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.

Does Mother Always Know Best? – An Aphid’s Perspective

 

We all remember those teenage years, mum shouting from the doorway to get up and go to school, giving her tit bits of advice and usually finishing a sentence with ‘Don’t argue, I know what’s best for you!’ But what about insects, I’ve never read a study where they try to get their young out of bed early: so, do they know best?

If an insect could talk, would they say ‘thanks mum’? Probably not, more likely ‘who are you’ and have to go onto the Jeremy Kyle show to be told ‘You ARE the mother!’ So, what should a good reporter do? You guessed it, an interview. After hours of searching (okay, ten minutes – I couldn’t find my shoes), an aphid was found (a small pear shaped true bug with sucking mouthparts) 7 and she was not impressed with what I had to say!

After staring hard at her proboscis (wow, suddenly my nose seems very inadequate) we launched into it:

“Can you explain why you are a good mother?”

She huffed. “Honestly have you never read Craig and Ohgushi,2 well, it’s called the naïve adaptatonist hypothesis (something in the way she said naïve makes me think she was directing that right at me, seriously, I’m getting sass off a bug). She continued “It explains that mothers will pick the best site for oviposition (turns out this meant egg laying, I didn’t want to admit it at the time that she had a better vocabulary than me) and by having this plant preference the young laid on these sites have the best survival rates to adulthood.”3 She added breezily “There’s been loads of studies on it.”

“…I mean its easier when we eat the same food as our young, you eat until you want to lay and then just find a good place to do it, perfect. But some of my friends don’t stay here the full year round. They like to travel and have two host plants.3 My friend Mary spends the summer in a tree but each year she pops back to shrubs when she lays eggs to overwinter.”

I sit and think. So are they truly good parents, more importantly, are they better than us?

She continued – “There’s no swanky hospital for us insects, I have to make decisions, I mean, obviously one plant is going to be more nutritious, but what happens if there’s another plant that offers better protection from predators?!”1

“So what happens if you pick the wrong plant” I enquired, I mean how bad could it be?

“Slow growth mostly…”

“Well, that doesn’t sound so…”

“… OR death, from predators or we might not be able to feed from the right leaves.”

I’m feeling guilty; death seems a bit much for just laying your egg in the wrong place. But I’m a reporter and time to play my trump card.

“I’ve heard you just lay your eggs in places which are only beneficial to you.”6

“Where’d you hear that?” she replied.

I shrugged “It’s just a theory.”

“What about the theory that states we lay young elsewhere in order to increase their lifespan?”

Touché! I had to admit I had looked, there are lots of studies out there with conflicting evidence! Some argue larval survival is connected to the mother’s oviposition choice, 5 others have found a weak or no effect.3 How are you suppose to make sense of all this?

“Have you read the latest meta-analysis?”

“Meta-what-now?”

“Analysis, it’s a study which analyses the significance all written studies to see an overall effect, it’s fantastic, explains what I’ve been saying all along, we pick a site that best helps our young.”4

“What about the experiments that don’t work then?” Surely she couldn’t have an answer for everything!

She sighed. “Maybe when it didn’t work it was the research that had problems such as bad weather (though you should already be used to that), wrong plants so you had to make the best of a bad situation, too few insects involved or maybe these lab experiments are not as representative of the wild as you seem to think.”8

Well didn’t this just take a complex turn, I thought I had it all figured out. I don’t think I could make all these right choices, some days I can’t even find two socks that match.

“Nothing’s ever that simple, much to learn you still have, young writer” (wait, did she just quote star wars at me?) and then she was gone.

Turns out I’ve learnt lots, mums like to huff; they like to be right and as it turns out, they usually are, (but don’t tell mine that). So next time your mother gives you some advice, maybe you should listen to her; after all, mother knows best!

By Christina Faulder

References

  1. Björkman, C., Larsson, S. and Bommarco, R. 1997. Oviposition preferences in pine sawflies: a trade-off between larval growth and defence against natural enemies. Oikos, 79 (1), pp.45–52.
  2. Craig, T.P. and Ohgushi, T. 2002. Preference and performance are correlated in the spittlebug Aphrophora pectoralis on four species of willow. Ecological Entomology, 27 (5), pp.529-540.
  3. Friberg, M. and Wiklund, C. 2009. Host plant preference and performance of the sibling species of butterflies Leptidea sinapis and Leptidea Reali: a test of the trade-off hypothesis for food specialisation. Oecologia, 159 (1), pp.127-137.
  4. Gripenberg, S., Mayhew, P.J., Parnell, M. and Roslin, T. 2010. A meta-analysis of preference–performance relationships in phytophagous insects. Ecology Letters, 13 (3), pp.383-393.
  5. Ishiwara, M. and Ohgushi, T. 2008. Enemy-free space? Host preference and larval performance of a willow leaf beetle. Population Ecology, 50 (1), pp.35-43.
  6. Jervis, M.A., Ellers, J. and Harvey, J.A. 2008. Resource acquisition, allocation, and utilization in parasitoid reproductive strategies. Annual Review of Entomology, 53, pp. 361-385.
  7. Kindlmann, P. and Dixon, A.F.G. 2010. Modelling population dynamics of aphids and their natural enemies. In: Kindlmann, P., Dixon, A.F.G and Michaud, J.P. In. Aphid biodiversity under environmental change: patterns and processes. London: Springer Science & Business Media. pp.1-20.
  8. Mayhew, P.J. 2001. Herbivore host choice and optimal bad motherhood. Trends in Ecology & Evolution, 16 (4), pp.165-167.