Ding Dong Merrily On IPM

Whether you celebrate Christmas or not, this time of year it’s cold and dark and the shops are full of lights and food. But it’s not just farmers and producers we have to thank for Christmas dinners, biological control agents are helping to put food on our table all whilst enabling traditional pesticide use to be reduced. Let’s take a walk through some traditional Christmas fare, their pests, and the solutions available.

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Sprouts

Love them or hate them, sprouts are an iconic part of Christmas dinner and have well-studied pests and therefore require a many-faceted pest management strategy. Intercropping and companion plants can be used to control the cabbage moth (Mamestra brassicae) and the garden pebble (Evergestis forficalis). Intercropping of mustard with the brussels sprout crop reduced levels of the mealy cabbage aphid Brevicoryne brassicae to levels where they can be adequately controlled by predatory syrphid larvae, without reducing sprout yield. Rove beetles (Aleochara spp.) can be used as predators to control the cabbage root fly, Delia radicum, once pest numbers have been reduced to an appropriate level.

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Garden pebble larvae on broccoli

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Mealy cabbage aphid infestation on a Brassica leaf

 

Carrots

It’s important, with all this indulgence, not to forget to leave some carrots out for any reindeer which might be passing this part of Shropshire. One study found that by growing carrot varieties with natural carrot root fly (Psila rosae) resistance, smaller amounts of insecticidescan be used, in turn allowing natural predators and parasitoids to work through the crop. It also found that sowing brassicas underneath the carrot crop can further reduce insecticide usage. This is the perfect example of how integrated pest management strategies can be used to deliver an effective alternative to traditional pesticides to secure sustainable production of my second favourite vegetable (spot the IPM student).

 

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A carrot root fly larvae emerging from an infected carrot

Wine

Port, sherry, Buck’s Fizz, whatever your tipple at Christmas is, if it’s wine-based, the likelihood is it’s made from the European grape Vitis vinifera, which is incredibly susceptible to pests and diseases, not least the Japanese beetle, Popillia japonica, which can feed on all parts of the plant both as a larva and an adult, causing dramatic damage in vineyards. Japanese beetle numbers can be reduced by up to 100% using the nematode worm Heterorhabditis bacteriophora which infect the beetle larvae and release Protorhabdus bacteria which kills them, without affecting non-target organisms in the soil.

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The life cycle of the Japanese beetle

Chocolate

UK residents consume the 4th most chocolate in the world, consuming on average 6.8kg of chocolate in 2015, and Christmas is a peak time for chocolate coins, Toblerone, and Terry’s Chocolate Oranges (not sponsored, sadly). One of the most important pests of chocolate is the cocoa pod borer moth (Conopomorpha cramerella): the larvae tunnel into the pod and feed on the seeds for two to three weeks before chewing their way out of the fruit to pupate. The damage they cause to the cocoa pods causes an enormous economic impact on cocoa industries, especially impacting Indonesia, Malaysia, the Philippines, Papua New Guinea and Western Samoa. The presence of the black cocoa ant (Dolichoderus thoracicus) has been observed to increase the amount of cocoa pod damage seen, with the ants entering previously damaged pods to attack the moth larvae. The presence of the ants also reduces the amount of rat damage normally found on up to 90% cocoa pods, showing the wide-reaching impacts of beneficial invertebrates.

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A cocoa pod showing damage from the larvae of the cocoa pod borer moth

 

Oranges

For many people, a satsuma in the toe of your stocking is a classic feature of Christmas, and even if not, a bit of fresh fruit can really help cleanse the palate as well as bringing a bit of welcome vitamin C in the cold, dark months. The chili thrips, Scirthothrips dorsalis Hood, is a significant pest of tropical fruits and ornamental crops, including causing silver scar damage to satsuma mandarin fruit. Luckily, however, the thrips can be controlled using phytoseiid mites as predators, including Neoseiulus cucmeris and Amblyseius swirskii, with A. swirskii being able to reduce the thrips level to one per leaf, where they’re no longer damaging to the plant.

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Chili thrips damage on rose leaves

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Thrips damage on young oranges

 

All these fun and games aside, it must be remembered that food security is a difficult and ever-changing issue, especially with the growing global population. The work which goes in to developing alternate solutions to traditional chemicals and ensuring that we can enjoy many Christmases to come, is an important facet of modern applied entomology.

Happy Christmas from the EntoBlog gang!

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Britain’s Next Top Pest

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Our Entomology MSc gang have just had two weeks hearing from some of the key players in the biological control industry. While there were many invasive insect pests mentioned that are currently giving UK growers cold sweats in the middle of the night, a few names kept cropping up.

Without further ado, here’s a run-down of just a few of the headline crop-hungry taxa posing new threats on these shores.

Spotted wing drosophila (Drosophila suzukii)

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Not the most appetizing plum, thanks to D. suzukii (photo: Martin Hauser/ Wikimedia Commons)

Despite its catchy name, nobody hopes to catch this fruit fly on their crop. Originally from South East Asia, it’s been rapidly expanding its range in Europe, and was first seen in the UK in August 2012. Unlike like other Drosophila, which tend to go in for decaying and rotten fruit, D. suzukii uses its serrated ovipositor to lay its eggs through the skins of otherwise undamaged fruit. A neat evolutionary advantage for it, really bad news for growers of soft fruit.

The pest control industry is very much all over trying to get the better of this species, though there is no perfect formula. Research has suggested that using biological methods, in this case entomopathic nematodes and fungi, can reduce population development, but can’t stop outbreaks.

South American tomato moth (Tuta absoluta)

Another great name, another insect to strike fear into growers. Unsurprisingly, it’s massively into tomatoes, and can do enormous damage to crops when left unchecked – to the point when they can finish off the lot. Although numbers of outbreaks in the UK are still relatively small, the potential to penetrate all parts of the tomato plant means that any arrivals, such as in imports of Spanish tomatoes, must be taken very seriously indeed.

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The tomato isn’t looking great either (Photo: TNAU Agritech Portal)

Full development from egg to adult has been seen in a wide range of temperatures, and a 2013 study concluded that Tuta is “well able to develop under temperatures that would commonly be experienced in UK glasshouses”.

Other research has highlighted the potential of natural enemies to counter this tomato-loving moth, with Macrolophus and Nesidiocoris tenuis, two Hemipteran egg predators, now seen as having the best potential to make inroads into populations. The problem with this approach is that sometimes a beneficial insect can become a pest, and in this case, the biocontrols have been known to do plant damage themselves. Nothing is ever completely straightforward in the world of pest management, it seems.

Diamondback moth (Plutella xylostella)

There have been recent spikes in numbers of this lover of cabbage and cauliflowers, sparking natural concern among growers. Evidence is mounting that it’s surviving winter here, as well as resistant to pesticides.1280px-Plutella_xylostella1

The fight is by no means over, however. Intercropping – growing a different crop in proximity to the main one – looks like a promising tactic in taking on the pest. A 2010 study showed that planting onion, tomato or pepper with cabbage was as effective as spraying.

Melon thrips (Thrips palmi)

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Photo: Forestry Images/ Wikimedia Commons

Although this thrips species can’t survive the British winter, it can establish with protected crops, and is extremely unfussy in its choice of meal. As such, it’s as much a threat to growers of ornamental plants as it is to those in the fruit and veg business.

What’s more, it’s another insect known for being highly pesticide resistant, so effective biological controls are certainly what’s called for here. It seems likely that a mix of entomopathic nematodes and fungi may well be the dream team for tackling both the larval and adult stages.

 

Is that it?

Far, far from it. The insects featured here are certainly not the only ones that could potentially do significant harm in UK agriculture, should they both get the chance to arrive and find a way to consolidate their numbers here.

DEFRA’s top six of the very latest potentially damaging pests and diseases features a pair of longhorn beetles from the east, while the UK Plant Health Risk Register is a fascinating and somewhat frightening source of information about potential threats to the flora of this island. Currently listing 1,024 pests (not just insects, however), it serves to highlight that amidst the great advantages to global trade come some pretty serious pitfalls.

The prizes for pests that manage to establish themselves in the UK’s famously un-tropical climes are significant – and in an agricultural environment of reducing pesticide effectiveness and use, controlling their proliferation is a multi-faceted and often complex game.

Successful pest management has to take into account factors like the temperatures insects operate in, where they operate in the crop canopy, the need to tackle both adult and juvenile stages, and compatibility of biological control methods with insecticides and fungicides. It also needs to factor in a comprehensive clean-up after the pest has been beaten, to prevent an immediate repeat of the nightmare all over again.

While there are plenty of checks in place to try and prevent invasive pests getting the chance to test their resolve against the UK climate, it’s practically impossible to prevent every insect of potential harm making it past the border. The prerogative is that when they do show up, they are reported quickly, and expert advice sought when needed. If the last fortnight’s lecturers were anything to go by, there certainly is the expertise out there to nip most comers in the bud before scares become crises.

What’s the point of wasps?

‘But seriously, what is the point of wasps?’ This is a question I often find myself being asked. Unlike their cute, somewhat fluffy cousins, the bees, it seems people have a much harder time accepting wasps. Indeed, they often find themselves on the wrong end of extreme prejudice with people willing to swat them without hesitation; there is even an ‘anti-wasp’ internet meme! This ‘speciesism’ should hardly be surprising given the emphasis placed on pollination services provided by the Apiformes. Wasps however, also play an important role in the functioning of our ecosystems; the health of which we rely upon for our very survival.

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Perhaps the single most important thing that wasps do for us is the provision of ecosystem services though pest control. Many species of social wasp are veracious generalist predators, with each nest capturing and removing many kilograms of arthropod prey from an ecosystem every year (Harris, 1996). Much of this removed biomass is that of species which would otherwise represent significant pests to our agricultural and forestry systems. Wasps can be so efficient at predating on arthropods that in some ecosystems where they have been introduced they actually represent a conservation concern by out-competing native insectivorous birds (Beggs, 2001).

Given this ability to help maintain the functioning of ecosystems, social wasps have occasionally been deliberately employed or encouraged as pest control agents. The introduction of nests has been used to provide successful biological control in production of cotton, tobacco, cabbage, coffee, fruit and timber (Spradbery, 1973). In fact, it is surprising how under-utilised they are considering their apparent ability to effectively control pests. Due to their generalist nature, in many ways social wasps are more highly suited for bio-control than some of some of the specialist species which are currently more widely used. For example, not only will they help maintain populations of multiple pest species below the levels that might affect yield, they are also able to maintain their own populations by utilising various other food sources. This means that their population is not tied to that of the pest species thus there is no ‘lag time’ between the initial outbreak and the time when there are sufficient numbers of predators to have a controlling effect. Furthermore, the social foraging behaviour of wasps causes them to return to sites with abundant food resources, meaning they will concentrate disproportionately at sites with highest pest densities, unlike other biological control agents which tend to distribute themselves more evenly (Richter, 2000). This will allow for more efficient control as the most damage occurs at the sites of greatest pest densities, which will be targeted first by the wasps.

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Contrary to what some people might believe, it is not just bees which pollinate! In fact, any insect which visits flowers has the potential to act as a pollinator. This includes beetles, butterflies, moths, flies and yes, even wasps. In fact, some plants, such as the Chiloglottis orchids, can only be pollinated by a single specific species of wasp (Peakall, 1990). Wasps normally pollinate during their search for carbohydrate rich nectar, but will occasionally frequent flowers during their search for prey. Sometimes they are even tricked into visiting flowers in reaction to volatiles released by the plant! Some species have evolved the ability to produce chemicals to attract male wasps by mimicking female sex pheromones (Schiestl et al., 2003) or by releasing damage signal volatiles to mimic pest damage to attract hunting wasps (Brodmann et al., 2008).

Wasps also have much to teach us. It was by watching wasps create their nests by mulching wood that Cai Lun, an official of the Chinese court of the Han Dynasty, first developed the idea of paper around 105AD. This now ubiquitous technology underlies much of the functioning of our society and owes its inspiration to the remarkable wasps. Even today we are learning much about social evolution by examining the range of socialities exhibited by wasps along with the underlying genomics.

By examination of the services that an organism provides us, it may become easier to justify why we should respect and safeguard them. This carries with it however, the danger that we should only value an organism by what it contributes to ourselves. This narcissistic view is dangerous as in reality human-kind knows very little about the complex world we inhabit. Surely species have a right to exist that is not solely determined by their detectable utility to one other particular species? Even if wasps did not provide us with all of these fantastic services free of charge, I would argue that they are beautiful creatures in their own way. Each individual organism we see around us represents the culmination of millions of years of evolution. Surely it should be a pleasure to share the planet with these creatures. This, I would argue, is ‘the point of wasps’.

By Liam Crowley.

References:

Ballou, H.A., 1913. Report on the prevalence of some pests and diseases in the West Indies during 1912. Barbados, West Indies, Bull. 13, pp.333-357.

Beggs, J., 2001. The ecological consequences of social wasps (Vespula spp.) invading an ecosystem that has an abundant carbohydrate resource. Biological Conservation, 99(1), pp.17-28.

Brodmann, J., Twele, R., Francke, W., Hölzler, G., Zhang, Q.H. and Ayasse, M., 2008. Orchids mimic green-leaf volatiles to attract prey-hunting wasps for pollination. Current Biology, 18(10), pp.740-744.

Harris, R.J., 1996. Frequency of overwintered Vespula germanica (Hymenoptera: Vespidae) colonies in scrubland‐pasture habitat and their impact on prey. New Zealand journal of zoology, 23(1), pp.11-17.

Peakall, R., 1990. Responses of male Zaspilothynnus trilobatus Turner wasps to females and the sexually deceptive orchid it pollinates. Functional Ecology, pp.159-167.

Richter, M.R., 2000. Social wasp (Hymenoptera: Vespidae) foraging behaviour. Annual review of entomology, 45(1), p.142.

Schiestl, F.P., Peakall, R., Mant, J.G., Ibarra, F., Schulz, C., Franke, S. and Francke, W., 2003. The chemistry of sexual deception in an orchid-wasp pollination system. Science, 302(5644), pp.437-438.

Spradbery, J.P., 1973. Wasps. An account of the biology and natural history of social and solitary wasps, with particular reference to those of the British Isles. London: Sidgwick and Jackson Limited, pp.282-283.