Complacency lets pests get a headstart
Insects which may at first not give growers much concern can turn out to be a major menace.
Learning from other countries’ experiences when it comes to biosecurity can better prepare this country’s growers, Nuffield Scholar, Simon Cook, believes. He’s recently been travelling in the United States looking at a range of insect pest incursions and how they’ve been handled.
He’s a third generation kiwifruit grower from Te Puke and first visited a large kiwifruit orchard near Auburn in Alabama where one of the major challenges is dealing with Brown Marmorated Stink Bug (BMSB). A number of the techniques discussed locally as possible management plans if there is an incursion have been used with one was the use of bait plants to lure BMSB out of the kiwifruit so more toxic sprays could be used. But that would cause residue problems and in this case it’s not successful as the bugs prefer to stay in the kiwifruit. The next strategy to be tried is the use of chemical impregnated cloth with bright lights shining on it at night to try and attract BMSB. It was being trialled with limited success elsewhere, but there is significant risk of off-target deaths. So far the most successful method has been the use of baited traps that are regularly capturing hundreds of bugs. Trissolcus japonicas, the Samurai Wasp is not present.
“A large factor in the reduction of the population was being credited to the presence of the Samurai Wasp.
“When I got to Pennsylvania later in my trip I found the populations of BMSB that initially had exploded in that area were now heavily reduced and BMSB was not considered as significant as it had been,” he said.
“A large factor in the reduction of the population was being credited to the presence of the Samurai Wasp.
▶ Clint Wall, who worked for Seeka in New Zealand as a kiwifruit technical rep before moving home to Auburn Alabama where he has setup a 100 hectare trial kiwifruit orchard in partnership with Californian company Sun Pacific.
▶ Huanglongbing (HLB) which literally translates to yellow dragon disease in China “In China BMSB is not a major problem because the Samurai wasp has developed as a natural control to keep its numbers in check. When BMSB is moved to a new environment with no natural predator or natural control, then there is nothing to stop its numbers expanding to plague proportions. This is the real risk with biosecurity incursions where you can get the pest without its corresponding biocontrol and a pest which at home can seem rather benign suddenly can explode in numbers and cause major problems to industry.
“This can also cause problems identifying what our real threats are in terms of invasive species as in their home countries that quite often are not an issue. In China Yellow Spotted Stink Bug (YSSB) has more of an impact on agriculture than BMSB.”
Next he visited Florida where Citrus Greening disease, or Huanglongbing (HLB) which literally translates to yellow dragon disease in China, appeared.
“The first sign of a coming problem with HLB was the arrival of the Asian citrus psyllid, a well known vector for the transmission of the disease. For four years they battled the psyllid incursion without success keeping a close eye out for the first sign of HLB. The psyllid itself does very little damage, and growers started to become complacent towards the management of the psyllid, which is very difficult to control.
“This all changed with the first positive identification of HLB in an orchard in Florida. Interestingly talking with a grapefruit grower, this still did not concern them as they mistakenly believed it would not affect them.
“Since the incursion around US$250m has been invested in research to try and overcome the incursion with little success. Whilst waiting for some solution growers find themselves very much in survival mode unsure of their future. Many growers have been forced to abandon orchards or cut them out and look at trying to grow some other crop instead of citrus. I saw a number of orchards that once produced citrus now growing blueberries, watermelon, onions, basically trying anything they can think of to survive. >
“The most likely solution to allow the industry to survive will be the breeding of new tolerant varieties, most likely created using some kind of genetic modification.”
“The most likely solution to allow the industry to survive will be the breeding of new tolerant varieties, most likely created using some kind of genetic modification. Without the use of genetic modification it’s unlikely a new tolerant variety will be bred anytime soon. Natural selection breeding typically takes around 20 years to deliver new solutions – I’m not sure the industry can wait that long.
“Whilst I understand why New Zealand farmers and growers have been fighting to be GM-free with all the pressure being exerted in our major European markets, I can’t help thinking this decision may be short sighted and potentially expose them to greater risk at some time in the future. If biosecurity is the number one risk facing the agricultural industry in NZ is genetic modification in all its forms, potentially our number one solution?
“This also brings me to Kauri dieback. If we are unable to control the spread of the Phytophthora causing this disease then will we be left with the options of losing Kauri all together, or using GM technology to modify the existing genes within Kauri’s DNA to enable it to develop resistance. Are we better to have a GM Kauri than no Kauri at all?”
He then made his way north to West Virginia to meet Dr Tracy Leskey of the United States Department of Agriculture (USDA), to catch up on their latest research into the control of BMSB, and in particular the work they were doing with the Samurai Wasp. > “BMSB is thought to have first been seen in the US in 1995-96 however it was not formally identified until 2001 in Allentown Pennsylvania,” he said. “When it arrived there were 25 other Pentatomidae or shield/stink bugs species already native to the US. One more was not considered to be a problem and it was assumed the natural controls already regulating the other Pentatomidae species would also preditate BMSB and keep its numbers under control.
“The first indications all was not well came in 2008-2009 from apple growers who started to notice caulking in their fruit. The only response at their disposal was to increase the number of hard chemical sprays they were applying. The average grower went from using insecticides four to five times a year in 2010 to 10-15 in 2011. This had the unintended consequence of knocking out several beneficial insects that in turn created further problems.
“Once researchers in the US were aware of the threat that BMSB posed, they began looking at potential control measures with the most obvious one being the Samurai Wasp. The US had begun the process of investigating the import and release of the wasp when it was discovered already in the country in small numbers. Since then the focus has been on breeding and releasing greater numbers of Samurai Wasp to bring the BMSB population under control, which it does now seem to be.
“It was interesting that when I visited growers in this area, BMSB was no longer considered a major threat. Damage in orchards whilst still present, has dropped from up to 90 percent fruit-loss to less than five percent. This was fantastic news as it certainly indicated that some level of control was being achieved that we could learn from.
“No one would guarantee the Samurai Wasp is the cause for the decrease in BMSB numbers, however it is strongly suspected but there may also be other factors not fully understood yet.
“In its home, China, BMSB is not a major pest to agriculture, in fact the yellow spotted stink bug is considered a greater pest. A natural predator keeps BMSB numbers in check as nature seeks to maintain a balance. When you take BMSB out of China without its natural predator to keep it under control, then its numbers can explode to plague proportion causing significant damage as we saw in the US in 2010-2015.”
On his final day in this area he was looked after by Mark Sutphin, an extension agent with Virginia Tech who took him to the town of Winchester to have a look at the Spotted Lanternfly
This is the real risk with biosecurity incursions where you can get the pest without its corresponding biocontrol and a pest which at home can seem rather benign suddenly can explode in numbers and cause major problems to industry.
(SLF), Lycorma delicatula incursion there.
“It was first noticed in Pennsylvania in around 2015,”he said.
“The initial incursion is thought to be from egg masses that had been laid on paving stones in China and then imported to the US. From the initial site they forward traced any movements of stone to a paving stone depot in Winchester Virginia. For two years they continued to monitor the site with no sign until the first SLF were observed two years later. There is no known pheromone or aggregation traps for SLF so the only method of finding them is visual observation and sticky tape attached to trees.
“One of the keys to finding SLF is the presence of Ailanthus altissima or the Tree of Heaven as it is commonly known. Ailanthus was imported from China as a decorative tree but has now spread widely throughout the US and is considered a pest plant. SLF seem to focus heavily on populating Ailanthus as mature adults around the time they breed. It is not known if the plant plays an important role in this process or is just a preference at this stage. During previous lifecycle stages as a crawler SLF has been observed feeding on over 70 different plant species, the only plant it has so far not shown an interest in feeding on is conifers. This is where part of the danger in this pest lies, its ability to happily feed on a wide range of host plants. “To be honest I wasn’t overwhelmed by what I was looking at, rather I viewed this incursion that for two years had not moved more than a mile, as being relatively easy to eradicate. It wasn’t until I spent time in Pennsylvania where the incursion is far greater that I really got a feel
It prefers to lay its eggs on trees when numbers increase it will lay its eggs anywhere. Egg masses have been seen on stone, timber palings, rusty metal – basically anywhere, and this is where the real risk of SLF being spread comes. “I came away with the feeling that if you could identify an incursion early enough, and were prepared to go hard at it, then there was every chance you could successfully eradicate a SLF incursion in NZ.”
for the threat this insect could pose. Lanternfly is not difficult to kill and if you had sectioned of all the affected properties and railroad area in Winchester, sprayed it with something reasonably toxic, then I believe it would be relatively easy to eradicate.
“This highlights one of the crucial advantages we have in dealing with an incursion, the powers the Ministry for Primary Industries (MPI) are given under the Biosecurity Act 1993. I didn’t really appreciate the importance of this legislation and how vital it is to our success in dealing with incursions until I spent time in the US. “In the US the Federal Authorities have almost no powers and the State only has a little more. The Federal and State Authorities can ask the homeowners permission to carry out activities on their property but have no way of forcing the homeowner to comply. So in the middle of an incursion you can have a homeowner refuse to cooperate and thereby creating a reservoir to re-infect treated neighbours, making eradication all but impossible.
“SLF on its own cannot travel far. During its instar or crawler phases of which there are four, it looks to climb the nearest tree or object. It will tend to fall of a structure and then look to climb back up. In its adult form it can fly but is more of a hopper and will only fly very short distances and on its own won’t travel far. The real risk is that whilst it prefers to lay its eggs on trees when numbers increase it will lay its eggs anywhere. Egg masses have been seen on stone, timber palings, rusty metal – basically anywhere, and this is where the real risk of SLF being spread comes.
“I came away with the feeling that if you could identify an incursion early enough, and were prepared to go hard at it, then there was every chance you could successfully eradicate a SLF incursion in NZ. The real risk is not finding it in time because once established, the wide host range could mean SLF is unstoppable. At this stage there is still no known natural predator and the primary control being used is injecting a systemic neonicotinoid Dinotefuron into Ailanthus trees killing SLF after they feed.
“When SLF feed as an instar or adult they suck phloem sap from trunks stems and leaf petioles. SLF feeding in large numbers can be severe enough to cause shoot dieback and, in some cases, plant death. One grape grower had reported the plants that had seen heavy feeding in spring had not been able to survive winter dormancy. Heavy feeding on hops has also been seen with buds being tainted by the feeding leaving them unable to be used for production of beer.
“Whilst it is feeding the SLF also produces large volumes of honey dew that can result in significant levels of sooty mould.
“It wasn’t until I headed back up to Pennsylvania and the city of Reading which is at the centre of the SLF incursion there that I really started to get an understanding of the threat this insect poses. It has now spread across 60 counties in Pennsylvania and covers an area of 6,000 square miles. While I was in the US the first sightings in New Jersey were announced meaning it had now spread to three states. In South Korea within three years of first being identified it had spread throughout the country.
It has now spread across 60 counties in Pennsylvania and covers an area of 6,000 square miles.
“I visited The Pagoda in Reading which sits on top of a hill and has one of the worst infections in the
surrounding park. All around and over the Pagoda were significant numbers of SLF. As I was walking back down a hill I noticed from a distance the grass around one of the trees was shiny from honey dew. As I got closer I could also see the base of the tree was black from sooty mould. Standing under the tree it felt like there was a soft drizzle and looking up you could actually see the honey dew being secreted, such was the volume.
“Not only will this pose major problems in terms of sooty mould, but the large volume will potentially provide a significant food source for wasps. “I left that area and headed
10km away. I had to stop for gas and as I was standing there filling up the car I noticed several SLF just hanging out on the petrol pump. It was then I started to understand the difficulty faced controlling this pest once it started to spread.
“A few days later I attended a meeting on SLF run by Pennsylvania Secretary of Agricultural Russell Redding and Penn State Universities Dean Rick Roush. Both originally trained and worked as entomologists and in Pennsylvania both have dealt with the incursions of BMSB, Fruit Fly, Spotted Wing Drosophila and now SLF. Roush made the comment during most damaging and greatest threat to agriculture of all the invasive pests he’s seen. This was a pretty sobering comment and reinforced the threat this insect poses.”
I noticed several SLF just hanging out on the petrol pump. It was then I started to understand the difficulty faced controlling this pest once it started to spread.
Next Simon will look at Banana Panama disease in Queensland, Fruit Fly in the South of Australia and the BMSB incursion in Santiago, Chile.
“It’s thought that the most likely spot for an incursion to occur in NZ is in an urban area, so what is happening in Chile is of particular interest.”
▶ Multiple fourth instar spotted lanternfly congregating in numbers on a shoot. ▴ Two stages of lanternfly with the single one an adult female spotted lanternfly.
◀ The blackness created by sooty mould and shining on the grass leaf is honey dew secretion from lanternfly. A wasp can be seen feeding on the honey dew which is a food source and could result in increased numbers.
▶ Ben Hayes of Hayes Farms, Culman County, Alabama.