## 4 Discussion
### Variety and Nitrogen Effects on Planthopper and Leafhopper Abundance  
Several previous studies of IR62 have indicated that the variety has strong antixenosis and antibiosis defenses [49; 54; 57]. In greenhouse and field cages, the build-up of BPH populations on IR62 is curtailed over successive generations and populations may eventually collapse, even in the absence of natural enemies [58]. Our experiments were conducted on relatively young plants because maximum egg laying by BPH and WBPH occurs in young plants [59] and egg parasitoids are most abundant at early crop stages [38; 60]. We found  
\begin{table}
\begin{tabular}{c c c c c c} \hline \hline
**Herbivores 1** & **Parasitiods** & **Variety** & **Nitrogen** & **Season** & **Interaction Effects 2** & **Egg Density** \\  & **Effect 2** & **Effect 2** & **Effect 1,2** & **Effect 1,2** & **(Covariate) 2** \\ \hline \hline Abundance in sweep-nets & & & & & \\   BPH & ns & ns & WS *** & ns & \\   WBPH & ns & - & - & Low nitrogen \(\times\) WS ** \\   GLH & & IR64 *** & Low ** & WS *** & ns \\  & _Oligosita_ spp. & ns & ns & WS *** & ns \\  & _Anagrus_ spp. & ns & ns & WS *** & ns \\  & _Gonatecrus_ spp. & ns & ns & WS *** & ns \\ Parasitism of eggs & & & & & \\   in sentinel plants & & & & &  
no significant effect of variety on egg laying by either planthopper species, or by GLH (Table S1); however, recent studies have shown that egg laying by BPH under no-choice conditions is heavily affected by the host of the female parent (i.e., TN1 in this study), with reductions in egg laying apparent as a lack of successive oviposition cycles [61]. The success of IR62 therefore relies on effective suppression, or losses in the reproductive potential of early generations of nymphs produced by immigrating females, which occurs during early crop stages. Variety effects may be more apparent at later crop stages, but these effects are initiated in the early crop. Therefore, a lack of apparent variety effects on planthoppers in our field plots (Figure 1A,B) may be due to the early crop stage at which sampling was conducted, but could also be due the low captures (BPH), and only late-stage resistance in IR62 to WBPH [31]. In contrast to planthoppers, GLH was, as expected, less abundant in plots of IR62 (Figure 1A,B).  
A number of studies have shown that the fitness (survival \(\times\) reproduction) of BPH, WBPH and GLH increases under high nitrogen [54; 59; 62; 63]. Based on these reports, we expected that planthopper and leafhopper densities would be higher in high-nitrogen plots; however, sweep-net sampling indicated that GLH were consistently more abundant in the low-nitrogen plots (Figure 1A,B); WBPH were also more abundant in low-nitrogen plots during the wet season (Figure 1B). These results agree with results from previous sampling at the same plots in different years as reported by [PERSON] et al. (2019) [22]. The lower abundance of WBPH and GLH in low-nitrogen plots, despite clear benefits of high nitrogen for these species, suggests that mortality is higher in high-nitrogen plots. Outbreaks of BPH have been associated with excessive fertilizer use [4; 64]; however, nitrogenous fertilizer had no apparent effect on BPH numbers in our study (Figure 1A,B). A lack of apparent effects in our study may be because the species occurred at low densities (generally below economic threshold densities), and, as with variety effects (explained above), the effects of nitrogen may be more apparent during later crop stages when second- or third-generation planthoppers occur [4; 5]. Nevertheless, our study did find significant variety and nitrogen effects on egg parasitism.