Lipaphis erysimi (L.) Kaltenbach (Hemiptera: Aphididae) is one of the most important pests of brassica crops, mainly causing losses due to sap sucking, toxin injection and viral transmission. Knowledge about the main natural factors that regulate populations of this pest, as well as its critical mortality stage, is crucial for the development of integrated pest management of L. erysimi. Here, we determined the critical stage and key mortality factors for L. erysimi in cabbage using an ecological life table. Causes of mortality at each stage of L. erysimi development were monitored daily in the field for seven seasons. From the experimental data, we determined the key factor and critical stage of mortality through correlation and regression analyses. The nymphal stage, especially first instar nymphs, was critical for L. erysimi mortality. The key mortality factors were, in descending order of importance, physiological disturbances and predation by Syrphidae, Coccinellidae and Solenopsis ants. Therefore, control measures should target early stages of L. erysimi and the use of cabbage cultivars that have negative effects against L. erysimi may be a promising strategy for its management. Our results may be useful for plant geneticists who could develop new cabbage cultivars based on these findings. In addition, conservation measures of the main predators of L. erysimi may contribute to the natural control of this pest.

In the present study, we aimed to assess the suitability of predatory parameters, namely voracity, consumption index, conversion efficiency and growth rate, as measures of prey suitability. For this purpose, fourth-instar larvae and 10-day-old adult females of four co-occurring ladybirds, namely Coccinella septempunctata (L.) (C7), C. transversalis F., Cheilomenes sexmaculata (F.) and Propylea dissecta (Mulsant), fed on two essential species of aphid prey, Aphis craccivora Koch and Lipaphis erysimi (Kaltenbach), were observed. The results revealed that, with the exception of C7, the other three ladybirds performed better on A. craccivora. Previous studies based on reproductive and developmental attributes have also shown that A. craccivora is a more suitable prey for these three ladybirds, indicating a strong correlation and affirming the viability of using these measures as a mark of prey suitability. In a similar manner, fourth instars and adult females of C7 performed better on L. erysimi over A. craccivora. This detectable difference in consumption and utilization of aphid prey species by the four ladybirds indicates that these predatory parameters can be used as tools for assessing prey suitability in ladybirds.

Functional response of all instars, adult males and females of the ladybird Coccinella septempunctata L. was studied against two species of aphids, namely Lipaphis erysimi (Kalt.) and Brevicoryne brassicae L., infesting mustard and cabbage crops, respectively. The predatory stages of C. septempunctata exhibited a type II response on both the prey species. The attack rate was highest (0.0192) with the lowest handling time (7.9 min) when the adult female consumed L. erysimi. There was a significant difference in the predicted values of consumption of L. erysimi by fourth instars, adult males and females compared with those of B. brassicae, indicating that the former prey is preferred over the latter one. The adult females prey upon significantly more numbers of aphids than the adult males.

The functional response of fourth instars, adult males and females of the sevenspotted lady beetle, Coccinella septempunctata Linnaeus (Coleoptera: Coccinellidae), was studied at different densities of aphid, Lipaphis erysimi (Kaltenbach) (Homoptera: Aphididae). The maximum prey consumption was recorded for fourth instars at the highest prey density (800) and the minimum for the male lady beetle at the lowest prey density (25). The prey consumption by the predatory stages of the lady beetle was directly and the percent prey consumption inversely proportional to prey density. Prey handling time decreased with increasing prey density. Regression analysis showed a linear relationship between the log number of prey exposed for predation and prey consumed. The predatory efficiency of the predator stages was directly proportional to prey density, indicating a Holling Type II functional response.

The economic injury levels (EIL) of the mustard aphid, Lipaphis erysimi on mustard, Brassica juncea were evaluated in field trials in Tarai, India, during the winters of 1986/87 and 1987/88. The EIL values ranged between 37 and 4, and 48 and 6 aphids per 10 cm terminal shoot per plant during the 1986/87 and 1987/88 trials respectively. A one-day increase in crop exposure to the aphids led to a significant reduction in seed yield per plant, 1000-seed weight, number of siliquae per plant and number of seeds per siliqua. The highest benefit-to-cost ratio was obtained at 3 weeks of exposure, when initiation of insecticide application was most economical.

Studies on losses in yield of rapeseed, Brassica campestris cv. Brown Sarson, caused by the mustard aphid, Lipaphis erysimi (Kalt.) were conducted under natural and artificial conditions. Based on the experiments on the influence of aphid exposure to the crop on aphid number and seed yield and the effect of varied aphid population at flowering/pod initiation stage and artificial release of aphids at 10-day intervals starting from 40 days of sowing on the plant height, number of siliquae per plant, number of primary branches, seed yield per plant and 1000-grain weight, a positive correlation between length of aphid exposure to the crop and aphid population was found. A negative relationship between aphid population, length of aphid exposure and seed yield was observed. An inverse and significant relationship existed between parameters contributing to yield loss and losses in seed yield. However, this relationship was not significant in siliquae per plant and 1000-grain weight. A similar relationship was observed in artificial infestation.

A life table was constructed for the mustard aphid, L. erysimi during January, February and March corresponding to 14 ± 2°C, 16 ± 2°C, 20 ± 2°C and 74 ± 5%, 74 ± 6% and 54 ± 5% R. H. under laboratory conditions. The study revealed that the values of intrinsic rate of natural increase (rm) and finite rate of increase (λ;) were 0.1035, 0.096, 0.023 and 1.109, 1.101, 1.023 females/female/day. The doubling time (DT) was higher in the case of alate morph during March (13.088 days) than apterous morph during January (6.697 days) and February (7.220 days). On reaching the population at a stable age distribution, the nymphal population estimated was 84.36, 93.87 and 92.67 in January, February and March respectively. The life expectancy (ex) of newly born nymphs of L. erysimi declines monotonically with advancing of age in these months.

The present study revealed that the ratio of antennal to body length in Lipaphis erysimi (Kalt.) increased from 0.55: 1.00 in the first instar to 0.75: 1.00 in the adult alatae as compared to apterae, where the ratio stayed almost the same. The antenna showed specific growth regions i.e. first and fourth annuli, where the increase in size was more compared to other parts. Five morphologically distinct types of sensilla were recorded i.e. sensilla companiform. sensilla trichodea with enlarged spatulate tips, sensilla trichodea with tapering uniporous tips, plate organs and coeloconic pegs. The distribution pattern of these sensilla showed that the number of sensilla trichodea increased during the development, the increase was more in alatae compared to apterae. The secondary sensoria were restricted to adult alatae only, but could be seen under the cuticle in fourth instar alatae. In addition, the variation in the surface sculpturing in the form of scale-like projections were also observed on the antenna.

The leaf surface treatment given to nymphal instars of Lipaphis erysimi with methoprene (1–10,000 ppm) prolonged the developmental period only in the second instar. The percentage emergence decreased significantly in the treatments of first and second instar and the alate production increased in the treatment of the latter instar only. In addition, dose-dependent morphological abnormalities were also observed. The longevity and fecundity were affected adversely when adults were given both topical and leaf surface treatments. However, these effects were not transmitted to the F1 generation.