Diomus

Mulsant, 1850

lady beetles, ladybirds

Species Guides

9

Diomus is a of small lady beetles (Coccinellidae) comprising at least 20 described . Species within this genus exhibit diverse ecological strategies, including on mealybugs and aphids, as well as specialized myrmecophilous associations. Several species have been evaluated or employed as agents against agricultural pests such as the papaya mealybug (Paracoccus marginatus), yellow sugarcane aphid (Sipha flava), and cassava mealybug (Phenacoccus manihoti). The genus shows notable variation in associations, from agricultural crops to nests.

Diomus amabilis by (c) Justin Williams, some rights reserved (CC BY), uploaded by Justin Williams. Used under a CC-BY license.Diomus by (c) Donald Hobern, some rights reserved (CC BY). Used under a CC-BY license.Diomus by (c) Donald Hobern, some rights reserved (CC BY). Used under a CC-BY license.

Pronunciation

How to pronounce Diomus: /ˈdai.ɔ.mus/

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Identification

Diomus are generally small coccinellids, with Diomus terminatus measuring 1.9–2.1 mm. in coloration has been documented in some species: D. terminatus males have black and pronota with yellowish-brown , while females have reddish-brown heads and pronota with darker brown elytra. Larvae are typically dark gray to black with distinctive orange lateral markings. Precise identification to species level requires examination of male genitalia and detailed morphological characters.

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Habitat

vary by and include agricultural crops (sugarcane, citrus, papaya, cassava), forage grasses, ornamental plants, and nests. Diomus thoracicus larvae are exclusively found in nests of the ant Wasmannia auropunctata. Agricultural associations often involve of mealybugs or aphids on plants.

Distribution

The has a broad geographic distribution spanning Africa (native range of D. guilavoguii in Guinea), South America (D. thoracicus in French Guiana), North America (D. terminatus in Florida and Louisiana, USA), Australia (D. flavifrons, D. notescens), and Asia (D. guilavoguii established in Guangdong Province, China). Specific distributions vary by .

Diet

Predominantly predatory on Hemiptera. Documented prey includes mealybugs (Pseudococcidae: Paracoccus marginatus, Phenacoccus manihoti, Planococcus citri) and aphids (Aphididae: Sipha flava, Melanaphis sacchari, Aphis gossypii). Diomus thoracicus larvae are myrmecophagous, feeding exclusively on (Wasmannia auropunctata).

Host Associations

Life Cycle

Complete with four larval instars. Development rates vary by and temperature. Diomus terminatus: (2.3 days), four larval instars (3.9, 1.4, 1.4, 2.4 days), pupa (3.1 days), total 16.5 days at 25°C. Diomus guilavoguii: four larval instars described, pupal stage present. Diomus flavifrons: egg to 23.7 days at 27°C. Diomus seminulus: development slower at lower temperatures, eggs non-viable at temperature extremes (16°C and 28°C).

Behavior

and larvae are active that aggregate in prey colonies. Some use (mealybug wax and honeydew) to locate prey; experienced individuals may show prey-specific preferences. Diomus thoracicus larvae exhibit obligate myrmecophily, living in nests through chemical mimicry of cuticular cues. occurs in D. terminatus when prey is scarce. Adults of some species are long-lived with extended oviposition periods.

Ecological Role

Natural enemy of mealybugs and aphids in agricultural and natural . Several function as agents, with documented rates: D. terminatus fourth instar larvae consume ~65 aphids/day, ~52/day; D. guilavoguii established in China contributes to suppression of papaya mealybug. Diomus thoracicus represents a specific of the invasive Wasmannia auropunctata.

Human Relevance

Significant value in of agricultural pests. Diomus have been introduced across continents for pest management: D. guilavoguii from Africa to China, Diomus sp. from South America to Africa for cassava mealybug control. Evaluated for control of yellow sugarcane aphid in Brazil (D. seminulus) and USA (D. terminatus). Potential for in citrus, sugarcane, and papaya production systems.

Similar Taxa

  • ExochomusBoth are coccinellid of mealybugs; Exochomus is African-native and shares -mediated prey-finding with Diomus, though Exochomus is generally larger and lacks the myrmecophilous specialization seen in some Diomus .
  • Cryptolaemus montrouzieriBoth are small coccinellids used for mealybug ; Cryptolaemus larvae have distinctive waxy filaments resembling mealybugs, while Diomus larvae lack such filaments and have dark coloration with orange markings.

More Details

Chemical ecology

Diomus respond to from mealybugs, including wax and honeydew. Experienced D. guilavoguii show preference for kairomones of their rearing prey (cassava mealybug) over alternative mealybug species. Diomus thoracicus larvae achieve integration into nests through chemical mimicry of cuticular hydrocarbons.

Temperature sensitivity

Development and in Diomus seminulus are strongly temperature-dependent, with viability reduced at 16°C and 28°C, suggesting narrow thermal optima may limit establishment in some environments.

Taxonomic uncertainty

The status of D. guilavoguii relative to D. hennessyi has been discussed in recent literature, indicating potential taxonomic revisions within the .

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