Mealybug plague

December 10th, 2005

wolluis4.jpgThis summer we had our first mealybug plague. We found the mealybug at 3 large plants. We took those plants out of our greenhouse, 2 heleconia’s which we pruned till 10 cm, the mealybugs loved especially the many flowers and the leaves. In the meantime the heleconia’s recovered quite well, grow fast and have flowers again. We still have them in our closed veranda, in case the mealybug returns. The paradisebirdplant we also still keep in our closed veranda, we had to clean its strong leaves several times with a wet sponge, but it looks good now.
But last month we had all of a sudden a real mealybug explosion. Within a week about 10 plants where completely covered with mealybugs. All plants were located around the spot where the largest heleconia with the most mealybugs had stood. wolluis7.jpgProbably a small center of infection remained there from this summer. Also a few other plants spread over the greenhouse had some mealybugs. We vacated the mealybugcenter, even the sand and peatblocks and the few plants with little mealybugs. But last week another plant was covered again with mealybugs and one plant had a few mealybugs. We called Entocare, a company in biological crop protection, we could send them some leaves with mealybug so they could determine what kind of variant it was to send us the right variant of parasitic wasp. This beside the mealybugdestroyer, the cryptolaemus montrouzieri beetle. It appeared we had the longtailed mealybug. They advised us the larvae of the beetle, they eat up to 30 mealybugs a day. After about 3 weeks the larvae will be adult, then they have eaten themselves quite full and can reproduces themselves better. Egg to adult development takes wolluis2.jpgabout 30 days at a temperature of 25°C. During her lifespan a female can lay up to 400 eggs. The eggs are deposited within the egg masses of the mealybugs. Larvae will eat each other whenever food availability is poor. This beetle can be very effective in cleaning hot spots of infestations. Adult beetles are 3-4 mm in size.
We first caught as many spiders as we could find and removed their webs, as we hope the larvae, beetles and wasps will not get caught that easily in spiderwebs and will be eaten, as before.
We ordered 50 larvae. Biological crop protection is not cheap, 25 larvae costs € 11,00 and 25 parasitic wasps € 20,00. Beside the beetles we ordered a mixed portion of 25 parasitic wasps. The Anagyrus fusciventris and Leptomastidea abnormis, wolluis5.jpgthe size of the first one is 3mm, the 2nd one is only 1-1½ mm. The first one parasitizes mainly in the later instars of the mealybug, the 2nd one in the first and second instars. One egg is laid per mealybug, The mealybus are killed by the larva of the wasp, who grows op from egg to adult inside the mealybug. At 25ºC this development takes about 15-17 days. The first wasp can live up to 2 months, the 2nd one up to 1 month. A female lays 40-50 eggs a week. Most of them are laid in the first and second week of the female's live. They feed themselves by piercing mealybugs and sucking body fluids from them (host-feeding).
As we put the larvae at the infected spots, they attacked straight away the mealybugs, just gorged and gorged as they had not eaten for weeks. The wasps flew a bit around, but these are so small, you hardly can see them, they are much smaller than the small fruitfly. Hopefully the beetles and wasps exceed in reducing our mealybugplague. It is hard to get the greenhouse completely mealybugfree, but to keep it under control at this way, must be possible.