The strawberry is not a true fruit since the botanical fruits are the small, hardened achenes that everybody refers to as “seeds” distributed on the outside of the ripened receptacle that contains all of the sugars and vitamins that we look forward to eating. Be that as it may, this achene arises from a single ovule in the flower when it is fertilized by pollen most often provided by the same flower, and once pollinated, this ovule starts to not only develop itself, but also contribute to the growth of the fleshy receptable around it. All of the ovules on a strawberry, very roughly maybe 200 of them, developing and growing the receptacle closely around them are what result in the fleshy strawberry fruit.
Where the interest in this process to the grower should come about, is when the ovules on individual flowers fail to be fertilized, for example by temperature and moisture extremes, the plant being undernourished, and the feeding activities of insects such as Lygus bug. In these cases, the failure of the ovule to be pollinated means also that the achene does not form and would not contribute to the growth of the fruity and fleshy receptacle around it. Having many failures to pollinate on the receptacle results in what many refer to as the unsightly cat-facing and twisting of the fruit, which renders it unmarketable since consumers really want to buy something that not only tastes good but looks good too.
It is also becoming pretty evident, based on research done in the field that loss of ovules in a flower and subsequent reduction of achenes doesn't necessarily twist the fruit, but can result in smaller fruit. This makes sense because smaller fruit always have lower numbers of achenes than larger fruit. A paper published in 1950 by J. P. Nitsch at Cal Tech shows a clear linear relationship between fruit weight and the number of fertilized achenes (Figs. 1 and 2).
Mark has seen this in his own work where a reduction in the Lygus bug population not only resulted in less cat-facing but also in larger fruit. In two separate trials in 2022 and 2024 average fruit size was found to be significantly greater in plots treated with the highly effective plinazolin insecticide compared to the untreated control and some of the other treatments. In the 2022 trial, fruit sizes were nearly 40% larger (22 g compared to 16 g per fruit) in plinazolin treated plots compared to those not treated at all or treated with a pyrethroid standard. That this gain in fruit size squared with much lower Lygus bug populations in these plinazolin treated plots in both cases is notable.
Referenced paper: Nitsch, J. P. 1950. Growth and morphogenesis of the strawberry as related to auxin. Amer. J. Botany 37:211-215.