Arising pests? Or Predators?

Date: 25/02/2021

Time: 11:30AM–12:15PM

For the second pest surveillance, the same plot was revisited on a Sunny day with a temperature of 16°C, and a humidity of 54%. The surrounding was dry just like the soil, but the air had warmed up since the last time.

Observation

The prior insect pests observed were Aphids, Cabbage white butterfly larvae and harlequin bugs. Within a week’s span, there were major changes in the occurrence of the pests.

Aphids, had drastically increased in numbers, and most of the crops were completely devoured by aphids leaving dead dried crops standing. It had majorly affected bok choy, mustard greens and cabbages.

Figure 1. Ladybird beetle on its way towards Aphids

Figure 2. Bok choy after complete damage from aphids

On the other hand, due to the drastic increase in the number of uncountable aphids, the prevalence of Ladybird beetle and ladybird beetle larvae had also increased. There were around 25 ladybird beetles and more than 30 larvae vigorously feeding on the aphids.

Figure 3. Ladybird beetle devouring an aphid

Cabbage White Butterfly larvae was one of the most prominent pest on the field but within a week, they had decreased a lot. There were only around 6 larvae left, others all are assumed to have undergone metamorphosis towards the stage of an adult.

New Sights

• Hover Fly : Few hoverflies were seen nectaring over the flowers of Bok choy. Although the adults are only pollinators, the larvae of hover flies are predatory on aphids (Agriculture Victoria).

Figure 4. Hoverfly on Bok Choy flower

Reference List

Agriculture Victoria. (2021). Hoverflies. Retrieved from https://agriculture.vic.gov.au/biosecurity/pest-insects-and-mites/priority-pest-insects-and-mites/hover-flies