Questions and Answers:
Concerning the Release of a Scale insect to Attack Strawberry Guava

The following answers were taken directly from the text of the Draft Environmental Assessment submitted by the USDA Forest Service, March, 2008. THESE ARE ACTUAL QUOTATIONS FROM THE RESEARCHER PROPOSING THIS INSECT RELEASE.

1. What will the scale insect do to the strawberry guava?
"T. ovatus appears to cause substantial damage to strawberry guava in Brazil. Heavy infestations have been observed to cause defoliation and appear to reduce fruit production. The biological control agent T. ovatus is expected to reduce impacts of this tree by slowing its growth and spread in native forests."

2. How much is known about this scale insect?
"There are very few records pertaining to T. ovatus and its biology in the literature. There have been very few studies of this group of insects, none of them recent."

3. What will the insect to do other plant species?
"Indirect impacts on nontarget species have been documented in a few cases of weed biocontrol, but unfortunately the ability to predict such effects remains poor."

4. What will happen to wildlife when the waiawi fruit is no longer available?
"A variety of non-native species utilize strawberry guava fruit seasonally, and all of these species can be expected to be impacted negatively to varying degrees. Pigs, which feed heavily on strawberry guava fruit when it is in season, may be forced to find other food sources in the short term and may experience reduced population growth in the long term."

5. Waiawi was used 100 years ago by forestry officials to prevent soil erosion, and many roadways are lined with waiawi. If the insect attack is faster than expected, as has happened with the wiliwili , what will this do to the roads, gulches, and other areas vulnerable to soil erosion?
"If strawberry guava were removed suddenly and extensively from steep, wet areas without being replaced by other species, catastrophic erosion could ensue." "[t]here is undoubtedly significant positive value in the protection P. cattleianum (strawberry guava) currently affords to watershed areas. In heavily invaded areas of Hawaii, large monospecific patches of P. cattleianum are now the primary soil-holding species, and these patches often occur on steep slopes in areas with high rainfall." (Taken from Petition for field release of Tectococcus ovatus (Homoptera: Eriococcidae) for classical biological control of strawberry guava, Psidium cattleianum Sabine (Myrtaceae), in Hawaii. May 10, 2005)"

6. What else might happen when the insect is released?
"In some areas, strawberry guava may tend to be replaced by other invasive species over time. Himalayan raspberry, fayatree, and kahili ginger are examples. Other invasive species may benefit from increased light availability within declining patches of strawberry guava. For example, palm grass and other invasive grasses that flourish in high-light forest gaps may increase within stands of strawberry guava that may be partially defoliated by T. ovatus."

7. What could happen when alien grasses move in where the waiawi has lost leaves?
"Although fires are very uncommon in the wet forests where strawberry guava is mainly distributed, increases in grass density could lead to increased risk of wildfires during occasional dry periods. Wildfires are recognized as highly detrimental to Hawaiian ecosystems, because they eliminate native species and perpetuate systems dominated by fire-adapted alien grasses."

8. Will the insect stay on the waiawi, or could it adapt to attack other species?
"Once a biological control agent such as T. ovatus is released into the environment and becomes established, there is a slight possibility that it could move from the target plant (strawberry guava) to attack nontarget plants. If other plant species were to be attacked by T. ovatus, the resulting effects could be environmental impacts that may not be easily reversed."

9. How long might it take for the insect to start attacking other species of plants?
"The timescale expected for T. ovatus to evolve the ability to use a new host plant is difficult to evaluate because its relatives are so few and poorly known. Past experience with agents for biocontrol of weeds indicates...that evolution of ability to use host plants in new, unpredictable ways does not occur very rapidly (over times as long as several decades) (Pemberton 2000). Environmental consequences of such evolution would be largely unpredictable and may not be easily reversed."

10. What are some of the related species that might be threatened by the insect?
Species related to the strawberry guava include the table guava, o'hia, mountain apple, Surinam cherry, jaboticaba, rose apple, java plum, koa, rambutan, longan, eucalyptus, and more. The list includes native and non-native species, some endangered. (Taken from table in Environmental Assessment.)

11. How will the insect spread?
"Movement of T. ovatus following release in the environment is difficult to predict. Populations of the insect are expected to disperse gradually from release sites, mainly carried by wind. In addition to purposeful releases on strawberry guava, unintentional dispersal of T. ovatus may occur by transport of the tiny insects by humans, most likely on infested strawberry guava plants. The ease of transporting T. ovatus on infested foliage makes unapproved distribution of the insect within the Hawaiian Islands a significant risk that may not be adequately controlled under existing quarantine procedures. Therefore, release of this biological control agent at even one site in Hawai'i should be considered equivalent to release over the entire area of the state in which strawberry guava occurs and in which the climate is suitable for reproduction and survival of the insect."

12. How certain are scientists about the eventual impact of this insect attack?
"Environmental impacts of T. ovatus release are expected to occur gradually over a period of decades. There is uncertainty associated with the eventual impact of T. ovatus on strawberry guava. Although observations in Brazil and laboratory tests indicate that this agent can significantly impact individual strawberry guava plants, it may not reduce strawberry guava populations to desired levels or in all areas of Hawai'i. Worldwide, biological weed control programs have had an overall success rate of 33 percent. Actual impacts on strawberry guava by T. ovatus will not be known until after release occurs and post-release monitoring has been conducted."

 
Conclusion:

Benefit of releasing the insect:

  1. Slow the spread of the waiawi by severely reducing its fruit production.

Costs of releasing the insect:

  1. Loss of use of this valuable resource for food and fuel.
  2. Reduced wildlife and wild food, impacting on hunting and gathering rights.
  3. Increased fire and soil erosion hazards.
  4. Replacement of waiawi by other invasive plants.
  5. Threat of this scale insect attacking other species.
  6. Turning hundreds of thousands of acres of healthy waiawi into hundreds of thousands of acres of ugly, sick, fruitless waiawi.
  7. Unwanted waiawi will still need to be removed mechanically.
  8. Property owners with waiawi will need to spray or remove infested plants, creating a liability for the government in covering the property damage caused by this insect.