research to further improve formulations.

Solution of citrus peel oil washes away the white wax covering the mealybugs

Immediately after being sprayed with a solution of citrus peel oil, the white wax covering the mealybugs starts to wash away.

Service, Leadership and Participation in Professional Activities:

  • Entomological Society of America (Chair, Regulatory Section 2003; Chair, International Affairs Committee 2007)
  • Hawaiian Entomological Society (Vice-president, 2003-2004; President 2004-2005)
  • Initiated annual Big Island Insect Count (Youth Activity) 2004.
  • Initiated and presented PBARC's award for an Outstanding Research Project in Agriculture in the Hawaii State Science & Engineering Fair, 2002-2011
  • Provided trainings on the identification and control of exotic slug and snail species to government workers and researchers in Samoa, American Samoa and the Federated States of Micronesia, 2005-2006.
  • Helped develop Pest Management Strategic Plans for Orchids (2010) and Christmas trees (2009).

Honors, Awards, Achievements and Recognition:

  • Member, Sigma Xi, Scientific Honorary Society
  • Fulbright Fellowship to Papua New Guinea, 1990
  • Affiliate Graduate Faculty Member, University of Hawaii at Manoa
  • Invited Professor, INRS-Institut Armand-Frappier, Laval, Quebec
  • ESA Distinguished Achievement in Horticultural Entomology, Pacific Branch, 2011

Last Modified: 8/11/2016
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