Polydrusus formosus

Last update: 26 September 2020
SPECIES: Polydrusus formosus
GENUS: POLYDRUSUS
FAMILY: Snout beetles (CURCULIONIDAE)



OBSERVATION:
2016-V-28

YEARS:
2016

MONTHS:
JanFebMarAprMayJunJulAugSepOctNovDec


This nice shiny green beetle is Polydrusus formosus from the family of Snout beetles, or Weevils (Curculionidae) [1, 2].

Some publication use its older scientific names [5]:

  • Polydrusus splendidus (Herbst, 1784)
  • Polydrusus sericeus (Schaller, 1783)
Polydrusus formosus
Polydrusus formosus
Polydrusus formosus

CONTENTS

1. Distribution
2. Behaviour
3. Plant relations
4. Prey relations
5. Identification

1. DISTRIBUTION

Pformosus is a common beetle in the Netherlands and in the garden.

It prefers wooded borders, parkland, gardens and wastelands, anywhere as long as its host plants are there [6].

2. BEHAVIOUR

2.1. ACTIVITY

Active from April to August [3].

The adult animals browse theleaf and flower butts, young leafs and blossoms.

2.2. DEVELOPMENT

Adults lay their eggs single or in small clusters [6], in the bark or on the leafs of the host plant [3]. The larvae live in the ground and feed on the plant roots [3,6]. In autumn their development is complete and they overwinter as puppa in the ground [6] and hatch in spring [3].

2.3. DEFENSE MECHANISMS

When the beetle feels threatened it will drop and pretend to be dead.

Polydrusus formosus

3. PLANT RELATIONS

The beetle uses a number of host plants [3,6,8,9]:

PlantPresents
Maple (Acer)
Alder (Alnus)vicinity
Birch (Betula)vicinity
Hazel (Corylus)garden
Hawthorn (Crataegus)
Apple (Malus)garden
Poplar (Populus)vicinity
Prunus
Pear (Pyrus)
Oak (Quercus) vicinity
Willow (Salix)
Elm (Ulmus)

The species has a large preference for Birch (Betula) [8,9], which increases fecundity substantially [8,9]. In lab circumstances this resulted in females with access to Birch would lay an average of 29 egg a day, whereas the females that were feeding on Maple laid only 2 eggs a day on average [8].

Adults are known to cause damage on fruit butts, shoots and blossoms in fruit trees but do not become a pest. At least on apple, the damage can result in cork-like scars [4].

4. PREY RELATIONS

The species is hunted by the following predators:

Diggerwasps
(HYMENOPTERA, Crabronidae)

GenusSoort
Cerceris [4]Cerceris arenaria [10]

In de tuin zijn de volgende rovers geobserveerd:

FamilyGenus / Species
Diggerwasps
(HYMENOPTERA, Crabronidae)
Cerceris
Cerceris arenaria

5. IDENTIFICATION

A number of similar looking beetles reside in the Netherlands, which can make determination difficult [5].

5.1. EGGS

Freshly deposited eggs are bright yellow in color and gradually fade to white [8].

They are ±0,5×0,3 mm in size [8].

5.2. LARVAE

Larvae are about 7 mm in length, are C-formed with a cream-white color with brown head [4].

5.3. ADULTS

Adults are 5 to 8 mm [4, 7] in length.

The next characteristics are keys to identification [1]:

Female + Male

  1. Eyes located to side of head
  1. Neck shield edge without hairs
  2. Neck shield edge straight, doesn’t cover eyes
  3. Shoulders clearly wider than neck shield and rounded corners
  4. Antennae implanted near side of the snout
  5. Antennae don’t extend over back edge eye when it would lie flat to the side of the head
  6. Antennae segments III to VII much longer than wide
  7. Area between eyes narrower than area between antennae holes
  8. Black body entirely covered in dense and evenly spread metallic green round scales (the scales can wear revealing black spots or entire black area’s)
  9. Antennae and legs red-yellow to red
  10. Legs with barely visible teeth
  11. Antennae holes on snout black
  12. Large eyes that barely protrude
  13. Elytra (wing covers) near tip normally develope and tightly adjoined
  14. Snout tip weakly widened

Male

  1. Backside hindshins with long hairs
Eyes large and weakly protuding, antennae holes near on side head
Body covered in metallic scales, elytra close near seamlessly at apex
Space between antennae holes wider than space between eyes
Antennae flagellum segments III – VII much longer than wide

Males in this species can be identified based on the following characteristics [7]:

  1. richel op het laatste sterniet apex (segment onderzijde)
  2. Groepje lange haren op onderhelft achterzijde achterscheen

As I couldn’t find any comparison material and the photo evidence quality is not that great I’m not 100% sure, but it could be a male.

Male? Long hairs on the lower half of the backside of the hindshins, last abdominal sternite emarginate apically

References

1 Die Käfer Europas, Ein Bestimmungswerk im Internet, Herausgegeben von Arved Lompe, Nienburg/Weser, Begründet im September 2002

2 Kerbtier.de Käferfauna Deutschlands

3 NatureSpot - Recording the Wildlife of Leicester & Rutland

4 Alford, D. (2014). Pests of Fruit Crops. Boca Raton: CRC Press, https://doi.org/10.1201/b17030

5 Nederlands Soortenregister

6 UK Beetles

7 SLEEPER, Elbert L. Notes on North American Species of Polydrusus Germar (Coleoptera: Curculionidae, Brachyderinae): 17. A Contribution to the Knowledge of the Curculionoidea. 1957.

8 PINSKI, R. A.; MATTSON, W. J.; RAFFA, K. F. Host breadth and ovipositional behavior of adult Polydrusus sericeus and Phyllobius oblongus (Coleoptera: Curculionidae), nonindigenous inhabitants of northern hardwood forests. Environmental entomology, 2005, 34.1: 148-157.

9 HILLSTROM, Michael L., et al. Performance of the invasive weevil Polydrusus sericeus is influenced by atmospheric CO2 and host species. Agricultural and Forest Entomology, 2010, 12.3: 285-292.

10 Dr. Guido Bohne, 2014, iNaturalist: observation predator relation Cerceris arenaria ➧ Polydrusus formosus

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