Gall wasp project update - 2017 06: residual chemical trials

July 2017

Dr Jianhua Mo, Research Entomologist, Dept of Primary Industries

During the past season, the project team conducted a series of field and laboratory experiments exploring new chemical options to control citrus gall wasps (CGW). These included laboratory/shadehouse screening of contact and systemic insecticides; three field trials on pre-emergence chemicals; two deterrent field trials with a kaolin-based product, Surround™; and two systemic chemical field trials.

Five unregistered insecticides – an organophosphate insecticide (OP), a biologically derived insecticide (BD), a synthetic pyrethroid (SP1), a natural pyrethrum (NP), and a systemic insecticide (SYS1) – were investigated at the label rates for their contact activity against CGW adults in the laboratory at Yanco. The activities were compared with the registered insecticide methidathion and a unsprayed control. Two experiments tested for direct contact activity (insecticides directly applied to the body of the wasps) and one for indirect contact activity or residual activity (wasp picking up insecticides by contacting treated foliage).

Direct contact activity

All tested insecticides showed good direct contact activity against the adult wasps, with the organophosphate insecticide outperforming the others, including methidathion (Figure 1). The biologically-derived insecticide performed better than the synthetic pyrethroid and the systemic insecticide in one experiment.

Graph - contact author for accessible version

Figure 1. First-day mortality of adult citrus gall wasps after a small droplet of the test insecticide was placed on their bodies. Bars in the same group not sharing a common letter indicate significantly different mortalities. For an accessible version of this data contact Jianhua Mo.

Residual activity

With indirect contact activity, leaves treated with the organophosphate insecticide, biologically derived insecticide, synthetic pyrethroid, or systemic insecticide remained toxic to adult CGW wasps for up to seven days, killing >80% of the test wasps (Figure 2). The residual activity persisted for up to 14 days for the biologically derived insecticide, synthetic pyrethroid and systemic insecticide, which was longer than that for methidathion (seven days). Based on the screening results, all insecticides, except the natural pyrethrum, are worth further investigation in the field.

Graph - contact author for an accessible version

Figure 2. First-day mortality of adult citrus gall wasps after being confined with citrus leaves treated with a test insecticide 0, 3, 7, and 14 days ago. Bars in the same group not sharing a common letter indicate significantly different mortalities. For an accessible version of this data contact Jianhua Mo.

Pre-emergence activity

In an investigation of insecticides with pre-emergence activity (suppressing the emergence of CGW adult wasps), five insecticides: three systemic insecticide (SYS1, SYS2, and SYS3), one synthetic pyrethroid (SP2), and the registered methidathion, were applied at label rates to individual galls by brushing the chemicals directly on the galls.
Three trials were conducted in three separate citrus orchards in the Riverina. The chemicals were applied either one month, two weeks or one week before wasp emergence. Data analysis failed to detect any significant suppression of CGW emergence by any of the chemicals in any of the three trials (Figure 3). It is too early to dismiss the pre-emergence activity of the test chemicals as the results could have been due to poor uptake of the chemicals through the bark. New trials using foliar applications are needed to confirm or reject the pre-emergence activity of the chemicals.

Graph - contact the author for an accessible version of the data

Figure 3. Proportions of successful emergence of adult CGW wasps from galls treated with different chemicals. Wire bars show standard errors. For an accessible version of this data contact Jianhua Mo.

In late autumn, data on shadehouse screening of systemic insecticides, deterrent field trials of Surround™ and field systemic insecticide trials will be collected. These results will be reported later in a separate article.

For further information contact Jianhua Mo.