Symphyta: the First Hymenoptera

So far I have mainly discussed the social insects in the suborder Apocrita (wasps, ants and bees) from which most of Hymenoptera belong to. But there is another suborder of the Hymenoptera – the Symphyta - which contains the sawflies, horntails and parasitic wood wasps. 

Image 1: Paperbark or Melaleuca Sawfly (Lophyrotoma zonalis)

The Symphyta are believed to be the most primitive of the order based on their morphology and being that they are the first hymenopterans found in fossils – the earliest being Xyelidae found in Middle Triassic fossil records from Central Asia (Wang et al, 2014). The Xyelidae are considered to be the basal group from which all other hymenopterans evolved and some of the members of this superfamily have primitive features that have been abandoned by other hymenoptera (Gauld & Bolton, 1988). 

Image 2: Dorsal view of Sawfly (Cathayxyela extensa sp.) fossil found in China (Wang et al, 2014). 

One of the distinctions between Symphyta and Apocrita is the ovipositor – on Symphyta it is saw-like (hence the name sawflies) which allows the female to make slits or borings in the host plant in which to lay her eggs (Gauld & Bolton, 1988). Morphologically the Symphyta also lack the tapered typical wasp-waist and a stinger as seen on the Apocrita and hold their wings flat over the body (The University of Edinburgh, 2001). Although not social, there is evidence of group pupation and some mother Symphyta will provide defence to young and will viciously attack predators (Costa, 2007). 

Image 3: Sawfly (Perga sp.) mother defends her offspring, photo courtesy of Kristi Ellingsen. 

The larvae of Symphyta feed on host plants completely exposed, in leaf rolls/webs or concealed within parts of the plant such as the fruit; however there are some species (from the Orussidae superfamily) that are parasitic (Gauld & Bolton, 1988). Adult sawflies feed from flowers, on parts of the flower and some species are carnivorous (Gauld & Bolton, 1988). The majority of Symphyta larva are caterpillar-like but have at least six pairs of prolegs compared to the caterpillars maximum of five and lack the hooks that caterpillars have on their prolegs (Barnard, 2011). 

Having a similar life to the caterpillar, Symphyta larvae are subject to similar selective pressures as butterfly larva and they have developed similar chemical and communicative defence mechanisms (Costa, 2007). Communication has been observed in Australian species Perga affinis and Perga dorsalis in the form of substrate borne vibrational cues made by a hardened cover on the tip of the abdomen being tapped on surfaces to signal group members to reunite (Costa, 2007). The North American red-headed pine sawfly, Neodiprion lecontei, has been found to use chemical cues to communicate with other members of the group (Costa, 2007). Below is a video showing the “tapping” communication in a Perga sp. in Australia.

The best example of chemical defence in the Symphyta larvae comes from the Australian Steel-blue sawflies (Perga sp.) found around South Eastern Australia - they are commonly known as ‘spit-fires’ as they eject an irritating fluid from their mouths as a defence against predation (Australian Museum, 2015). Below is a video showing the defensive behaviour of spit-fires.

References:

Barnard, P 2011, Royal Entomological Society Book of British Insects, Wiley-Blackwell, Hoboken NJ. pp. 226-267.

Costa, JT 2007, Social Sawflies, Department of Biology Western Carolina University, viewed 19 April 2015, <http://web.cortland.edu/fitzgerald/sawflies.html>

Gould, I & Bolton, B 1988, The hymenoptera, Oxford University Press, Oxford.

Wang, M, Rasnitsyn, AP & Ren, D 2014, ‘Two new fossil sawflies (Hymenoptera, Xyelidae, Xyelinae) from the Middle Jurassic of China’, Acta Geologica Sinica (English Edition), vol. 88, no. 4, pp. 1027-1033.

Steel-blue sawflies, Australian Museum, viewed 19 April 2015, <http://australianmuseum.net.au/steel-blue-sawflies>

Image 1: Melaleuca Sawfly (Lophyrotoma zonalis), viewed 19 April 2015, <http://www.ozanimals.com/image/albums/australia/Insect/Melaleuca-sawfly-1.jpg>

Image 2: Wang, M, Rasnitsyn, AP & Ren, D 2014, ‘Two new fossil sawflies (Hymenoptera, Xyelidae, Xyelinae) from the Middle Jurassic of China’, Acta Geologica Sinica (English Edition), vol. 88, no. 4, pp. 1027-1033.

Image 3: Only a mother could love them - Kristi Ellingsen, Australian Museum, viewed 19 April 2015, <http://australianmuseum.net.au/Uploads/Images/10229/OP105_Only%20a%20mother%20could%20l.jpg>

Video 1: Spitfires, youtube, viewed 19 April 2015 <https://www.youtube.com/watch?v=oNos7PDWjkg>

Video 2: Sawflies and spitfire grubs, youtube, viewed 19 April 2015 <https://www.youtube.com/watch?v=MB_oapTpIQk> 

Asian Honey Bee's and the threat to Australia

In 2007 the first colony of Asian Honey Bee or AHB (Apis cerana javana) was detected in Cairns, Queensland. There were attempts to eradicate this species, but in 2011 all attempts were declared unsuccessful and containment programs have since begun to control the spread of A. cerana (Australian Department of Environment, 2011).

If the world is currently facing a bee crisis of sorts; with Colony Collapse Disorder becoming a serious threat to Apis mellifera colonies throughout the globe, why are we so concerned about another species of bee becoming established here in Australia? Apart from the safety aspect (as many colonies are found close to human habitats), we will look at the other major issues with invasive bees.

Apis cerana javana swarm inside a letterbox in Cairns, Queensland.

We have had introduced European honey bee (A. mellifera) in Australia for 190 years and Bumble bees (Bombus terrestris) in Tasmania since 1992 – both species have created food and habitat competition to native species, with the B. terrestris competition creating displacement of 2 native bee species (Australian Department of Environment, 2011). It has also been found that Bumble bees pollinate invasive species so effectively they increase the seed viability of some of these invasive plants (Australian Department of Environment, 2011). AHB’s are an incredibly versatile species and are able to act as part of a colony (eusocial) and as a solitary individual as well as foraging from many minor sources of food (native and introduced species) rather than one crop – this contributes to the AHB’s highly successful ability to invade a region (Australian Department of Environment, 2011). So the AHB has the ability to be flexible in a range of environments, out-compete native species and contribute to the spread of invasive plants.

Apis mellifera & Bombus terrestris foraging on the same flowers

A. mellifera are established crop pollinators in Australia and are vital to the agricultural industry and food production. In 2008 it was estimated that the pollination services and the production of bee products in Australia was worth between $4 and $6 billion (Australian Department of Environment, 2011). The threat posed to A. mellifera by AHB’s (apart from competition) is that they are a natural host to the mites Varroa destructor and Varroa jacobsoni which are parasitic mites that feed on the larvae of the bee - these are non-natural parasites to A. mellifera (Australian Department of Agriculture, 2015).

Reproductive Varroa mite on a developing pupa (reddish oval) and two immature Varroa (opaque ovals). Credit: Abdullah Ibrahim (arrows added for emphasis)

It is believed that AHB’s have grooming behaviours that A. mellifera do not display and are therefore less likely to remove the parasites from brood (Carr, 2011). Varroa mites are responsible for the destruction and collapse of A. mellifera hives wherever it is present around the world – thankfully it is yet to be recorded in Australia but if it does arrive on our shores it will spread rapidly and is therefore considered the greatest threat to the honey bee industry (Queensland Department of Agriculture and Fisheries, 2015).

Here is a video showing ways that AHB colonies are destroyed here in Australia by Biosecurity Queensland – please do not try to remove colonies yourself, call a professional - these bees can sting, are venomous and will defend themselves if they are threatened.

References:

Invasive Bees, Australian Department of Environment, viewed 12 April 2015, <http://www.environment.gov.au/biodiversity/invasive-species/insects-and-other-invertebrates/invasive-bees>

The Asian Honey Bee in Australia, Australian Department of Agriculture, viewed 12 April 2015, <http://www.agriculture.gov.au/pests-diseases-weeds/bees/the-asian-honey-bee-in-australia>

Carr, AJ 2011, Asian honeybee: possible environmental impacts, Department  of  Sustainability, Environment, Water, Population and Communities,  Sustineo Pty Ltd, Canberra. 

Varroa mites, Queensland Department of Agriculture and Fisheries, viewed 12 April 2015, <https://www.daf.qld.gov.au/animal-industries/bees/diseases-and-pests/asian-honey-bees/general-information-on-varroa-mites>

Image 1 – Asian honey bee (Apis cerana) colony in mailbox, Queensland Department of Agriculture and Fisheries, viewed 12 April 2015, <https://www.daf.qld.gov.au/__data/assets/image/0004/53428/ahb-nest-letterbox.jpg>

Image 2 - Honey Bee Viruses: the Deadly Varroa Mite Associates, extension.org, viewed 12 April 2015, <https://www.extension.org/sites/default/files/pupavarroa.jpg>

Video 1 - Apis mellifera & Bombus terrestris - Sedum 'Matrona', youtube, viewed 12 April 2015 <https://www.youtube.com/watch?v=WiHP17AbQU4>

Video 2 - Asian honey bee destruction techniques for industry use by Biosecurity Queensland, youtube, viewed 12 April 2015 <https://www.youtube.com/watch?v=afrOmz7qXCk>

Mechanisms behind eusocial societies in hymenoptera - part 2

In the last blog, I discussed one of the driving mechanisms behind the evolution of socialism in hymenoptera – kin selection. In this entry I will look at another major driving force of socialism – maternal (or parental) manipulation.

Queens manipulate their offspring via genetic, physiological and behavioural avenues to ensure they remain within the colony to assist with raising their siblings (Gauld & Bolton, 1988). By doing this individuals forfeit their own breeding potential, form worker castes & enhance the queens reproduction potential (Gauld & Bolton, 1988). Much like the kin selection theory – the maternal manipulation theory requires prolonged mother-daughter relationships and overlapping generations (Gauld & Bolton, 1988).

Image 1 - Yellowjacket (Vespula spp.) queen, gyne, and males. 

In order for mothers to be able to manipulate their offspring without driving them away from the colony, the mother needs to move from basic parental care (such as that in pre-social wasps) into controlling the early development of her daughters so they will remain in the colony and assist in brood care (Brian, 1983). This manipulation may be driven by multiple factors including:

• Sex control that ensures a sterile worker caste and an exclusion of males until required (also derived from haplodiploidy)
• Moothers producing more offspring than required – a method which requires large numbers of substandard offspring to develop into a sterile worker caste through domestication – but this does not ensure that females will not leave the colony to create their own. This would require further manipulation through the development of a kin-help allele.
• The establishment of a gene which creates a sensitive phase during early development that can imprint a caste on the individual.

(Brian, 1983)

Image 2 - Red fire ant (Solenopsis invicta) castes and developmental stages.  Worker, male, and queen (top to bottom) adult, pupa, and larva (left to right).

Dawkins (1976) argues that even though the Queen has unchallenged control over her juvenile offspring, there must be some genetic symmetry otherwise the lack of any gain to the worker would allow cheat or non-cooperation genes to spread in offspring (Brian, 1983).

Two other theories have been hypothesised - one being polygyne families where many queens copulate but only the fittest queens are socially selected to produce brood and the least fit individuals are excluded after their brood is found to be inferior (Brian, 1983). 

Image 3 - Multiple queens in a colony of big-headed ants (Pheidole megacephala) in St. Lucia, South Africa. Image courtesy of Alex Wild.

The other is group selection where a population is split into sections (demes) that only come into genetic contact with each other briefly and rarely (Brian, 1983). Within the small population of the demes there is interbreeding which allows for random drift in allele frequency – this may lead to demes with unfavourable alleles dying off and demes with favourable alleles surviving (Brian, 1983). While these alleles may benefit a group they may be a disadvantage for the individual (e.g. sterility) however it has been found that the survival of a group is a direct function of the proportion of kin-help alleles (Brian, 1983). 

It seems that none of the theories surrounding the development of socialism in the hymenoptera are mutually exclusive and both kin selection and maternal manipulation have been a starting points for wasp and bee species to evolve into the complex societies we see today (Brian, 1983).

Video - Life Cycle of a Queen Honey Bee (Apis mellifera)

References:

Gould, I & Bolton, B 1988, The hymenoptera, Oxford University Press, Oxford.

Brian, MV 1983, Social Insects: ecology and behavioural biology, Chapman and Hall, London.

Dawkins, R 1976, The selfish gene, Oxford University Press, Oxford.

Image 1 – Yellowjacket (Vespula spp.) queen, gyne, and males on Goodisman Research Group, viewed 11 April 2015, <http://www.goodismanlab.biology.gatech.edu/Images_for_photos/Vmac%20queen,%20gyne,%20and%20males%20in%20nest.LG.jpg>

Image 2 - Red fire ant, Solenopsis invicta, castes and developmental stages on Goodisman Research Group, viewed 11 April 2015, <http://www.goodismanlab.biology.gatech.edu/Images_for_photos/Fire%20Ant%20Caste%20Development.AA3.Nov%202%202010.LG.jpg>

Image 3 – Multiple queens in a colony of Pheidole megacephala big-headed ants  St. Lucia, South Africa, viewed 11 April 2015 < http://www.alexanderwild.com/Ants/Taxonomic-List-of-Ant-Genera/Pheidole/i-8BHB924/2/XL/megacephala14-XL.jpg> 

Video - Life Cycle of a Queen Honey Bee, youtube, viewed 11 April 2015 <https://www.youtube.com/watch?v=aNoqN-IX5qs>