Mealybug

Planococcus citri

Mealybug

Planococcus citri

Mealybug

Planococcus citri

Mealybug

Planococcus citri

Marigold Mealybug (Planococcus citri): A Serious Polyphagous Pest

Planococcus citri, commonly known as the citrus or marigold mealybug, is a highly polyphagous and adaptable pest. It thrives under various climatic conditions and can rapidly reproduce, making it a significant threat to numerous crops. This mealybug is notorious for infesting over 200 plant species across 191 genera and 82 families. Though originally from the Old World, it has spread globally through human-mediated transport of infested plant material. Due to its small size and hidden presence on plant surfaces, detection during plant quarantine is difficult. It causes both direct and indirect damage to plants and is also a vector for certain plant viruses like the Cacao swollen shoot virus (CSSV). Below are key points highlighting its characteristics and impact:

Key Points on Planococcus citri (Marigold Mealybug):

1. Host Range and Distribution:

   • Extremely polyphagous; reported on over 200 host species from 191 genera and 82 families (García et al., 2016).

   • Widely distributed in temperate and tropical regions; survives under greenhouse conditions in colder areas.

2. Feeding Behavior and Plant Damage:

   • Feeds by sucking sap from various plant parts, leading to wilting and stunted growth.

   • On cocoa, attacks flower stalks, buds, and young pods (Entwistle, 1972).

   • In Taiwan, causes deformation and premature drop of immature coffee berries (Moriyama, 1941).

3. Indirect Damage via Honeydew and Sooty Mould:

   • Excretes sugary honeydew that fosters growth of sooty moulds (Gausman and Hart, 1974).

   • Mould covers leaves, hindering photosynthesis and reducing plant vitality.

4. Virus Transmission:

   • Second most important vector of several strains of Cacao swollen shoot virus.

   • Virus symptoms include leaf chlorosis, root necrosis, stem swellings, and dieback (Posnette, 1941; Cotterell, 1943).

5. Reproductive Biology:

   • Reproduces sexually; egg-laying starts 9–14 days post-fertilization.

   • Females lay 150–500 amber-yellow eggs in a waxy ovisac depending on host and conditions (Côte d'Ivoire, Ghana, Trinidad, California).

6. Developmental Stages:

   • Female mealybugs pass through three nymphal instars before reaching adulthood.

   • Nymphs are more mobile and have a thinner wax coating than adults.

7. Male Development:

   • Males resemble females in early instars but later undergo non-feeding prepupal and pupal stages.

   • Though early reports suggested rarity of males (Betrem, 1936), other studies show a near-equal sex ratio (James, 1937; Myres, 1932; Padi, 1997b).

8. Temperature and Development:

   • Development influenced by food quality and temperature (Arai, 1996).

   • Lower developmental threshold: 7.7°C (nymphal stage), 8.0°C (pre-ovipositional).

   • Thermal constants: 401 DD (nymphal), 378 DD (pre-ovipositional).

9. Challenges in Control and Spread:

   • Cryptic nature and small size hinder detection during plant inspections.

   • Global trade in fresh plant material continues to aid its spread.