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.
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.
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).
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.
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.
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.
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!