Cladius

Taxonomy

Family: Tenthredinidae
Family common name: common sawflies
Subfamily: Nematinae
Tribe: Cladiini
Genus: Cladius Illiger, 1807
Subgenera: Cladius, Priophorus, Trichiocampus

Background

The Tenthredinidae are the most species-rich family and are found throughout the world, in all continents but Antarctica. They are known as the “common sawflies.” They can generally be recognized by a cylindrical body and long, segmented antennae. Otherwise, they come in a variety of colors, sizes, and forms (Goulet 1992).

Nematinae is the second-largest subfamily of Tenthredinidae, with over 1,250 species (Prous et al. 2014). They are most diverse in northern Eurasia and North America; only a few species occur in the Southern Hemisphere. Nematinae sawflies have a variety of feeding habits including external leaf feeding, leaf mining, and gall forming, and feed on a variety of hosts (Smith 2003b).

The Nematinae have been subject to numerous revisions in recent years. As of 2021, there are no comprehensive keys to many of the North American species of Nematinae (Prous et al. 2014). Because of changing taxonomy and extreme variability in morphology, identifying genera and species in the Nematinae may be more challenging than in other subfamilies of Tenthredindae. For this reason, knowing the host or behaviors of a specimen can be extremely helpful for identification within this subfamily.

Cladius are generally entirely black, small, and inconspicuous (Rohwer and Middleton 1922). Larvae, however, are distinctly hairy, and many are common pests in North America (Smith 1974b). The taxonomy of the genus Cladius is the subject of some debate, with many authors treating current subgenera Cladius, Priophorus, and Trichiocampus as separate genera (Vikberg 2013).

Diversity

There are 46 described species worldwide. Eight species occur in North America (Taeger et al. 2018).

A key to North American species (as Cladius, Priophorus and Trichiocampus) is included in Smith 1974b.

Diagnostic characteristics

Subfamily characters​

Genus characters

May be confused with

Cladius may be confused with other genera in the subfamily Nematinae — especially those that include several entirely black species such as Pristiphora — but can be distinguished from most others by the closely spaced fore wing veins M and Rs+M on vein R. Cladius difformis males are easily recognized by pectinate antennae (Goulet 1992).

Exotic pest species of concern

The hemp sawfly, Cladius cannabis, is a pest on cultivated Cannabis sativa in China and has recently spread into western Russia. The larvae feed heavily on the foliage and skeletonize leaves. The species is bivoltine in its known range, and can reproduce without the presence of males (Vikberg 2013).

Cladius brullei (as Priophorus morio) was introduced to Hawaii as a biocontrol agent to control wild blackberry (Davis and Krauss 1967, Davis and Chong 1969, Smith 1974b). Conversely, it was accidently introduced to New Zealand and Australia and is a damaging pest of raspberries there (Callan 1978). It has also been introduced into South America (Lucía et al. 2007).

Native or introduced pest species

Cladius difformis, also known as the bristly rose slug, is a pest of roses cited as the “most common defoliator of roses in the eastern states” (Rohwer and Middleton 1922). Females oviposit in rows into the petiole of a leaf. The larvae, which are distinctively hairy, feed on the leaf tissue, leaving holes and blotches, eventually skeletonizing the leaf. At maturity, the larvae spin thin, papery cocoons to pupate or overwinter. In the summer, the life cycle only takes about 30 days to complete, and the species can complete 4–6 generations per year, so the damage from repeated feeding can be severe (Smith 1974b).

Cladius grandis, known as the poplar sawfly, is a pest on several species of Populus. It is known to defoliate entire trees when larvae are present in high abundance. Interestingly, larvae will search for pupation or overwintering locations and will sometimes end up inside homes and buildings. One record in Victoria, British Columbia claims thousands of larvae were climbing the walls of a house behind a poplar grove and had to be removed “by the shovelful” (Downes 1925).

Host associations

In North America, Cladius feeds on species of Rosa (rose), Betula (birch), Salix (willow), Rubus (blackberry), Alnus (alder), Crataegus (hawthorn), Prunus (cherry/plum), and Populus (poplar/cottonwood) (Smith 1974b).

Life history

Females oviposit into leaves or leaf petioles in short rows. Larvae feed externally, then pupate or overwinter in the soil. All studied species are multivoltine (Smith 1974b).

Larvae of Cladius are generally hairy and are capable of producing glandular secretions for chemical defense (Boevé et al. 2000). Species in the subgenera Cladius and Priophorus are cryptically colored and solitary, while those in the subgenus Trichiocampus are brightly colored, gregarious, and unpalatable to birds — a combination of larval traits which likely represents a suite of defensive mechanisms against predators (Boevé et al. 2000).

Distribution

World: The genus is known from North America, throughout Europe, Turkey, Iran, China, and Vietnam (Wei 2000, Khosravi et al. 2014, Kato and Shinohara 2018). Cladius brullei was introduced to New Zealand in 1936 and Australia in 1959, where it is now established (Callan 1978), and to Chile in 2002 and Argentina in 2007, where the status is not known (Lucía et al. 2007).

North America: Cladius occurs through the northern United States and Canada, as far north as Alaska and Yukon (Smith 1974b, GBIF). Cladius difformis is recorded as adventive in Hawaii, but may not be established as no new collections have been made since 1976 (Nakahara 1979, Janis Matsunaga pers. comm.). Cladius brullei was introduced to Hawaii in 1966 and 1968 and is now established on Hawaii Island (Davis and Krauss 1967, Davis and Chong 1969, Janis Matsunaga pers. comm.).

Map data from: GBIF.org (29 October 2019) GBIF Occurrence Download Cladius

Details about data used for maps can be found here.

Cladius pectinicornis female lateral habitus; photo by J. Orr, WSDA

Cladius pectinicornis female lateral habitus; photo by J. Orr, WSDA

Cladius pectinicornis female dorsal habitus; photo by J. Orr, WSDA

Cladius pectinicornis female dorsal habitus; photo by J. Orr, WSDA

Cladius pectinicornis female face; photo by Q. Baine, WSDA

Cladius pectinicornis female face; photo by Q. Baine, WSDA

Cladius pectinicornis male lateral habitus; photo by J. Orr, WSDA

Cladius pectinicornis male lateral habitus; photo by J. Orr, WSDA

Cladius pectinicornis male dorsal habitus; photo by J. Orr, WSDA

Cladius pectinicornis male dorsal habitus; photo by J. Orr, WSDA

Cladius pectinicornis fore wing; photo by P. Jones, WSDA

Cladius pectinicornis fore wing; photo by P. Jones, WSDA