The ability of synthetic sex pheromone traps to forecast Plutella xylostella infestations depends on survival of immature stages

Abstract

The potential for using synthetic sex pheromone traps as a simple and practical method of monitoring population densities of insect pests has been investigated in many crop systems. Yet, factors enabling the forecast of infestations based on pheromone trap catches are not fully understood. This study tested the prediction that high survival of immature stages of the target pest is a pre‐requisite for trap catches to correlate well with future infestations on the crop. The influence of parasitoids, as an important natural mortality factor of diamondback moth, Plutella xylostella (L.) (Lepidoptera: Plutellidae), larvae and pupae in South Africa, on the ability of pheromone traps to forecast infestations was investigated continuously at weekly intervals over 6 years on unsprayed cabbage. During late October–May, when parasitism levels were high (≥50%), infestations and trap catches were significantly lower than during low parasitism (<50%) observed during June–early October. Because infestations were negatively related to parasitism level, trap catches correlated with infestations better when observations were made in the same week during periods of high parasitism. Conversely, when survival of P. xylostella immature stages was high due to low parasitism levels, trap catches correlated with future infestations well for up to 2 weeks. Thus, trap catches can be used to forecast infestations during September–October, a period that coincides with high P. xylostella infestations as a consequence of low natural control by parasitoids. This is the first study to show that the ability of pheromone trap catches to forecast infestations depends on survival of the immature stages of the target pest.

Disentangling factors limiting diamondback moth, Plutella xylostella (L.), spatio‐temporal population abundance: A tool for pest forecasting

“…Our results showed a significant positive correlation between number of moths with month, T max and T mean . This signifies that there is a general increase in the number of moths in the later months of the year (M > 6.25) than in the early ones (M < 6.25), still keeping with results by Kfir (1996) and Nofemela (2010). Similarly, an increase in T max and T mean resulted in an increase in number of moths as long as species optima (Karuppaiah & Sujayanad, 2012) and limits to key activity traits (Nyamukondiwa et al, 2013) were not exceeded.…”

“…Global positioning system (GPS) points were recorded for each trapping site using a Garmin® (GPSMAP 62 model, Olathe, KS, USA). (Kfir, 1996;Nofemela, 2010). From July to June in each of the 2015/2016 and 2016/2017 seasons, three yellow delta traps (spaced ̴ 50 m radius from each other) were mounted in each brassica plot on each farm (Supporting information Table S5; Figure 1) and a Thermocron i-Button (Cold Chain Thermodynamics®, model DS1923; Maxim, Sunnyvale, CA, USA) was placed on the "ceiling" inside one of the yellow delta traps to record shaded microclimate data (temperature and RH) at 1-hr intervals.…”

Population dynamics of the diamondback moth, Plutella xylostella (L.), in northern China: the effects of migration, cropping patterns and climate

“…The potential for using synthetic sex pheromone traps as a simple and practical method of monitoring population densities of insect pests has been investigated in many crop systems . We found continuous capture of P. xylostella during the cropping season from 2009 to 2015 for Changping and Haidian, and from 2009 to 2014 for Xuanhua and Zhangbei.…”

“…Traps baited with synthetic sex pheromone enable early detection of infestation 24 and can be used to estimate the level of infestations 25 and to investigate population dynamics of P. xylostella. 2 Here we used relatively long-term pheromone trap data (6-7 years) on the dynamics of P. xylostella across four locations (Haidian, Changping, Xuanhua and Zhangbei) in northern China.…”

Population Fluctuation and Vertical Distribution of the Soybean Looper (&lt;i&gt;Chrysodeixis includes&lt;/i&gt;) in Soybean Culture

“…A number of factors may influence the development of a predictive strategy with pheromones, including geographic variation [26], the impact of natural enemies on the pest population [27], the climatic conditions and the quality of the pest host plant [28].…”