Controlling Scale Insects with the Ladybird Cryptolaemus montrouzieri
Cryptolaemus montrouzieri is an effective biocontrol agent in the fight against mealybugs. Indeed, both the larva and adult of this predator feed on all developmental stages of mealybugs.
Context
Mealybugs cause significant economic losses, mainly due to a decrease in fruit marketability caused by the massive development of sooty mold on the honeydew excreted by the mealybug, which accumulates on leaves and fruits. For example, in several infested orchards in southern France, up to 80% of harvested fruits are discarded when infestation levels are high and the accumulation of black mold is particularly severe on the surface or carpel of the fruits[1].
Biocontrol as an alternative strategy to chemical products against mealybugs
Control of mealybugs using conventional insecticides is difficult because mealybugs are covered with a waxy substance and due to their cryptic nature. The development of insecticide resistance is a serious problem in both tropical and temperate climates. Due to increasing awareness of the dangers of insecticides regarding soil, water, and atmospheric pollution, biological control approaches seem to be the safest and most accessible way to manage mealybugs. Managing these pests using a biological control strategy is advantageous because biocontrol agents are persistent and sustainable in the environment after release and have a low cost[2].
Introduction of the biocontrol agent Cryptolaemus montrouzieri
Cryptolaemus montrouzieri is a beetle predator of mealybugs. It is an effective biocontrol agent against these pests, as both the adult and larval stages have a voracious appetite for the different developmental stages of the mealybug. It has also been commercialized and widely used in more than 40 countries, especially in greenhouses and on perennial crops[2]. It is also known as the "mealybug destroyer".
Mode of action and effectiveness
Cryptolaemus montrouzieri can reproduce by feeding solely on mealybugs. It has been observed that all stages of the predator feed on all stages of the mealybug life cycle, including eggs, larvae, and adults. Eggs are laid on the cottony egg masses of mealybugs, larvae can feed on mealybugs for 12 to 17 days, then pupate. A single larva can consume up to 250 small mealybugs[3].
The feeding potential of Cryptolaemus montrouzieri increases significantly as its developmental stages progress, ensuring a continuous predation rate over time.
Spectrum of action
C. montrouzieri has evolved as a predator feeding mainly on phytophagous hemipterans. It poses no risk of attacking crops or natural vegetation. C. montrouzieri is adapted to feed on small prey species, that are slow-moving and soft-bodied, such as mealybugs.
The table below shows the prey of Cryptolaemus montrouzieri (Coleoptera : Coccinellidae), according to the Plant-SyNZ database (July 15, 2017). The reliability index indicates the effectiveness of the association with the prey (++++ = high effectiveness) [1], which guarantees the survival of C. montrouzieri.
| Scientific name | Common name | Reliability index |
| Bactericera cockerelli | Potato psyllid | ++ |
| Balanococcus diminutus | Flax mealybug | ++++ |
| Coccus hesperidum | Hesperid scale | ++++ |
| Coelostomidia zealandica | Giant mealybug | ++ |
| Dysmicoccus ambiguus | +++ | |
| Eriococcus araucariae | Pine felt scale | ++++ |
| Eriococcus pallidus | Karo felt scale | ++++ |
| Nipaecoccus aurilanatus | Golden mealybug | ++++ |
| Paracoccus glaucus | Long egg mealybug | ++++ |
| Paraferrisia podocarpi | Kahikatea mealybug | ++++ |
| Parasaissetia nigra | Black scale | +++ |
| Pseudococcus calceolariae | Citrophilus mealybug | ++++ |
| Pseudococcus longispinus | Long-tailed mealybug | ++++ |
| Pulvinaria mesembryanthemi | Ice plant scale | ++++ |
| Saissetia oleae | Black scale of olive | ++++ |
Survival is high to moderate when the predator is placed in an area containing prey closely related to mealybugs. However, a reduction in predator fitness has been observed when offered prey species that are not mealybugs.
Instructions for use
For best results
The optimal conditions for using Cryptolaemus montrouzieri are 28°C with a relative humidity of 70 to 80%, but it can be used between 16 and 33°C. The predator is completely inactive below 9°C, while above 33°C it stops searching for prey. It is therefore recommended to release it early in the morning or late in the evening, as light and bright colors repel it away from plants. It is also important to use the predator between affected leaves or on the stem [2].
The predator tends to disperse when released. In greenhouses, windows and vents should be closed on the day of release.
Introduction rate
The dose of Cryptolaemus montrouzieri depends on the climate, crop, and mealybug density and must always be adapted to each situation. It may also depend on attack history and the purpose of the introduction.
- Outdoors : 1250-12500 beetles per hectare, near the mealybug population. The first release should take place in early spring.
- Orchards : 2500-5000 beetles per hectare.
Many deciduous trees grow slowly, so it may be necessary to wait 2 to 4 months before seeing results from biological control programs against mealybugs. New uninfested growth is a sign of control [3].
After release
Regular monitoring by an expert is recommended after release to verify that Cryptolaemus has established, as predator larvae resemble mealybug larvae.
Repeated applications may be necessary for heavy infestations. Repeat releases every 2 weeks until clear observation of established predator populations on the plant.
Cultural practices to facilitate establishment
Adult C. montrouzieri have a strong flying ability and establish widely if a large mealybug population is present or if special effort is made to keep predators near the infestation site.
- For outdoor situations, installing net cages at strategic locations can greatly improve the establishment of the mealybug destroyer.
- In greenhouses, an effective technique is to confine part of the C. montrouzieri population on heavily infested plants using a mosquito net or similar material for a few days while they lay eggs, to facilitate pupation and protect them from bright lights that could distract them from the release area [4].
Cryptolaemus Montrouzieri and pesticide use
After releasing C.montrouzieri, avoid using insecticides based on carbamate, organophosphate, and synthetic pyrethroid.
It is recommended to release the mealybug predator at least 4 weeks after applying these pesticides. Insect growth regulators can be harmful to the biocontrol agent. Sprays of nutrients and copper are considered safe, and many acaricides are also harmless. Avoid using insecticidal oils or soaps, as they can harm C. montrouzieri. However, residues of these products on leaves are considered non-toxic [5].
Ant control
Ants must be controlled because they defend mealybugs against the predator to protect their honeydew.
There are different methods to control ants [6], for example :
- Use of hot water at 47°C to kill ants in their nests. However, hot water up to 49°C does not damage the crop.
- Use of "Tanglefoot", a tape coated with a sticky inert substance made from natural ingredients such as vegetable oil, tree resins, and others. This product should be wrapped around the tree trunk and replaced when it becomes full of dead ants or debris.
- Remove all low branches that allow ants to reach mealybugs on trees.
- Use of baits for ants and disruption of their mounds.
Storage
It is recommended to release Cryptolaemus montrouzieri as soon as possible after the product containing the predator arrives. If necessary, beetles can be stored for up to 2 days in darkness at about 17°C and fed with honey [7].
Relative cost
Using Cryptolaemus montrouzieri as a biocontrol agent against mealybugs has a cost (see table below), prices depend on several parameters (see section Introduction rate).
| Conditions | Introduction rate
per hectare |
Cost
per hectare [8] |
| Outdoors | 1250-12500 | 615 - 6150 euros |
| Orchard | 2500-5000 | 1230 – 2460 euros |
References
- ↑ Kreiter, P., & Germain, J.-F. (2005). Pseudococcus comstocki, a new species for France and Aonidiella citrina, new for Corsica (Hem., Pseudococcidae and Diaspididae). Bulletin de la Société Entomologique de France, 110(2), 132.
- ↑ 2.0 2.1 Gunawardana, D. U. M., & Hemachandra, K. S. (2020). Mass Rearing of Mealybug Predator, Cryptolaemus montrouzieri Mulsant (Coleoptera : Coccinellidae) on two Mealybug Species, Planococcus minor and Pseudococcus viburni. Tropical Agricultural Research, 31(1), 31. https://doi.org/10.4038/tar.v31i1.8342
- ↑ Kaur, H., & Virk, J. S. (2012). Feeding potential of Cryptolaemus montrouzieri against the mealybug Phenacoccus solenopsis. Phytoparasitica, 40(2), 131‑136. https://doi.org/10.1007/s12600-011-0211-3
