Friday, August 15, 2014

Biological Control Agents

Aulacidea pilosellae galls on Pilosella officinarum
(Credit: Jean-Yves Baugnée)
Two papers, two stories about insects that humans recruited for a specific mission - biological pest control. In an attempt to reduce the pestizide use we team up with predators and parasites (or parasitoids) of pest species. Some insects pests serve as prey for other arthropods (particularly spiders and mites), and several groups of vertebrates. Others are parasitized by various types of wasps and roundworms (nematodes) and are also attacked by a diverse group of pathogens including fungi, protozoa, rickettsiae, bacteria, and viruses. In addition a variety if arthropod species feed on plants and are used to control the spread of invasive flora. The biocontrol arsenal grows rapidly but every new introduction requires a series of tests before it is officially approved for use. The occurrence of such a candidate species in the region of proposed use can certainly expedite the approval process as there is no apparent risk of releasing another non-native and potential harmful species. 

The first story reports on such a case. The European gall wasp species Aulacidea pilosellae is a promising candidate that is supposed to help with a North American problem - invasive hawkweeds of the genus Pilosella. Two Canadian researchers apparently found this species in Canada:

Here we report the first North American detection of the gall wasp Aulacidea pilosellae Kieffer (Hymenoptera: Cynipidae), native to Central Europe and a promising candidate biological control agent for invasive hawkweeds (Pilosella Vaillant, Asteraceae) in North America. This occurrence was discovered through the intersection of (i) publically available DNA barcode data and (ii) DNA sequencing of a biocontrol agent before its release. COI DNA sequences of A. pilosellae collected in Central Europe were compared with publically available DNA sequence records.

As part of the host range assessment for the proposed biocontrol programme, DNA Barcode sequences of the European Aulacidea pilosellae were compared to all publicly available sequences on GenBank. The researchers found a COI sequence belonging to a specimen identified only to order, which differed by only one base pair. Surprisingly, this specimen was collected in eastern Ontario, Canada. Interestingly, it was this discovery that started communication between the two scientists, and once identity and origin of the specimen were verified, they decided to sequence a nuclear marker (28S-D2) to further substantiate their find. They found very little sequence variation between the specimen and its European counterparts(<0.2%). 

By detecting the presence of A. pilosellae in Canada, the process for approving this candidate biocontrol agent for release in North America may potentially be expedited. Regardless of the outcome of this particular case, there is clear potential significance of both (i) the DNA barcoding of candidate biocontrol agents and (ii) making publically available standardised DNA sequences even from un-identified specimens. 

Case closed.

United States National Collection
of Scale Insects Photographs Archive,
USDA Agricultural Research Service,
Invasive cactus species are certainly not a problem here in Canada but they have been causing problems in Australia since they escaped from early settlements. A number of species had became established as weeds, spreading considerable distances from the original point of introduction. 

Cochineals are scale insects of the genus Dactylopius which feed on a variety of cactus species. One species of scales (Dactylopius coccus) is the source for the crimson-colored natural dye carmine and it was this fact that brought the cacti to Australia as early settlers tried to start a cochineal dye industry in the late 1700s. Some Dactylopius species have been used successfully to control invasive cactus species. On of them is Dactylopius tomentosus which has a restricted host range within the Cactaceae, being associated only with species of the genus Cylindropuntia and according to story number two of today's post it consists of more specialized groups:

Recent studies have demonstrated that this scale is composed of host-affiliated biotypes with differential host specificity and fitness on particular host species. We investigated genetic variation and phylogenetic relationships among D. tomentosus biotypes and provenances to examine the possibility that genetic diversity may be related to their host-use pattern, and whether their phylogenetic relationships would give insights into taxonomic relatedness of their host plants.

The researchers used DNA Barcoding to investigate the genetic variation and phylogenetic relationships between Dactylopius tomentosus specimens from different localities and host plants. Their results were meant to improve the selection for biological control agents for invasive cacti.

Sequences of individuals from the same host plant within a region were identical and characterized by a unique haplotype. Individuals belonging to the same biotype but from different regions had similar haplotypes. However, haplotypes were not shared between different biotypes. Phylogenetic analysis grouped the monophyletic D. tomentosus into 3 well-resolved clades of biotypes. The phylogenetic relationships and clustering of biotypes corresponded with known taxonomic relatedness of their hosts.

In fact some of the observed intraspecific genetic divergences suggest that currently described Dactylopius species may be species complexes composed of cryptic or sibling species. Biological pest control is by no means a simple business.


Alex Smith (Aulacidea pilosellae story)
Scott Miller (Dactylopius tomentosus story)

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