Study on the life table parameters of the cabbage aphid, Brevicoryne brassicae (L.) (Hemiptera: Aphididae) influenced by sublethal concentrations of the matrine

Brevicoryne brassicae is one of the most serious cabbage pests in the world. This pest feeds on the leaves, mostly on the host plant's middle leaves. Despite having many natural enemies, aphids are not entirely controlled by natural enemies due to their rapid reproduction. Applying chemical insecticides is one of the essential methods used to control aphids; using one pesticide to control several pests can reduce the costs and frequency of spraying. In this study, the lethal and sub-lethal effects (LC25) of matrine insecticide with a contact and stomach function on the cabbage aphid, were evaluated under laboratory conditions.

The dipping method was used in bioassay and life table studies against adults of aphid insects. The LC50 value of matrine insecticide for adults of cabbage aphid was 83.33 μl/ml after 24 hours, and LC25 concentration (30.11 ml/ml) was used to estimate the sub-lethal effects of matrine on the biological parameters of the cabbage aphid. Experiments were performed on the acephala variety of cabbage. One common method of investigating insecticides' non-lethal effects is demographic toxicology, which uses life table and growth population parameters to evaluate toxicity.

According to the results, the female lifespan/longevity and fertility affected by sub-lethal concentration were significantly reduced compared to the control (distilled water and citowett). The mean oviposition period of adult aphids decreased from 8.92 days in control to 3.79 days in LC25 concentration of the insecticide. The present study's data also showed that the sublethal concentration also affected the offspring of treated cabbage aphids. Accordingly, the sublethal concentration of matrine reduced the net reproductive rate (R0) from 23.96 nymphs per female in each generation in the control treatment to 3.26 nymphs in LC25. The intrinsic rate of increase (r) in sublethal concentration was recorded as 0.36 (day-1) and in control as 0.1 (day-1). Other parameters, such as finite rate of increase (l) and gross reproductive rate (GRR), were also significantly lower than the control. The mean generation time (T) of treatment affected by LC25 concentration of matrine increased compared to the control treatment.

Results of the current research in laboratory conditions showed that this insecticide has significant lethal and sublethal effects on the cabbage aphid. Therefore, matrine, as an herbal insecticide, can be considered in the management programs of cabbage aphids.