The study provides baseline data on major insect pests of maize crops of Punjab, Pakistan. Maize, grown year-round is susceptible to various insect pests from seedling to harvest (Khan et al. 2022). The diversity, seasonal abundance, and population dynamics of these pests vary monthly. Over a two year survey in two major maize growing districts, 97671 arthropod pests from 49 species were recorded. The family Noctuidae was the most dominant at all six sampling sites, constituting nearly 50% of the total pest catch. Within this family, S. frugiperda was the most prevalent pest (18.51%); followed by Chilo partellus (14.94%), Helicoverpa armigera (13.84%) and H. zea (Boddie) (9.72%). The current findings align with Urge et al. (2020), who reported similar dominant pests in Ethiopian maize fields. Maize thrips (Frankliniella williamsi), maize aphids Rhopalosiphum maidis, Atherigona soccata, maize leafhopper (Cicadulina mbila) and Chaetocnema pulicaria constituted the sucking pest complex; targeting maize vegetative stages by extracting the plant sap (Paul et al. 2020). Furthermore, FAW; corn earworm (H. armigera & H. zea) and corn root worms (Agrotis ipsilon collectively form the chewing pest complex. They target the maize at different phenological stages by chewing different parts or by transmitting different types of bacteria and viruses (Soujanya et al. 2024). The sucking pests like leaf hopper, C. mbila usually attack the early vegetative and tasseling stages of maize. Maize aphids are widely prevalent pests; sucking the juice of the soft vegetative parts throws their mouthparts and serves as vector for the virus transmission (Oberemok et al. 2023).
Notably, FAW is a major invasive pest species of maize globally, infesting all stages of maize crops (Dassou et al. 2021). In our study, it was recorded as the dominant pest, comprising 18.51% of the total pest catch. FAW, a polyphagous insect also attacks other economic cash crops like rice, wheat, cotton, and sorghum (Mlambo et al. 2023). It causes a severe damage to the vegetative and reproductive parts of maize plants. Initially, young FAW larvae feed near the ground level. As they mature, the larvae start creating holes in leaves or stems from the outside inward. Mature leaves may have three to four rows of tiny holes (Day et al. 2017). Larval densities ranging from 0.2–0.8% per plant at the late whorl stage can result in 5–20% yield losses (Makgoba et al. 2021). FAW larvae hide within the maize funnel during the day and feed at night (Day et al. 2017). The presence of FAW on maize crops in Pakistan has been reported by other researchers. Gilal et al. (2020) reported 100% damage to fodder maize in Sindh district. Similarly, Ibrahim et al. (2022) found FAW in maize fields in Kasur and Lahore districts, with peak infection rates reaching 19.39%. Notably, damage was more severe at the edges of the maize fields compared to the central regions. This could be due to the probable migration of FAW from neighboring crops such as wheat and rice.
In addition to FAW, the study reported numerous other notable insect pests of maize crops in Pakistan. Maize steam borer, Chilo partellus from the family Crambidae was ranked as the second most abundant pest; constituting 14.94% of the total pest catches. This pest is globally widespread in maize; causing yield losses up to 42.29% (Guo et al. 2023). The larvae are more destructive, tunneling in the stem or stalk after hatching from eggs and hindering ear formation. They can move between plants through the holes made in the lower stem nodes (Srivastava et al. 2016). Nabeel et al. (2018) also identified this species as the main maize pest in Punjab, Pakistan. The Noctuid moths of Helicoverpa armigera (Hübner) (13.84%) and H. zea (Boddie) (9.72%) also caused significant losses in maize crops. These results are agreeable with those reported previously by Wang et al. (2023) in China. Moreover, Keszthelyi et al. (2016) reported that H. armigera can reduce average maize ear weight by 13.99%. It is also considered as key pest in agriculture and horticulture in Pakistan. On the other hand, H. zea is a polyphagous insect pest feeds on various crops especially maize. The larvae can damage both cultivated and wild host plants, particularly when feeding the maize ear. Their larvae initially feed on the silk and then move down to the ear tip. Previous studies by Sarwar (2023) confirmed the presence of H. zea in maize fields of Pakistan.
This study documented the presence of other pest species besides the dominant ones discussed earlier. These included maize aphids, grasshoppers, shoot flies, and white grubs. In this study, 96% of the species were successfully captured in both districts during the study period (2018 − 209). The remaining 4% of targeted crop pests might represent rare species, or their activity patterns or timing might have differed from the sampling schedule, leading to their undetected presence. This is evident in from species accumulation curves, which did not reach an asymptote at both districts. Similar findings were reported by Schmidt and Balakrishnan (2015), suggesting that various insect species may exhibit varying activity times to avoid competition. It is also possible that the methods for collecting insect pest samples weren't sufficient enough to guarantee a 100% complete pest inventory in both research regions. Furthermore, some pest species might only emerge sporadically during cropping seasons, potentially escaping capture during the sample phase. This is consistent with observations by other entomologists studying on the agricultural crops biodiversity. For example, Borges and Brown (1999) reported 90% completeness in their species inventory of arthropods in Azorean pasture, while Nadeem et al. (2023) recorded 94% of pest species from the cotton crops in Pakistan. This study revealed a distinct seasonal pattern in pest abundance during the cropping years (2018–2019). The number of insect pests began to increase in mid-March, reaching recorded peak in April. These findings align with the previous research conducted by Khan et al. (2022) in maize fields in Khyber Pakhtunkhwa, Pakistan. This data not only confirm the presence of predictable seasonal trends in pest populations, but also highlight the resilience of such patterns across various agricultural contexts in the Pakistan. The observed seasonal dynamics and minor changes in diversity indices are most likely caused by a combination of meteorological variables, crop phenology, and agricultural methods.
Given how temperature, humidity, and precipitation affect insect communities, it is possible that these climatic factors contributed to the very uniform diversity measurements observed (Vasconcellos et al. 2019). Furthermore, in addition to climatic conditions, other ecological factors, such as soil composition, vegetation structure, and land management methods, may have influenced local insect diversity patterns (Duan et al. 2021). The difference between the actual and estimated species richness using Chao-1 and Chao-2 estimator suggests that the sampling methods used to capture insect pests were not enough. It suggests that more intensive sampling efforts needed with additional sampling techniques for better capture of insect pests at both districts. Furthermore, extending the sampling time could also be an option for better pest capture. This approach may assist to capture a wider range of insect pests with diverse activity patterns throughout the day (Montgomery et al. 2021). The cluster analysis dendrogram revealed a clear grouping of sampling sites in both districts. This suggests that the pest communities share a similar geographic and environmental range. This observation is further supported by the minimal differences observed in maize field data collected from different sites within each district.
Climatic factors significantly impact the diversity of maize pests, influencing their population dynamics, distribution, and interaction with the natural predators (spiders, coccinellids, green lacewing) (Thomson et al. 2010). In the present research, FAW showed positive correlation (r = 0.750; p = 0.024) with the temperature consistent with the findings of Soumia et al. (2021). This might be due to enhanced reproductive rate and development of FAW in warmer conditions. Furthermore, the research revealed that maize stem borer (Chilo partellus) populations exhibited a positive correlation with temperature (r = 0.429; p = 0.274) while showing negative correlation with the rainfall (r = -0.106; p = 0.788) and humidity (r = -0.297; p = 0.481) levels. These finding suggest that higher temperatures favor proliferation of stem borer, whereas increase humidity and rainfall potentially due to the disruption of their habitat and life cycle. The results are supported by global research that has shown comparable trends and correlations between temperature, rainfall, humidity, and the abundance of maize stem borer populations (Régnier et al. 2023). In contrast to the above trends, maize aphids showed a negative association with temperature and a positive correlation with humidity levels. It is worth noting that the maize aphids observed in the current study were primarily found during the early vegetative phases (March and April) of maize crops. This could be because maize crops' tender stems and leaves produce more sap than mature crop stages (Șimon et al. 2023). In general, sucking pests dominated in April and May, while chewing pests were more prevalent from May to June (Murtaza et al. 2019).